Secondary Erythromelalgia

Complex MONDO:0035149 Pathograph 15 Show in embeddings browser disease

Secondary (acquired) erythromelalgia is erythromelalgia arising in the context of an identifiable underlying disorder rather than from an inherited sodium-channel lesion. Its best-characterized and best-evidenced form is the erythromelalgia of the myeloproliferative neoplasms (MPN) — essential thrombocythemia and polycythemia vera — where the mechanism is not nociceptor channelopathy but platelet-mediated arteriolar inflammation and thrombotic occlusion of the acral microvasculature. Skin punch biopsies from affected areas show arteriolar inflammation, fibromuscular intimal proliferation, and platelet-rich thrombotic occlusions; platelet survival is shortened, platelet activation markers are elevated, and the entire syndrome is abolished by cyclooxygenase inhibition. Other acquired routes — autoimmune connective-tissue disease, small-fiber peripheral neuropathy, and drug exposure — are recognized but far less mechanistically resolved. This entry is the acquired sibling of `Primary_Erythermalgia` (SCN9A/Nav1.7 gain-of-function) and sits beneath the umbrella entry `erythromelalgia`; the two are distinguished mechanistically (platelet-microvascular versus neuronal-channelopathy) and therapeutically (the dramatic aspirin responsiveness of MPN-associated disease versus the characteristic aspirin refractoriness of the primary form). The underlying MPN pathophysiology itself is curated in `Polycythemia_Vera` and `Essential_Thrombocythemia` and is deliberately not re-derived here.

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1
Mappings
7
Pathophys.
6
Phenotypes
2
Gaps
15
Pathograph
6
Medical Actions
2
Differentials
1
Deep Research
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Mappings

ICD-10-CM
ICD10CM:I73.8 Other specified peripheral vascular diseases
skos:broadMatch MONDO:0035149
MONDO:0035149 carries ICD10CM:I73.8 as a cross-reference. The predicate is broadMatch, not exactMatch: I73.8 is a residual "other specified peripheral vascular diseases" bucket that does not distinguish primary from secondary erythromelalgia, so an ICD-10-CM-coded cohort cannot be used as a case definition for this entry.
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Discussions and Knowledge Gaps

2
How does an arteriole occluded by platelet-rich thrombi produce a skin surface that is visibly red and *hotter* than normal? Is microvascular arteriovenous shunting the reconciling mechanism, and if so does it operate in the MPN-associated form or only in the non-platelet acquired routes?
KNOWLEDGE GAP OPEN av_shunting_vs_occlusion_paradox
Attached to
pathophysiology#Episodic Acral Burning Pain, Erythema, and Warmth pathophysiology#Acral Arteriolar Microvascular Occlusion
This entry's occlusive model has an unresolved surface paradox. The demonstrated lesion is arteriolar obstruction by platelet-rich thrombi, which should reduce perfusion — yet the defining clinical sign is a red, warm, congested extremity, and the flare node above therefore deliberately binds no `vasodilation` process rather than assert a mechanism it cannot evidence. The classical reconciliation is microvascular arteriovenous shunting: blood bypasses the nutritive capillary bed through shunts, so the skin is simultaneously hyperemic and warm at the surface while the tissue itself is hypoxic. That model is asserted in the older review literature (PMID:15075045) but, critically, is asserted there as a *single common mechanism for all* erythromelalgia — a claim the later Nav1.7 channelopathy findings contradict, and which this KB already flags as PARTIAL on the umbrella `erythromelalgia` entry. The deep-research report for this entry describes the same shunting model with a low-transcutaneous-oxygen correlate, but its only source there is a textbook chapter with no PMID and no quotable passage, so it cannot be curated as an evidence-backed pathophysiology node. What would settle it: paired measurements in *aetiologically stratified* patients — laser Doppler skin blood flow and transcutaneous oxygen tension during a flare, in MPN-associated versus non-MPN secondary disease. Until then this entry models only what the histopathology and platelet kinetics directly demonstrate, and records the shunting hypothesis here rather than promoting it to a node.
Show evidence (2 references)
PMID:15075045 SUPPORT Other
"A wide variety of etiological conditions can cause erythromelalgia, all having a single common pathogenetic mechanism - microvascular arteriovenous shunting."
States the arteriovenous-shunting hypothesis. Support is PARTIAL and deliberately so: this 2004 review asserts shunting as the SINGLE common mechanism across all erythromelalgia, which the SCN9A/Nav1.7 findings curated in `Primary_Erythermalgia` contradict. It is cited as the source of an open hypothesis, not as support for a curated mechanism.
PMID:8883266 SUPPORT Human Clinical
"intravascular activation and aggregation of platelets with subsequent sludging or occlusion of the acral arterial microvasculature"
Establishes the occlusive half of the paradox — the demonstrated lesion in MPN-associated disease is microvascular occlusion, which is what makes the warm, hyperemic surface appearance require an explanation.
Does MONDO:0035149 "secondary erythromelalgia" include the platelet-mediated erythromelalgia of the myeloproliferative neoplasms, or only the aspirin-resistant non-MPN acquired forms that the historical Drenth-Michiels classification called "secondary erythermalgia"?
KNOWLEDGE GAP OPEN secondary_em_nomenclature_scope
Attached to
pathophysiology#Clonal Thrombocythemia in Myeloproliferative Neoplasm pathophysiology#Non-Platelet Acquired Routes (Neuropathic, Autoimmune, Drug-Induced)
Two incompatible nomenclatures are in circulation. The historical Drenth-Michiels scheme is three-way and defined by aspirin responsiveness: (a) aspirin-responsive erythromelalgia in thrombocythemia, (b) aspirin-resistant primary erythermalgia, (c) aspirin-resistant "secondary erythermalgia" associated with other medical conditions. Under that scheme, MPN-associated disease is NOT "secondary". Contemporary usage is instead a two-way primary/secondary split that places MPN-associated disease squarely within "secondary" — the Olmsted County population study classified patients as secondary precisely when they had a coexisting myeloproliferative disorder, and a 2025 systematic review lists myeloproliferative disorders first among the conditions secondary EM is linked to. This entry follows that contemporary usage and models the MPN platelet arm as the principal, best-evidenced secondary mechanism, while retaining the non-MPN routes as a separate, deliberately low-resolution node. THE GAP, stated precisely: which of the two senses MONDO:0035149 itself intends is NOT established here. Its only synonym is "Secondary erythermalgia" EXACT [Orphanet:529864] — i.e. Orphanet's label is the very term the historical narrow scheme used for the aspirin-RESISTANT non-MPN category. No Orphanet definition row was quotable at curation time (the Orphadata bulk XML was not available locally), so this entry's scope decision rests on contemporary clinical/epidemiological usage rather than on a cited ontology definition. Resolving it needs `just structured-rebuild-orphanet --id 529864` and a quoted `ORPHA:529864` definition row. Curators reading the older literature should meanwhile note that "secondary erythermalgia" there means something narrower than this entry's scope, and that the aspirin-responsiveness contrast is therefore a contrast between the MPN arm and everything else, not between "secondary" and "primary" as such.
Show evidence (2 references)
PMID:32491719 SUPPORT Other
"(a) Erythromelalgia in thrombocythemia: It is platelet mediated and aspirin responsive. This occurs in association with essential thrombocytosis and polycythemia vera."
Documents the historical three-way classification in which thrombocythemic erythromelalgia is its own aspirin-responsive category, separate from "secondary erythermalgia".
PMID:18713229 SUPPORT Human Clinical
"Patients were considered to have secondary erythromelalgia if they had a coexisting diagnosis of a myeloproliferative disorder such as polycythemia vera, chronic myelocytic leukemia, or thrombocythemia at the time of diagnosis of erythromelalgia"
Contemporary epidemiology classifies MPN-associated disease as secondary, the usage this entry follows and the one matching MONDO/Orphanet.
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Pathophysiology

7
Clonal Thrombocythemia in Myeloproliferative Neoplasm
The upstream trigger of MPN-associated erythromelalgia is the clonal thrombocythemia of essential thrombocythemia or polycythemia vera, which supplies a population of qualitatively abnormal, hyperactivatable platelets. The dependence is causal rather than merely associative: erythromelalgia remits during cytoreduction-induced haematological remission and recurs when the thrombocythemia relapses. Notably the threshold is low — symptoms occur at platelet counts only slightly above normal — so absolute platelet mass is not the determinant. The clonal driver biology itself (JAK2 V617F and the haematopoietic consequences) is curated in `Polycythemia_Vera` and `Essential_Thrombocythemia`.
platelet CL:0000233 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves platelet (CL:0000233). CL:0000233 is a cell type from the Cell Ontology. megakaryocyte CL:0000556 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves megakaryocyte (CL:0000556). CL:0000556 is a cell type from the Cell Ontology.
Downstream
Thromboxane-Dependent Platelet Activation and Aggregation The clonal platelet population undergoes intravascular cyclooxygenase-dependent activation and aggregation.
Show evidence (3 references)
PMID:3977194 SUPPORT Human Clinical
"The erythromelalgia was alleviated during busulfan-induced remissions of thrombocythemia and its recurrence coincided with relapsing thrombocythemia."
Remission-and-relapse concordance with the underlying thrombocythemia establishes the MPN as the causal upstream driver rather than a coincidental association.
PMID:9263352 SUPPORT Other
"Erythromelalgia is a characteristic thrombotic complication in patients with the myeloproliferative disorders, essential thrombocythemia and polycythemia vera."
Identifies the two myeloproliferative neoplasms that constitute the principal underlying disorders of this secondary form. Classified OTHER because this is a narrative minireview summarizing the authors' prior work rather than a report of primary data.
PMID:8951772 SUPPORT Human Clinical
"Erythromelalgia in thrombocythemia already occurred at slightly increased platelet counts above 400 x 10(9)/l."
Symptoms arise at only slightly elevated platelet counts, indicating that qualitative platelet hyperreactivity rather than absolute platelet mass drives the mechanism.
Thromboxane-Dependent Platelet Activation and Aggregation
Circulating MPN platelets undergo intravascular activation and aggregation in the acral microcirculation. The process is strictly cyclooxygenase-metabolite dependent: it is abolished by aspirin and indomethacin but not by sodium salicylate or by non-COX platelet inhibitors (dipyridamole, sulfinpyrazone, ticlopidine, dazoxiben). In vivo activation is measurable as elevated beta-thromboglobulin, platelet factor 4, thrombomodulin, and urinary thromboxane B2, together with a markedly shortened platelet survival time that aspirin normalizes. Critically, thrombin generation is NOT required — prothrombin fragment 1+2 and fibrin degradation products are unchanged, and the lesions develop despite heparin or coumarin anticoagulation.
platelet CL:0000233 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves platelet (CL:0000233). CL:0000233 is a cell type from the Cell Ontology.
platelet activation GO:0030168 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased platelet activation (GO:0030168). GO:0030168 is a biological process from the Gene Ontology. ↑ INCREASED platelet aggregation GO:0070527 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased platelet aggregation (GO:0070527). GO:0070527 is a biological process from the Gene Ontology. ↑ INCREASED prostanoid (thromboxane) biosynthesis GO:0046457 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased prostanoid (thromboxane) biosynthesis, annotated with prostanoid biosynthetic process (GO:0046457). GO:0046457 is a biological process from the Gene Ontology. ↑ INCREASED
platelet cyclooxygenase-1 activity GO:0004666 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves platelet cyclooxygenase-1 activity, annotated with prostaglandin-endoperoxide synthase activity (GO:0004666). GO:0004666 is a molecular function from the Gene Ontology.
Downstream
Arteriolar Inflammation and Fibromuscular Intimal Proliferation Activated platelets and their released mediators injure and remodel the arteriolar wall.
Acral Arteriolar Microvascular Occlusion Platelet aggregates sludge and occlude the acral arterial microvasculature.
Show evidence (6 references)
PMID:3977194 SUPPORT Human Clinical
"Complete relief of pain and restoration of microvascular circulation disturbances was obtained with the cyclo-oxygenase inhibitors aspirin and indomethacin, but not with sodium-salicylate or the platelet inhibitors dipyridamole, sulfinpyrazone, ticlopidine, and dazoxiben."
The pharmacological dissection — COX inhibitors work, other antiplatelet agents do not — establishes cyclooxygenase metabolites as mechanistically necessary.
PMID:12781799 SUPPORT Human Clinical
"Thus, cyclooxygenase metabolites are necessary for erythromelalgia to develop."
States the necessity of cyclooxygenase metabolites explicitly.
PMID:12781799 SUPPORT Human Clinical
"significant higher levels of platelet activation markers beta-thromboglobulin, thrombomoduline and increased urinary thromboxane B2 excretion in thrombocythemia patients suffering from erythromelalgia"
Quantifies in vivo platelet activation and thromboxane generation specifically in symptomatic patients.
+ 3 more references
Arteriolar Inflammation and Fibromuscular Intimal Proliferation
Skin punch biopsies taken from erythromelalgic areas show a distinctive arteriolar lesion — inflammation of the arteriolar wall with fibromuscular proliferation of the intima — accompanying the thrombotic occlusions. This inflammatory and proliferative wall response, together with the elevated thrombomodulin indicating endothelial injury, distinguishes the lesion from a bland intraluminal clot and is what makes "platelet-mediated arteriolar inflammation" rather than simple thrombosis the accurate description.
arteriolar endothelial cell CL:0000115 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves arteriolar endothelial cell, annotated with endothelial cell (CL:0000115). CL:0000115 is a cell type from the Cell Ontology. arteriolar smooth muscle cell CL:0000192 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves arteriolar smooth muscle cell, annotated with smooth muscle cell (CL:0000192). CL:0000192 is a cell type from the Cell Ontology.
inflammatory response GO:0006954 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased inflammatory response (GO:0006954). GO:0006954 is a biological process from the Gene Ontology. ↑ INCREASED smooth muscle cell proliferation GO:0048659 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased smooth muscle cell proliferation (GO:0048659). GO:0048659 is a biological process from the Gene Ontology. ↑ INCREASED
arteriole UBERON:0001980 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in arteriole (UBERON:0001980). UBERON:0001980 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Acral Arteriolar Microvascular Occlusion Intimal proliferation narrows the arteriolar lumen and compounds platelet-driven occlusion.
Show evidence (2 references)
PMID:3977194 SUPPORT Human Clinical
"Skin punch biopsy samples taken from the affected areas showed typical arteriolar inflammation, fibromuscular intima proliferation, and thrombotic occlusions."
Direct histopathological demonstration of the arteriolar inflammatory and intimal-proliferative lesion in affected skin.
PMID:12781799 SUPPORT Human Clinical
"the demonstration of arteriolar fibromuscular intimal proliferation and occlusions by platelet-rich thrombi in skin biopsies"
Independently restates the arteriolar intimal-proliferative and platelet-rich occlusive histopathology.
Acral Arteriolar Microvascular Occlusion
The convergent lesion is occlusion of acral arterioles by platelet-rich, von Willebrand factor-positive thrombi with only weak fibrin content. The resulting acral perfusion disturbance is the immediate substrate of the erythromelalgic flare and, if unrelieved, of progressive digital ischemia. The VWF-rich, fibrin-poor composition of these thrombi is the histological counterpart of the biochemical finding that thrombin generation is dispensable.
arteriole UBERON:0001980 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in arteriole (UBERON:0001980). UBERON:0001980 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Episodic Acral Burning Pain, Erythema, and Warmth Acral microvascular occlusion and the accompanying congestion produce the erythromelalgic attack.
Progression to Acrocyanosis and Digital Ischemic Necrosis Untreated, sustained occlusion progresses to fixed acral ischemia.
Show evidence (2 references)
PMID:8883266 SUPPORT Human Clinical
"Histopathologic and immunohistochemical analysis of biopsies derived from erythromelalgic skin areas of 2 ET patients showed that erythromelalgic thrombi stained positively for von Willebrand factor opposed to only a weak fibrin staining."
Immunohistochemistry establishes the VWF-rich, fibrin-poor composition of the occluding thrombi, distinguishing them from conventional fibrin-platelet thrombi.
PMID:3977194 SUPPORT Human Clinical
"platelet-mediated inflammatory and occlusive arteriolar changes play a part in the etiology of erythromelalgia"
Summarizes occlusive arteriolar change as the operative lesion in the aetiology of the syndrome.
Episodic Acral Burning Pain, Erythema, and Warmth
The clinical expression is the erythromelalgic attack: localized burning pain with redness and warm congestion of the distal extremities, documentable by thermography, most often in the forefoot sole and toes and less often in the fingertips or palm. Unlike the bilaterally symmetric flares of the primary form, secondary attacks are frequently asymmetric or unilateral, and erythromelalgic "hot spots" on the legs can be misread as superficial thrombophlebitis. No `biological_processes` are bound to this node: the obvious candidate (vasodilation) is not measured by any cited study and would sit awkwardly against this entry's occlusive model, in which the red, warm skin accompanies platelet-rich arteriolar obstruction rather than simple vasodilation.
Show evidence (3 references)
PMID:3977194 SUPPORT Human Clinical
"The localized painful burning, redness, and warm congestion in the extremities could be accurately documented with thermography."
Describes the flare phenotype and its objective thermographic correlate.
PMID:8951772 SUPPORT Human Clinical
"Erythromelalgia was localized in the forefoot sole and toes in 28, the fingertips in 9, the handpalm in 2."
Quantifies the acral, foot-predominant anatomical distribution of attacks in a 50-patient thrombocythemia series.
PMID:32491719 SUPPORT Other
"Although erythromelalgia is typically bilateral, it can present unilaterally, especially in secondary cases."
Supports asymmetric/unilateral presentation as a feature that clinically distinguishes secondary from the characteristically bilateral primary form.
Progression to Acrocyanosis and Digital Ischemic Necrosis
When the platelet-mediated occlusive process is not interrupted, the reversible erythromelalgic flare progresses to fixed acral ischemia: acrocyanosis and then frank ischemic necrosis or gangrene of toes or fingertips. This ischemic-progression arm is a mechanistically distinct outcome from the self-inflicted cold-immersion tissue injury that dominates complications in the primary form, and it is the reason MPN-associated erythromelalgia is treated as a thrombotic complication rather than purely a pain syndrome.
Show evidence (2 references)
PMID:3977194 SUPPORT Human Clinical
"Erythromelalgia often progressed to ischemic acrocyanosis or necrosis in toes or fingers."
Documents progression from the reversible flare to fixed acral ischemic tissue loss.
PMID:8951772 SUPPORT Human Clinical
"Untreated erythromelalgia progressed to acrocyanosis or peripheral ischemia with necrosis in a toe or fingertip in 14 cases."
Quantifies ischemic progression in 14 of 50 thrombocythemia patients when erythromelalgia was left untreated.
Non-Platelet Acquired Routes (Neuropathic, Autoimmune, Drug-Induced)
Beyond the myeloproliferative neoplasms, erythromelalgia is reported secondary to small-fiber peripheral neuropathy, autoimmune connective-tissue disease, and drug exposure. These routes are recognised clinically but are far less mechanistically resolved than the MPN arm: combined neural and vascular abnormalities are invoked rather than a single demonstrated lesion, and critically these forms do NOT share the aspirin responsiveness of the platelet-mediated arm, which is why the historical Drenth-Michiels classification separated aspirin-resistant "secondary erythermalgia" from aspirin-responsive thrombocythemic erythromelalgia. Curated here as a deliberately low-resolution node rather than a speculative mechanism chain.
Downstream
Episodic Acral Burning Pain, Erythema, and Warmth These acquired routes converge on the same clinical flare phenotype by mechanisms that remain incompletely defined.
Show evidence (6 references)
PMID:40428878 SUPPORT Human Clinical
"It is often linked to underlying conditions such as myeloproliferative disorders (e.g., essential thrombocythemia, polycythemia vera), autoimmune diseases, infections, tumors, or medication use"
Enumerates the acquired etiologies named in this node — autoimmune disease, infection, neoplasia and drug exposure alongside the myeloproliferative neoplasms.
PMID:18713229 SUPPORT Human Clinical
"if the erythromelalgia was thought to be attributable to another cause such as medications, human immunodeficiency virus, or mushroom poisoning"
A population-based study's own case definition independently names the drug, infection and toxin routes as recognized non-MPN causes of secondary erythromelalgia.
PMID:15075045 SUPPORT Other
"secondary, which is associated with myeloproliferative disorders-related thrombocythemia, polycythemia, collagen-vascular diseases, diabetes mellitus, peripheral neuropathy, autoimmune and infectious diseases, and use of certain medicaments"
Names the acquired associations modeled by this node — collagen-vascular disease, diabetes mellitus, peripheral neuropathy, autoimmune and infectious disease, and drug exposure — alongside the myeloproliferative route curated separately above.
+ 3 more references
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Secondary Erythromelalgia Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

6
Blood 1
Thrombocytosis HP:0001894 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Thrombocytosis (HP:0001894). HP:0001894 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:8951772 SUPPORT Human Clinical
"Erythromelalgia in thrombocythemia already occurred at slightly increased platelet counts above 400 x 10(9)/l."
Establishes both the presence of thrombocytosis and the low count threshold at which symptoms occur.
Cardiovascular 2
Erythema of the extremities HP:0010783 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Erythema (HP:0010783). HP:0010783 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:3977194 SUPPORT Human Clinical
"The localized painful burning, redness, and warm congestion in the extremities could be accurately documented with thermography."
Documents the erythema and warm congestion component, objectively confirmed thermographically.
Digital ischemic necrosis Digital ischemia HP:0033402 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Digital ischemia (HP:0033402). HP:0033402 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:3977194 SUPPORT Human Clinical
"Erythromelalgia often progressed to ischemic acrocyanosis or necrosis in toes or fingers."
Documents digital ischemic necrosis as an outcome of the untreated occlusive process.
Integument 1
Acrocyanosis FREQUENT HP:0001063 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Acrocyanosis (HP:0001063). HP:0001063 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:8951772 SUPPORT Human Clinical
"Untreated erythromelalgia progressed to acrocyanosis or peripheral ischemia with necrosis in a toe or fingertip in 14 cases."
Support is PARTIAL for the FREQUENT band. Against the 31 patients in this series who had erythromelalgia the fraction is 14/31 (45%), which sits in FREQUENT — but the endpoint is a composite of acrocyanosis and necrosis, is conditioned on being untreated with no untreated denominator given, and comes from a referral series.
PMID:8951772 SUPPORT Human Clinical
"The symptoms were platelet-mediated erythromelalgia in 16 PT and 15 PV"
Establishes the 31-patient erythromelalgia denominator used above, rather than the 50-patient thrombocythemia denominator that would understate the proportion.
Constitutional 1
Acral burning pain Limb pain HP:0009763 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Limb pain (HP:0009763). HP:0009763 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:3977194 SUPPORT Human Clinical
"The localized painful burning, redness, and warm congestion in the extremities"
Describes the localized burning extremity pain that constitutes the core symptom.
Other 1
Erythromelalgia OBLIGATE HP:0032147 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Erythromelalgia (HP:0032147), qualified as temporality recurrent. HP:0032147 is a phenotype from the Human Phenotype Ontology.
Temporal: RECURRENT
Show evidence (2 references)
PMID:3977194 SUPPORT Human Clinical
"Erythromelalgia was the presenting symptom in 26 of 40 patients with thrombocythemia in its primary form or when associated with polycythemia vera."
Support is PARTIAL for the band: this quantifies how often erythromelalgia presents among referred thrombocythemia patients (26/40), which is a different denominator from the frequency of the phenotype within this disease entity. It is cited for the phenotype's association with the MPN context, not for the OBLIGATE band.
PMID:8951772 SUPPORT Human Clinical
"The symptoms were platelet-mediated erythromelalgia in 16 PT and 15 PV"
A second consecutive series records platelet-mediated erythromelalgia in 31 of 50 referred thrombocythemia patients. Again this is the MPN-population denominator, not the within-disease frequency, hence PARTIAL.
💊

Medical Actions

6
Low-dose aspirin
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: aspirin CHEBI:15365 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses aspirin, annotated with acetylsalicylic acid (CHEBI:15365). CHEBI:15365 is a therapeutic agent from Chemical Entities of Biological Interest.
The mechanism-matched treatment of MPN-associated erythromelalgia. Irreversible inhibition of platelet cyclooxygenase-1 abolishes the thromboxane-dependent platelet activation that drives arteriolar occlusion, producing complete relief of pain, restoration of microvascular circulation, normalization of shortened platelet survival, and fall of platelet-activation markers to normal. This dramatic responsiveness is the therapeutic hallmark separating MPN-associated secondary erythromelalgia from the characteristically aspirin-refractory primary (SCN9A/Nav1.7) form. Safety caveat: at very high platelet counts (roughly >1000-2000 x 10^9/L) thrombocythemia converts to a bleeding diathesis, and aspirin — while still preventing the microcirculatory disturbance — further increases the risk of serious haemorrhage.
Mechanism Target:
INHIBITS Thromboxane-Dependent Platelet Activation and Aggregation — Aspirin inhibits platelet cyclooxygenase-1, removing the thromboxane metabolites shown to be necessary for erythromelalgia to develop and thereby interrupting the platelet activation/aggregation node upstream of arteriolar occlusion.
Show evidence (2 references)
PMID:16673274 SUPPORT Human Clinical
"Inhibition of platelet cyclooxygenase-1 by aspirin is followed by relief of microvascular disturbances"
States the drug target (platelet COX-1) and the mechanistic consequence of inhibiting it.
PMID:12781799 SUPPORT Human Clinical
"Thus, cyclooxygenase metabolites are necessary for erythromelalgia to develop."
Establishes that the inhibited pathway is necessary for the disease process, licensing the INHIBITS edge.
Target Phenotypes: Erythromelalgia HP:0032147 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Erythromelalgia (HP:0032147). HP:0032147 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:3977194 SUPPORT Human Clinical
"Complete relief of pain and restoration of microvascular circulation disturbances was obtained with the cyclo-oxygenase inhibitors aspirin and indomethacin"
Documents complete symptomatic and microvascular response to cyclooxygenase inhibition.
PMID:12781799 SUPPORT Human Clinical
"Aspirin treatment of erythromelalgia in thrombocythemia patients resulted in the disappearance of the erythromelalgic, thrombotic signs and symptoms, correction of the shortened platelet survival times"
Confirms clinical and platelet-kinetic reversal on aspirin.
PMID:8951772 SUPPORT Human Clinical
"In this situation aspirin prevents erythromelalgic and microcirculatory circulation disturbances, but further increases the risk of serious bleeding complications."
Support is PARTIAL because it qualifies rather than endorses the treatment — at very high platelet counts aspirin remains effective for the microvascular disturbance but raises bleeding risk.
Indomethacin
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: indomethacin CHEBI:49662 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses indomethacin, annotated with indometacin (CHEBI:49662). CHEBI:49662 is a therapeutic agent from Chemical Entities of Biological Interest.
A second cyclooxygenase inhibitor with the same mechanism-matched efficacy, confirming that the therapeutic effect is a class effect of COX inhibition rather than an aspirin-specific property. Notably sodium salicylate and the non-COX platelet inhibitors dipyridamole, sulfinpyrazone, ticlopidine, and dazoxiben are all ineffective, which is the pharmacological argument for the thromboxane mechanism.
Mechanism Target:
INHIBITS Thromboxane-Dependent Platelet Activation and Aggregation — Indomethacin inhibits the same platelet cyclooxygenase pathway targeted by aspirin.
Show evidence (1 reference)
PMID:3977194 SUPPORT Human Clinical
"Complete relief of pain and restoration of microvascular circulation disturbances was obtained with the cyclo-oxygenase inhibitors aspirin and indomethacin, but not with sodium-salicylate or the platelet inhibitors dipyridamole, sulfinpyrazone, ticlopidine, and dazoxiben."
Indomethacin shares aspirin's efficacy while non-COX antiplatelet agents fail, establishing cyclooxygenase inhibition as the operative drug mechanism.
Show evidence (2 references)
PMID:3977194 SUPPORT Human Clinical
"Complete relief of pain and restoration of microvascular circulation disturbances was obtained with the cyclo-oxygenase inhibitors aspirin and indomethacin"
Documents complete symptomatic and microvascular relief with indomethacin alongside aspirin.
PMID:12781799 SUPPORT Human Clinical
"Complete relief from erythromelalgic and acrocyanotic pain is obtained with the cyclooxygenase inhibitors aspirin and indomethacin, but not with sodiumsalicylate, dipyridamol, sulfinpyrozone and ticlopedine."
Independently confirms indomethacin efficacy and the failure of non-COX antiplatelet agents.
Cytoreduction of the underlying myeloproliferative neoplasm
Action: cytoreductive therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is cytoreductive therapy, annotated with Chemotherapy (NCIT:C15632). NCIT:C15632 is a clinical intervention from the NCI Thesaurus. Ontology label: Chemotherapy NCIT:C15632
Treating the upstream disorder resolves the erythromelalgia: symptoms remit during cytoreduction-induced haematological remission of the thrombocythemia and recur on relapse. Contemporary cytoreductive agent selection is a matter for the MPN entries (`Polycythemia_Vera`, `Essential_Thrombocythemia`) rather than this entry; the historical evidence cited here used busulfan.
Mechanism Target:
INHIBITS Clonal Thrombocythemia in Myeloproliferative Neoplasm — Cytoreduction removes the clonal thrombocythemia that supplies the hyperreactive platelet population.
Show evidence (1 reference)
PMID:3977194 SUPPORT Human Clinical
"The erythromelalgia was alleviated during busulfan-induced remissions of thrombocythemia and its recurrence coincided with relapsing thrombocythemia."
Remission of the thrombocythemia relieves the erythromelalgia, supporting an INHIBITS edge on the upstream node.
Show evidence (2 references)
PMID:3977194 SUPPORT Human Clinical
"The erythromelalgia was alleviated during busulfan-induced remissions of thrombocythemia and its recurrence coincided with relapsing thrombocythemia."
Cytoreduction-induced haematological remission relieves the erythromelalgia, and relapse brings it back.
PMID:12781799 SUPPORT Human Clinical
"which specifically respond to low-dose aspirin or reduction of platelet counts to normal"
Support is PARTIAL — the quoted response applies to the accompanying transient ischemic manifestations, but it establishes platelet-count reduction as an effective alternative to aspirin for the platelet-mediated microvascular syndrome as a whole.
Treatment of the underlying condition in non-MPN secondary disease
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
For acquired erythromelalgia not driven by a myeloproliferative neoplasm, management is directed primarily at the underlying disease, supplemented by trigger avoidance. Aspirin is characteristically ineffective in these non-platelet-mediated forms. Note this is a statement about *cause-directed* therapy, not a claim that nothing helps symptomatically — symptomatic options with trial evidence are curated in the sibling treatment entry below.
Show evidence (3 references)
PMID:40428878 SUPPORT Human Clinical
"Secondary EM tends to be more variable in presentation, may be unilateral or localized, and treatment usually targets the underlying condition."
A 2025 systematic review states that treatment of secondary erythromelalgia usually targets the underlying condition.
PMID:29641704 SUPPORT Other
"Since there is no specific and effective treatment, control should focus on the underlying disease."
Support is PARTIAL. This 2018 narrative review's blanket "no specific and effective treatment" is used only for the cause-directed management principle; the later systematic review (PMID:40428878) reports measurable symptomatic benefit for several agents, so the unqualified negative is not adopted here.
PMID:29641704 SUPPORT Other
"The prevention of crisis is based on a strict control of triggers and promotion of preventive measures."
Supports trigger control as the preventive component of management.
Symptomatic pharmacotherapy for aspirin-unresponsive disease
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: amitriptyline CHEBI:2666 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses amitriptyline (CHEBI:2666). CHEBI:2666 is a therapeutic agent from Chemical Entities of Biological Interest. ketamine CHEBI:6121 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses ketamine (CHEBI:6121). CHEBI:6121 is a therapeutic agent from Chemical Entities of Biological Interest. lidocaine CHEBI:6456 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses lidocaine (CHEBI:6456). CHEBI:6456 is a therapeutic agent from Chemical Entities of Biological Interest. iloprost CHEBI:63916 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses iloprost (CHEBI:63916). CHEBI:63916 is a therapeutic agent from Chemical Entities of Biological Interest. misoprostol CHEBI:63610 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses misoprostol (CHEBI:63610). CHEBI:63610 is a therapeutic agent from Chemical Entities of Biological Interest.
Where the platelet-mediated COX-1 mechanism does not apply — the non-MPN acquired routes, and MPN disease inadequately controlled by aspirin — symptomatic options with controlled or cohort evidence include topical amitriptyline-ketamine, lidocaine, and the prostaglandin analogues iloprost and misoprostol. IMPORTANT EVIDENCE CAVEAT, which is why these are curated as a single node without per-agent mechanism edges: the systematic review supplying this evidence pooled 120 patients across primary, idiopathic and secondary erythromelalgia and did NOT report outcomes stratified by aetiology, so efficacy specific to secondary disease is not established. Misoprostol in particular caused severe gastrointestinal toxicity.
Target Phenotypes: Limb pain HP:0009763 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Limb pain (HP:0009763). HP:0009763 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:40428878 SUPPORT Human Clinical
"About 75% of the patients reported pain relief with topical amitriptyline-ketamine, while lidocaine reduced nociceptive feelings in a dose-dependent manner."
Support is PARTIAL because the pooled cohort mixes primary, idiopathic and secondary erythromelalgia and is not stratified by aetiology, so the response rate cannot be attributed to secondary disease specifically.
PMID:40428878 SUPPORT Human Clinical
"Iloprost and misoprostol exhibited notable benefits in cooling scores, sympathetic dysfunction, and EM severity compared to placebos."
Placebo-controlled benefit for the two prostaglandin analogues, again in a mixed-aetiology population, hence PARTIAL.
PMID:40428878 SUPPORT Human Clinical
"adverse events ranged from mild gastrointestinal symptoms to severe complications such as disability and depression, requiring careful monitoring"
Documents the tolerability burden that qualifies these symptomatic options.
Chemical lumbar sympathectomy
Action: chemical lumbar sympathectomyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is chemical lumbar sympathectomy, annotated with Therapeutic Procedure (NCIT:C49236). NCIT:C49236 is a clinical intervention from the NCI Thesaurus. Ontology label: Therapeutic Procedure NCIT:C49236
An invasive procedural option for refractory disease, reported to give sustained pain reduction with mild thigh pain as the common side effect. Carried as a sibling of the symptomatic-pharmacotherapy node under the SAME mixed-aetiology caveat: the systematic review supplying this evidence pooled 120 patients across primary, idiopathic and secondary erythromelalgia (13 of them receiving CLS) and did not stratify outcomes by aetiology, so efficacy in secondary disease is not established. Long-term outcomes are additionally underreported, and relapse is described in patients carrying SCN9A variants — a caveat belonging to the primary form, noted here only because it is inseparable from the pooled cohort. Term note: NCIT has no verifiable term for sympathectomy specifically, so the generic verified action term is used with a precise `preferred_term`; the procedure is a percutaneous chemical neurolysis rather than open surgery, though `SURGERY` is the closest available `therapeutic_modality` bucket for an invasive procedure.
Target Phenotypes: Limb pain HP:0009763 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Limb pain (HP:0009763). HP:0009763 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40428878 SUPPORT Human Clinical
"observed significant pain reduction with CLS, with mild thigh pain as a side effect."
Support is PARTIAL — significant pain reduction is reported, but within a mixed-aetiology pooled review that does not separate secondary from primary/idiopathic disease.
PMID:40428878 SUPPORT Human Clinical
"Despite encouraging short-term results, long-term outcomes after CLS remain underreported and variable."
Qualifies the procedure: encouraging short-term results but underreported and variable long-term outcomes, which is why this is curated as an option rather than a recommendation.
🌍

Environmental Factors

1
Limb warming, exercise, and dependency as attack precipitants
Erythromelalgic attacks are provoked by warmth and by anything that raises acral blood flow or venous pressure — exercise, physical activity, limb dependency, prolonged standing, and occlusive footwear — and are relieved by cooling and elevation. These are precipitants of the flare, not causes of the underlying disorder, so they are modeled as EXACERBATES on the flare node rather than as a trigger of the upstream mechanism. Note the therapeutic hazard shared with the primary form: patients self-treat by prolonged cold-water immersion, which causes skin maceration and secondary tissue injury.
Show evidence (1 reference)
PMID:40428878 SUPPORT Human Clinical
"Common relievers involve cooling methods such as local skin cooling or ice water immersion."
Documents cooling as the characteristic reliever, the counterpart of the warming trigger.
Mechanism Target:
EXACERBATES Episodic Acral Burning Pain, Erythema, and Warmth — Heat and exertion precipitate the erythromelalgic attack; cooling relieves it.
Show evidence (2 references)
PMID:40428878 SUPPORT Human Clinical
"Triggers for symptoms included warmth, exercise, dependency, tight footwear or gloves, physical activity, immersion, and emotional stress."
Enumerates the attack precipitants recorded across the systematic review's patient cohorts.
PMID:32491719 SUPPORT Other
"The episodes are typically precipitated by exercise and relieved by cooling the affected parts."
States the precipitation-by-exertion and relief-by-cooling pattern that defines the flare.
🔬

Biochemical Markers

4
Beta-thromboglobulin (Elevated)
Show evidence (1 reference)
PMID:8883266 SUPPORT Human Clinical
"As compared with asymptomatic ET patients and control subjects erythromelalgia was characterized by significantly higher beta-TG and TM levels but no significant differences were detected in either F1 + 2 or TDP levels."
Beta-thromboglobulin and thrombomodulin are selectively elevated in symptomatic patients while thrombin-generation markers are not, marking platelet activation and endothelial injury without coagulation activation.
Thrombomodulin (Elevated)
Show evidence (1 reference)
PMID:8883266 SUPPORT Human Clinical
"Treatment of erythromelalgia with aspirin resulted in disappearance of erythromelalgic signs and symptoms, which was paralleled by a significant decrease of beta-TG and TM levels."
Links normalization of the endothelial-damage and platelet-activation markers to clinical remission on aspirin.
Platelet survival time (Shortened)
Show evidence (2 references)
PMID:7792731 SUPPORT Human Clinical
"The mean platelet survival time of the erythromelalgia patients was 4.2 +/- 0.2 days, which is significantly decreased as compared with asymptomatic thrombocythemia patients (6.6 +/- 0.3 days, p < 0.001) and patients with reactive thrombocytosis (8.0 +/- 0.4 days, p < 0.001)."
Quantifies shortened platelet survival specifically in symptomatic erythromelalgia versus two comparator groups.
PMID:7792731 SUPPORT Human Clinical
"Treatment of erythromelalgia with aspirin increased the mean platelet survival time from 4.0 +/- 0.3 days to 6.9 +/- 0.4 days (p < 0.001)"
Aspirin reverses the shortened platelet survival, confirming COX-dependent platelet consumption as the operative process.
Urinary thromboxane B2 (Elevated)
Show evidence (1 reference)
PMID:12781799 SUPPORT Human Clinical
"a significant reduction of the increased levels of beta-TG, PF4, TM and urinary TxB2 excretion to normal"
Aspirin normalizes urinary thromboxane B2 alongside the other platelet-activation markers.
🔬

Diagnosis

3
Evaluation for an underlying myeloproliferative neoplasm
Because erythromelalgia is regarded as a pathognomonic microvascular complication of essential thrombocythemia and polycythemia vera — and frequently its presenting manifestation — a new diagnosis of erythromelalgia warrants haematological evaluation for an occult MPN, including a platelet count that may be only modestly elevated.
Results: Thrombocytosis (possibly only slightly above 400 x 10^9/L) with an MPN diagnosis supports platelet-mediated secondary erythromelalgia.
Show evidence (1 reference)
PMID:3977194 SUPPORT Human Clinical
"Erythromelalgia was the presenting symptom in 26 of 40 patients with thrombocythemia in its primary form or when associated with polycythemia vera."
Erythromelalgia is the presenting symptom in most such patients, justifying MPN evaluation on presentation.
Skin punch biopsy of an affected area
Histopathology of affected acral skin demonstrates the characteristic arteriolar inflammation, fibromuscular intimal proliferation, and platelet-rich thrombotic occlusions that distinguish platelet-mediated secondary erythromelalgia from the primary neuropathic form.
Results: Arteriolar inflammation, fibromuscular intimal proliferation, and thrombotic occlusion.
Show evidence (1 reference)
PMID:3977194 SUPPORT Human Clinical
"Skin punch biopsy samples taken from the affected areas showed typical arteriolar inflammation, fibromuscular intima proliferation, and thrombotic occlusions."
Establishes the diagnostic histopathological findings on skin punch biopsy.
Therapeutic response to aspirin as a diagnostic discriminator
The dramatic, complete, and sustained response of platelet-mediated erythromelalgia to a cyclooxygenase inhibitor is itself diagnostically informative: the historical Drenth-Michiels classification of red, burning extremities was built on aspirin responsiveness, separating aspirin-responsive thrombocythemic erythromelalgia from the aspirin-resistant primary and other secondary forms.
Results: Complete relief of pain with aspirin supports the platelet-mediated (MPN-associated) form.
Show evidence (1 reference)
PMID:32491719 SUPPORT Other
"The term erythromelalgia and erythermalgia were differentiated on the basis of responsiveness to aspirin by Drenth and Michiels"
Documents aspirin responsiveness as the historical basis for discriminating these entities.
📊

Prevalence

1
Olmsted County, Minnesota, USA (population-based, 1976-2005)
Annual Incidence 0.2 per 100,000 (0.02–0.4) Rare
Population-based age- and sex-adjusted incidence of secondary erythromelalgia from the Rochester Epidemiology Project (overall erythromelalgia incidence 1.3/100,000/yr; primary 1.1/100,000/yr). In this study "secondary" was defined by a coexisting myeloproliferative disorder, or attribution to another cause such as medications, HIV, or mushroom poisoning. The confidence interval is wide and the authors note the small sample size as a limitation.
Show evidence (1 reference)
PMID:18713229 SUPPORT Human Clinical
"The incidence of primary and secondary erythromelalgia was 1.1 (0.7-1.5) and 0.2 (0.02-0.4) per 100,000 people per year, respectively."
Provides the population-based annual incidence estimate for secondary erythromelalgia.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Secondary Erythromelalgia:

Primary erythermalgia MONDO:0007571
Overlapping Features The principal differential. Primary/inherited erythromelalgia is an autosomal dominant SCN9A (Nav1.7) gain-of-function channelopathy of nociceptors, characteristically bilateral and symmetric, and characteristically refractory to aspirin — the mechanistic and therapeutic mirror image of the platelet-mediated secondary form modeled here. Curated separately as `Primary_Erythermalgia`.
Show evidence (3 references)
PMID:8203771 SUPPORT Human Clinical
"the authors discern three distinct types of red, congested, and burning extremities that need to be distinguished for effective treatment according to their etiology: erythromelalgia in thrombocythemia, primary erythermalgia, and secondary erythermalgia"
Establishes that thrombocythemic erythromelalgia and primary erythermalgia are distinct clinicopathologic entities requiring different treatment.
PMID:32491719 SUPPORT Other
"Primary erythermalgia: Refers to an idiopathic or inherited disorder. Also called aspirin-resistant erythermalgia of unknown origin."
Documents the aspirin resistance of primary erythermalgia, the therapeutic discriminator from the MPN-associated form.
PMID:30609105 SUPPORT Other
"recent discoveries of the genetic mutations that now define primary erythromelalgia, as opposed to secondary erythromelalgia"
States that genetic mutations define the primary form in contradistinction to the secondary form.
Superficial thrombophlebitis
Overlapping Features Painful red, warm, indurated erythromelalgic "hot spots" on the skin of the upper legs in thrombocythemia are readily misdiagnosed as superficial thrombophlebitis, which would be treated quite differently.
Show evidence (1 reference)
PMID:8951772 SUPPORT Human Clinical
"Painful red, warm and indurated erythromelalgic hot spots in the skin of the upper legs were misdiagnosed as superficial thrombophelebitis in 5 PT and 2 PV patients."
Documents this specific misdiagnosis in 7 of 50 thrombocythemia patients.
{ }

Source YAML

click to show 
name: Secondary Erythromelalgia
creation_date: "2026-08-17T00:00:00Z"
description: >-
  Secondary (acquired) erythromelalgia is erythromelalgia arising in the context
  of an identifiable underlying disorder rather than from an inherited
  sodium-channel lesion. Its best-characterized and best-evidenced form is
  the erythromelalgia of the myeloproliferative neoplasms (MPN) — essential
  thrombocythemia and polycythemia vera — where the mechanism is not nociceptor
  channelopathy but platelet-mediated arteriolar inflammation and thrombotic
  occlusion of the acral microvasculature. Skin punch biopsies from affected
  areas show arteriolar inflammation, fibromuscular intimal proliferation, and
  platelet-rich thrombotic occlusions; platelet survival is shortened, platelet
  activation markers are elevated, and the entire syndrome is abolished by
  cyclooxygenase inhibition. Other acquired routes — autoimmune connective-tissue
  disease, small-fiber peripheral neuropathy, and drug exposure — are recognized
  but far less mechanistically resolved. This entry is the acquired sibling of
  `Primary_Erythermalgia` (SCN9A/Nav1.7 gain-of-function) and sits beneath the
  umbrella entry `erythromelalgia`; the two are distinguished mechanistically
  (platelet-microvascular versus neuronal-channelopathy) and therapeutically (the
  dramatic aspirin responsiveness of MPN-associated disease versus the
  characteristic aspirin refractoriness of the primary form). The underlying MPN
  pathophysiology itself is curated in `Polycythemia_Vera` and
  `Essential_Thrombocythemia` and is deliberately not re-derived here.
category: Complex
parents:
- disease
disease_term:
  preferred_term: secondary erythromelalgia
  term:
    id: MONDO:0035149
    label: secondary erythromelalgia
mappings:
  icd10cm_mappings:
  - term:
      id: ICD10CM:I73.8
      label: Other specified peripheral vascular diseases
    mapping_predicate: skos:broadMatch
    mapping_source: MONDO:0035149
    mapping_justification: >-
      MONDO:0035149 carries ICD10CM:I73.8 as a cross-reference. The predicate is broadMatch, not
      exactMatch: I73.8 is a residual "other specified peripheral vascular diseases" bucket that
      does not distinguish primary from secondary erythromelalgia, so an ICD-10-CM-coded cohort
      cannot be used as a case definition for this entry.
notes: >-
  Deliberate non-conformance to the `thrombogenesis` module. The acral thrombi of
  MPN-associated erythromelalgia are platelet- and von Willebrand factor-rich with
  only weak fibrin staining, and develop despite therapeutic anticoagulation, with
  no rise in prothrombin fragment 1+2 (PMID:8883266) — i.e. thrombin generation is
  not required. The `thrombogenesis` module explicitly scopes out "VWF-platelet
  microangiopathy ... unless a distinct conventional thrombin/fibrin thrombosis
  branch is explicitly evidenced", and no such branch is evidenced here, so no
  `conforms_to` edge is asserted. This is recorded rather than silently omitted
  because the disease looks superficially like a thrombogenesis conformer.


  `datasets:` is intentionally empty. `just discover-datasets` returns no GEO
  candidates, and the obvious relaxations are both unsafe here: this syndrome has
  no causal gene of its own, so a gene-keyed search has nothing to key on, and
  searching the underlying myeloproliferative neoplasms would return datasets that
  belong to `Polycythemia_Vera` / `Essential_Thrombocythemia` rather than to this
  entry. Adding those would be Named Entity Confusion reached through dataset
  search, so nothing is recorded.


  `clinical_trials:` is likewise intentionally empty. The interventional trials in
  erythromelalgia recruit primary/inherited or idiopathic disease and explicitly
  exclude patients whose extremity pain has another cause — the EASE study of ATX01
  topical amitriptyline 15% (NCT05917912, AlgoTherapeutix, 14 participants), the
  burst spinal-cord-stimulation study (NCT04039633, St. Olavs Hospital, 6
  participants), and the Nav1.7-targeted agent studies (NCT01090622, NCT01486446,
  NCT01769274). None of them enrol secondary erythromelalgia, so listing them here
  would misattribute trial evidence to this entity. The two lead identifiers were
  checked against the ClinicalTrials.gov API directly, not only against the
  deep-research report, because identifiers inside free-text `notes:` are not
  reference-validated by `just validate-disorders`.
pathophysiology:
- name: Clonal Thrombocythemia in Myeloproliferative Neoplasm
  biological_scale: ORGANISM
  description: >-
    The upstream trigger of MPN-associated erythromelalgia is the clonal
    thrombocythemia of essential thrombocythemia or polycythemia vera, which
    supplies a population of qualitatively abnormal, hyperactivatable platelets.
    The dependence is causal rather than merely associative: erythromelalgia
    remits during cytoreduction-induced haematological remission and recurs when
    the thrombocythemia relapses. Notably the threshold is low — symptoms occur at
    platelet counts only slightly above normal — so absolute platelet mass is not
    the determinant. The clonal driver biology itself (JAK2 V617F and the
    haematopoietic consequences) is curated in `Polycythemia_Vera` and
    `Essential_Thrombocythemia`.
  cell_types:
  - preferred_term: platelet
    term:
      id: CL:0000233
      label: platelet
  - preferred_term: megakaryocyte
    term:
      id: CL:0000556
      label: megakaryocyte
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The erythromelalgia was alleviated during busulfan-induced remissions of thrombocythemia and its recurrence coincided with relapsing thrombocythemia."
    explanation: >-
      Remission-and-relapse concordance with the underlying thrombocythemia establishes
      the MPN as the causal upstream driver rather than a coincidental association.
  - reference: PMID:9263352
    reference_title: 'Erythromelalgia: a pathognomonic microvascular thrombotic complication in essential thrombocythemia and polycythemia vera.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Erythromelalgia is a characteristic thrombotic complication in patients with the myeloproliferative disorders, essential thrombocythemia and polycythemia vera."
    explanation: >-
      Identifies the two myeloproliferative neoplasms that constitute the principal underlying
      disorders of this secondary form. Classified OTHER because this is a narrative minireview
      summarizing the authors' prior work rather than a report of primary data.
  - reference: PMID:8951772
    reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Erythromelalgia in thrombocythemia already occurred at slightly increased platelet counts above 400 x 10(9)/l."
    explanation: >-
      Symptoms arise at only slightly elevated platelet counts, indicating that qualitative
      platelet hyperreactivity rather than absolute platelet mass drives the mechanism.
  downstream:
  - target: Thromboxane-Dependent Platelet Activation and Aggregation
    description: The clonal platelet population undergoes intravascular cyclooxygenase-dependent activation and aggregation.
    evidence:
    - reference: PMID:8883266
      reference_title: Erythromelalgia in essential thrombocythemia is characterized by platelet activation and endothelial cell damage but not by thrombin generation.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Our data suggest that erythromelalgia is caused by the intravascular activation and aggregation of platelets with subsequent sludging or occlusion of the acral arterial microvasculature."
      explanation: Links the thrombocythemic platelet population to intravascular platelet activation and aggregation.
- name: Thromboxane-Dependent Platelet Activation and Aggregation
  biological_scale: CELLULAR
  description: >-
    Circulating MPN platelets undergo intravascular activation and aggregation in
    the acral microcirculation. The process is strictly cyclooxygenase-metabolite
    dependent: it is abolished by aspirin and indomethacin but not by
    sodium salicylate or by non-COX platelet inhibitors (dipyridamole,
    sulfinpyrazone, ticlopidine, dazoxiben). In vivo activation is measurable as
    elevated beta-thromboglobulin, platelet factor 4, thrombomodulin, and urinary
    thromboxane B2, together with a markedly shortened platelet survival time that
    aspirin normalizes. Critically, thrombin generation is NOT required — prothrombin
    fragment 1+2 and fibrin degradation products are unchanged, and the lesions
    develop despite heparin or coumarin anticoagulation.
  cell_types:
  - preferred_term: platelet
    term:
      id: CL:0000233
      label: platelet
  biological_processes:
  - preferred_term: platelet activation
    modifier: INCREASED
    term:
      id: GO:0030168
      label: platelet activation
  - preferred_term: platelet aggregation
    modifier: INCREASED
    term:
      id: GO:0070527
      label: platelet aggregation
  - preferred_term: prostanoid (thromboxane) biosynthesis
    modifier: INCREASED
    term:
      id: GO:0046457
      label: prostanoid biosynthetic process
  molecular_functions:
  - preferred_term: platelet cyclooxygenase-1 activity
    term:
      id: GO:0004666
      label: prostaglandin-endoperoxide synthase activity
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Complete relief of pain and restoration of microvascular circulation disturbances was obtained with the cyclo-oxygenase inhibitors aspirin and indomethacin, but not with sodium-salicylate or the platelet inhibitors dipyridamole, sulfinpyrazone, ticlopidine, and dazoxiben."
    explanation: >-
      The pharmacological dissection — COX inhibitors work, other antiplatelet agents do not —
      establishes cyclooxygenase metabolites as mechanistically necessary.
  - reference: PMID:12781799
    reference_title: 'Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thus, cyclooxygenase metabolites are necessary for erythromelalgia to develop."
    explanation: States the necessity of cyclooxygenase metabolites explicitly.
  - reference: PMID:12781799
    reference_title: 'Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "significant higher levels of platelet activation markers beta-thromboglobulin, thrombomoduline and increased urinary thromboxane B2 excretion in thrombocythemia patients suffering from erythromelalgia"
    explanation: Quantifies in vivo platelet activation and thromboxane generation specifically in symptomatic patients.
  - reference: PMID:8883266
    reference_title: Erythromelalgia in essential thrombocythemia is characterized by platelet activation and endothelial cell damage but not by thrombin generation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our data suggest that erythromelalgia is caused by the intravascular activation and aggregation of platelets with subsequent sludging or occlusion of the acral arterial microvasculature."
    explanation: Directly states intravascular platelet activation and aggregation as the causal mechanism.
  - reference: PMID:8883266
    reference_title: Erythromelalgia in essential thrombocythemia is characterized by platelet activation and endothelial cell damage but not by thrombin generation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The generation of thrombin appears not to be essential for the formation of these platelet thrombi, thereby giving a plausible explanation for the inefficacy of coumadin derivatives and heparin in the prevention and treatment of erythromelalgia in essential thrombocythemia."
    explanation: >-
      Establishes the thrombin-independence of the mechanism — the basis for this entry's
      deliberate non-conformance to the thrombin/fibrin `thrombogenesis` module.
  - reference: PMID:7792731
    reference_title: 'Platelet consumption in thrombocythemia complicated by erythromelalgia: reversal by aspirin.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The increased platelet consumption in erythromelalgia is attributed to the formation of platelet thrombi in the arterial microvasculature."
    explanation: Radiolabelled platelet-survival kinetics independently confirm ongoing platelet consumption in microvascular thrombi.
  downstream:
  - target: Arteriolar Inflammation and Fibromuscular Intimal Proliferation
    description: Activated platelets and their released mediators injure and remodel the arteriolar wall.
    evidence:
    - reference: PMID:12781799
      reference_title: 'Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Local platelet consumption in erythromelalgic areas became evident by the demonstration of arteriolar fibromuscular intimal proliferation and occlusions by platelet-rich thrombi in skin biopsies"
      explanation: Ties local platelet consumption directly to the arteriolar intimal-proliferative lesion.
  - target: Acral Arteriolar Microvascular Occlusion
    description: Platelet aggregates sludge and occlude the acral arterial microvasculature.
    evidence:
    - reference: PMID:8883266
      reference_title: Erythromelalgia in essential thrombocythemia is characterized by platelet activation and endothelial cell damage but not by thrombin generation.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "intravascular activation and aggregation of platelets with subsequent sludging or occlusion of the acral arterial microvasculature"
      explanation: States the causal step from platelet aggregation to acral microvascular occlusion.
- name: Arteriolar Inflammation and Fibromuscular Intimal Proliferation
  biological_scale: TISSUE
  description: >-
    Skin punch biopsies taken from erythromelalgic areas show a distinctive
    arteriolar lesion — inflammation of the arteriolar wall with fibromuscular
    proliferation of the intima — accompanying the thrombotic occlusions. This
    inflammatory and proliferative wall response, together with the elevated
    thrombomodulin indicating endothelial injury, distinguishes the lesion from a
    bland intraluminal clot and is what makes "platelet-mediated arteriolar
    inflammation" rather than simple thrombosis the accurate description.
  cell_types:
  - preferred_term: arteriolar endothelial cell
    term:
      id: CL:0000115
      label: endothelial cell
  - preferred_term: arteriolar smooth muscle cell
    term:
      id: CL:0000192
      label: smooth muscle cell
  biological_processes:
  - preferred_term: inflammatory response
    modifier: INCREASED
    term:
      id: GO:0006954
      label: inflammatory response
  - preferred_term: smooth muscle cell proliferation
    modifier: INCREASED
    term:
      id: GO:0048659
      label: smooth muscle cell proliferation
  locations:
  - preferred_term: arteriole
    term:
      id: UBERON:0001980
      label: arteriole
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Skin punch biopsy samples taken from the affected areas showed typical arteriolar inflammation, fibromuscular intima proliferation, and thrombotic occlusions."
    explanation: Direct histopathological demonstration of the arteriolar inflammatory and intimal-proliferative lesion in affected skin.
  - reference: PMID:12781799
    reference_title: 'Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the demonstration of arteriolar fibromuscular intimal proliferation and occlusions by platelet-rich thrombi in skin biopsies"
    explanation: Independently restates the arteriolar intimal-proliferative and platelet-rich occlusive histopathology.
  downstream:
  - target: Acral Arteriolar Microvascular Occlusion
    description: Intimal proliferation narrows the arteriolar lumen and compounds platelet-driven occlusion.
    evidence:
    - reference: PMID:3977194
      reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Skin punch biopsy samples taken from the affected areas showed typical arteriolar inflammation, fibromuscular intima proliferation, and thrombotic occlusions."
      explanation: The inflammatory/intimal-proliferative change and the thrombotic occlusion are demonstrated together in the same affected-skin biopsies.
- name: Acral Arteriolar Microvascular Occlusion
  biological_scale: TISSUE
  description: >-
    The convergent lesion is occlusion of acral arterioles by platelet-rich,
    von Willebrand factor-positive thrombi with only weak fibrin content. The
    resulting acral perfusion disturbance is the immediate substrate of the
    erythromelalgic flare and, if unrelieved, of progressive digital ischemia. The
    VWF-rich, fibrin-poor composition of these thrombi is the histological
    counterpart of the biochemical finding that thrombin generation is dispensable.
  locations:
  - preferred_term: arteriole
    term:
      id: UBERON:0001980
      label: arteriole
  evidence:
  - reference: PMID:8883266
    reference_title: Erythromelalgia in essential thrombocythemia is characterized by platelet activation and endothelial cell damage but not by thrombin generation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histopathologic and immunohistochemical analysis of biopsies derived from erythromelalgic skin areas of 2 ET patients showed that erythromelalgic thrombi stained positively for von Willebrand factor opposed to only a weak fibrin staining."
    explanation: >-
      Immunohistochemistry establishes the VWF-rich, fibrin-poor composition of the occluding
      thrombi, distinguishing them from conventional fibrin-platelet thrombi.
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "platelet-mediated inflammatory and occlusive arteriolar changes play a part in the etiology of erythromelalgia"
    explanation: Summarizes occlusive arteriolar change as the operative lesion in the aetiology of the syndrome.
  downstream:
  - target: Episodic Acral Burning Pain, Erythema, and Warmth
    description: Acral microvascular occlusion and the accompanying congestion produce the erythromelalgic attack.
    evidence:
    - reference: PMID:3977194
      reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Complete relief of pain and restoration of microvascular circulation disturbances was obtained with the cyclo-oxygenase inhibitors aspirin and indomethacin"
      explanation: >-
        Pain relief and restoration of the microvascular circulation move together under COX inhibition,
        supporting the microvascular disturbance as the proximate cause of the flare.
  - target: Progression to Acrocyanosis and Digital Ischemic Necrosis
    description: Untreated, sustained occlusion progresses to fixed acral ischemia.
    evidence:
    - reference: PMID:8951772
      reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Untreated erythromelalgia progressed to acrocyanosis or peripheral ischemia with necrosis in a toe or fingertip in 14 cases."
      explanation: The untreated occlusive process progresses to acrocyanosis and acral necrosis in a defined fraction of patients.
- name: Episodic Acral Burning Pain, Erythema, and Warmth
  biological_scale: ORGANISM
  description: >-
    The clinical expression is the erythromelalgic attack: localized burning pain
    with redness and warm congestion of the distal extremities, documentable by
    thermography, most often in the forefoot sole and toes and less often in the
    fingertips or palm. Unlike the bilaterally symmetric flares of the primary
    form, secondary attacks are frequently asymmetric or unilateral, and
    erythromelalgic "hot spots" on the legs can be misread as superficial
    thrombophlebitis. No `biological_processes` are bound to this node: the obvious
    candidate (vasodilation) is not measured by any cited study and would sit
    awkwardly against this entry's occlusive model, in which the red, warm skin
    accompanies platelet-rich arteriolar obstruction rather than simple vasodilation.
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The localized painful burning, redness, and warm congestion in the extremities could be accurately documented with thermography."
    explanation: Describes the flare phenotype and its objective thermographic correlate.
  - reference: PMID:8951772
    reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Erythromelalgia was localized in the forefoot sole and toes in 28, the fingertips in 9, the handpalm in 2."
    explanation: Quantifies the acral, foot-predominant anatomical distribution of attacks in a 50-patient thrombocythemia series.
  - reference: PMID:32491719
    reference_title: Erythromelalgia.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Although erythromelalgia is typically bilateral, it can present unilaterally, especially in secondary cases."
    explanation: >-
      Supports asymmetric/unilateral presentation as a feature that clinically distinguishes
      secondary from the characteristically bilateral primary form.
- name: Progression to Acrocyanosis and Digital Ischemic Necrosis
  biological_scale: TISSUE
  description: >-
    When the platelet-mediated occlusive process is not interrupted, the reversible
    erythromelalgic flare progresses to fixed acral ischemia: acrocyanosis and
    then frank ischemic necrosis or gangrene of toes or fingertips. This
    ischemic-progression arm is a mechanistically distinct outcome from the
    self-inflicted cold-immersion tissue injury that dominates complications in the
    primary form, and it is the reason MPN-associated erythromelalgia is treated as
    a thrombotic complication rather than purely a pain syndrome.
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Erythromelalgia often progressed to ischemic acrocyanosis or necrosis in toes or fingers."
    explanation: Documents progression from the reversible flare to fixed acral ischemic tissue loss.
  - reference: PMID:8951772
    reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Untreated erythromelalgia progressed to acrocyanosis or peripheral ischemia with necrosis in a toe or fingertip in 14 cases."
    explanation: Quantifies ischemic progression in 14 of 50 thrombocythemia patients when erythromelalgia was left untreated.
- name: Non-Platelet Acquired Routes (Neuropathic, Autoimmune, Drug-Induced)
  biological_scale: ORGANISM
  mechanism_confidence: PROVISIONAL
  description: >-
    Beyond the myeloproliferative neoplasms, erythromelalgia is reported secondary
    to small-fiber peripheral neuropathy, autoimmune connective-tissue disease, and
    drug exposure. These routes are recognised clinically but are far less
    mechanistically resolved than the MPN arm: combined neural and vascular
    abnormalities are invoked rather than a single demonstrated lesion, and
    critically these forms do NOT share the aspirin responsiveness of the
    platelet-mediated arm, which is why the historical Drenth-Michiels
    classification separated aspirin-resistant "secondary erythermalgia" from
    aspirin-responsive thrombocythemic erythromelalgia. Curated here as a
    deliberately low-resolution node rather than a speculative mechanism chain.
  evidence:
  - reference: PMID:40428878
    reference_title: 'Comparative Efficacy and Tolerability of Treatments for Erythromelalgia: A Systematic Review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is often linked to underlying conditions such as myeloproliferative disorders (e.g., essential thrombocythemia, polycythemia vera), autoimmune diseases, infections, tumors, or medication use"
    explanation: >-
      Enumerates the acquired etiologies named in this node — autoimmune disease, infection,
      neoplasia and drug exposure alongside the myeloproliferative neoplasms.
  - reference: PMID:18713229
    reference_title: 'Incidence of erythromelalgia: a population-based study in Olmsted County, Minnesota.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "if the erythromelalgia was thought to be attributable to another cause such as medications, human immunodeficiency virus, or mushroom poisoning"
    explanation: >-
      A population-based study's own case definition independently names the drug, infection and
      toxin routes as recognized non-MPN causes of secondary erythromelalgia.
  - reference: PMID:15075045
    reference_title: Erythromelalgia.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "secondary, which is associated with myeloproliferative disorders-related thrombocythemia, polycythemia, collagen-vascular diseases, diabetes mellitus, peripheral neuropathy, autoimmune and infectious diseases, and use of certain medicaments"
    explanation: >-
      Names the acquired associations modeled by this node — collagen-vascular disease, diabetes
      mellitus, peripheral neuropathy, autoimmune and infectious disease, and drug exposure —
      alongside the myeloproliferative route curated separately above.
  - reference: PMID:30609105
    reference_title: Review of primary and secondary erythromelalgia.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "secondary erythromelalgia, which is often associated with underlying medical disorders"
    explanation: >-
      Establishes the defining feature of the secondary form — association with an underlying
      medical disorder — as distinct from the genetically defined primary form.
  - reference: PMID:29641704
    reference_title: 'Erythromelalgia: a cutaneous manifestation of neuropathy?'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Primary erythromelalgia is an autosomal dominant inherited disorder, while secondary is associated with myeloproliferative diseases, among others. In its etiopathogenesis, there are neural and vascular abnormalities that can be combined."
    explanation: >-
      Support is PARTIAL — the review asserts combined neural and vascular contributions to
      secondary disease without resolving a specific lesion for the non-MPN routes.
  - reference: PMID:32491719
    reference_title: Erythromelalgia.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Secondary erythermalgia: Aspirin resistant and associated with different medical conditions."
    explanation: >-
      States that the non-thrombocythemic acquired forms are aspirin resistant, separating them
      pharmacologically from the platelet-mediated MPN arm modeled above.
  downstream:
  - target: Episodic Acral Burning Pain, Erythema, and Warmth
    description: These acquired routes converge on the same clinical flare phenotype by mechanisms that remain incompletely defined.
    evidence:
    - reference: PMID:29641704
      reference_title: 'Erythromelalgia: a cutaneous manifestation of neuropathy?'
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Erythromelalgia is an infrequent episodic acrosyndrome affecting mainly both lower limbs symmetrically with the classic triad of erythema, warmth and burning pain."
      explanation: >-
        Support is PARTIAL — the review establishes that the acquired routes present with the same
        clinical triad, but does not resolve the causal steps linking them to it.
phenotypes:
- name: Erythromelalgia
  category: Clinical
  frequency: OBLIGATE
  description: >-
    The defining phenotype: episodic redness, warmth, and burning pain of the
    distal extremities. `OBLIGATE` because this phenotype *is* the disease — every
    patient with secondary erythromelalgia has it by definition, so the band is a
    statement about the entity rather than an observed proportion. Note the
    distinction from the separate question of how often erythromelalgia occurs
    *among MPN patients*: that proportion is curated on the MPN entries
    (`Polycythemia_Vera`, `Essential_Thrombocythemia`), which record `OCCASIONAL`
    from Orphanet. The two hospital series cited below report far higher fractions
    (26/40 = 65%; 31/50 = 62%), but those come from a hematology group that
    specialized in this syndrome and are referral-biased; they are cited here for
    the disease-phenotype association and the MPN link, NOT as the basis for this
    band.
  phenotype_term:
    preferred_term: Erythromelalgia
    term:
      id: HP:0032147
      label: Erythromelalgia
    temporality: RECURRENT
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Erythromelalgia was the presenting symptom in 26 of 40 patients with thrombocythemia in its primary form or when associated with polycythemia vera."
    explanation: >-
      Support is PARTIAL for the band: this quantifies how often erythromelalgia presents among
      referred thrombocythemia patients (26/40), which is a different denominator from the
      frequency of the phenotype within this disease entity. It is cited for the phenotype's
      association with the MPN context, not for the OBLIGATE band.
  - reference: PMID:8951772
    reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms were platelet-mediated erythromelalgia in 16 PT and 15 PV"
    explanation: >-
      A second consecutive series records platelet-mediated erythromelalgia in 31 of 50 referred
      thrombocythemia patients. Again this is the MPN-population denominator, not the
      within-disease frequency, hence PARTIAL.
- name: Acral burning pain
  category: Neurologic
  description: >-
    Severe localized burning pain of the affected distal extremity during attacks —
    the dominant symptomatic burden and, in MPN-associated disease, completely and
    rapidly abolished by cyclooxygenase inhibition.
  phenotype_term:
    preferred_term: Limb pain
    term:
      id: HP:0009763
      label: Limb pain
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The localized painful burning, redness, and warm congestion in the extremities"
    explanation: Describes the localized burning extremity pain that constitutes the core symptom.
- name: Erythema of the extremities
  category: Dermatologic
  description: Visible redness and warm congestion of the affected acral skin during attacks.
  phenotype_term:
    preferred_term: Erythema
    term:
      id: HP:0010783
      label: Erythema
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The localized painful burning, redness, and warm congestion in the extremities could be accurately documented with thermography."
    explanation: Documents the erythema and warm congestion component, objectively confirmed thermographically.
- name: Acrocyanosis
  category: Vascular
  frequency: FREQUENT
  description: >-
    Progression of the untreated microvascular occlusive process from red, warm
    congestion to dusky cyanotic acral discoloration, marking the transition from a
    reversible flare to established acral ischemia. Band caveats, since the source
    figure is easy to misread: the 14 cases below are drawn from the 31 patients in
    that series who actually had erythromelalgia (not from all 50 thrombocythemia
    patients), giving 14/31 = 45%; the endpoint is *composite* ("acrocyanosis OR
    peripheral ischemia with necrosis"), so acrocyanosis alone cannot be separated
    out; the figure applies to *untreated* disease, and the untreated denominator is
    not reported; and the cohort is an MPN-referred hospital series.
  phenotype_term:
    preferred_term: Acrocyanosis
    term:
      id: HP:0001063
      label: Acrocyanosis
  evidence:
  - reference: PMID:8951772
    reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Untreated erythromelalgia progressed to acrocyanosis or peripheral ischemia with necrosis in a toe or fingertip in 14 cases."
    explanation: >-
      Support is PARTIAL for the FREQUENT band. Against the 31 patients in this series who had
      erythromelalgia the fraction is 14/31 (45%), which sits in FREQUENT — but the endpoint is a
      composite of acrocyanosis and necrosis, is conditioned on being untreated with no untreated
      denominator given, and comes from a referral series.
  - reference: PMID:8951772
    reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms were platelet-mediated erythromelalgia in 16 PT and 15 PV"
    explanation: >-
      Establishes the 31-patient erythromelalgia denominator used above, rather than the
      50-patient thrombocythemia denominator that would understate the proportion.
- name: Digital ischemic necrosis
  category: Vascular
  description: >-
    Frank ischemic necrosis or gangrene of a toe or fingertip, the end stage of
    unrelieved platelet-mediated acral arteriolar occlusion.
  phenotype_term:
    preferred_term: Digital ischemia
    term:
      id: HP:0033402
      label: Digital ischemia
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Erythromelalgia often progressed to ischemic acrocyanosis or necrosis in toes or fingers."
    explanation: Documents digital ischemic necrosis as an outcome of the untreated occlusive process.
- name: Thrombocytosis
  category: Hematologic
  description: >-
    The underlying haematological abnormality in the myeloproliferative form.
    Erythromelalgia can occur at platelet counts only modestly above the normal
    range, so a markedly raised count is not required to attribute the syndrome to
    the MPN.
  phenotype_term:
    preferred_term: Thrombocytosis
    term:
      id: HP:0001894
      label: Thrombocytosis
  evidence:
  - reference: PMID:8951772
    reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Erythromelalgia in thrombocythemia already occurred at slightly increased platelet counts above 400 x 10(9)/l."
    explanation: Establishes both the presence of thrombocytosis and the low count threshold at which symptoms occur.
biochemical:
- name: Beta-thromboglobulin
  presence: Elevated
  notes: >-
    Alpha-granule release marker of in vivo platelet activation; significantly
    elevated in thrombocythemia patients with erythromelalgia compared with
    asymptomatic thrombocythemia patients and controls, and normalized by aspirin
    in parallel with clinical resolution.
  evidence:
  - reference: PMID:8883266
    reference_title: Erythromelalgia in essential thrombocythemia is characterized by platelet activation and endothelial cell damage but not by thrombin generation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "As compared with asymptomatic ET patients and control subjects erythromelalgia was characterized by significantly higher beta-TG and TM levels but no significant differences were detected in either F1 + 2 or TDP levels."
    explanation: >-
      Beta-thromboglobulin and thrombomodulin are selectively elevated in symptomatic patients while
      thrombin-generation markers are not, marking platelet activation and endothelial injury without coagulation activation.
- name: Thrombomodulin
  presence: Elevated
  notes: >-
    Marker of endothelial cell damage, elevated in symptomatic erythromelalgia and
    falling with aspirin treatment — the biochemical counterpart of the arteriolar
    endothelial injury seen histologically.
  evidence:
  - reference: PMID:8883266
    reference_title: Erythromelalgia in essential thrombocythemia is characterized by platelet activation and endothelial cell damage but not by thrombin generation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment of erythromelalgia with aspirin resulted in disappearance of erythromelalgic signs and symptoms, which was paralleled by a significant decrease of beta-TG and TM levels."
    explanation: Links normalization of the endothelial-damage and platelet-activation markers to clinical remission on aspirin.
- name: Platelet survival time
  presence: Shortened
  notes: >-
    Radiolabelled autologous platelet survival is markedly shortened in
    thrombocythemia complicated by erythromelalgia (4.2 days) relative to
    asymptomatic thrombocythemia (6.6 days) and reactive thrombocytosis (8.0 days),
    and is restored by aspirin — a direct functional readout of ongoing platelet
    consumption in microvascular thrombi.
  evidence:
  - reference: PMID:7792731
    reference_title: 'Platelet consumption in thrombocythemia complicated by erythromelalgia: reversal by aspirin.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean platelet survival time of the erythromelalgia patients was 4.2 +/- 0.2 days, which is significantly decreased as compared with asymptomatic thrombocythemia patients (6.6 +/- 0.3 days, p < 0.001) and patients with reactive thrombocytosis (8.0 +/- 0.4 days, p < 0.001)."
    explanation: Quantifies shortened platelet survival specifically in symptomatic erythromelalgia versus two comparator groups.
  - reference: PMID:7792731
    reference_title: 'Platelet consumption in thrombocythemia complicated by erythromelalgia: reversal by aspirin.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment of erythromelalgia with aspirin increased the mean platelet survival time from 4.0 +/- 0.3 days to 6.9 +/- 0.4 days (p < 0.001)"
    explanation: Aspirin reverses the shortened platelet survival, confirming COX-dependent platelet consumption as the operative process.
- name: Urinary thromboxane B2
  presence: Elevated
  notes: >-
    Stable urinary metabolite of platelet thromboxane A2; increased in
    thrombocythemia patients with erythromelalgia and reduced to normal by aspirin,
    evidencing in vivo thromboxane-dependent platelet activation.
  evidence:
  - reference: PMID:12781799
    reference_title: 'Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a significant reduction of the increased levels of beta-TG, PF4, TM and urinary TxB2 excretion to normal"
    explanation: Aspirin normalizes urinary thromboxane B2 alongside the other platelet-activation markers.
environmental:
- name: Limb warming, exercise, and dependency as attack precipitants
  description: >-
    Erythromelalgic attacks are provoked by warmth and by anything that raises acral
    blood flow or venous pressure — exercise, physical activity, limb dependency,
    prolonged standing, and occlusive footwear — and are relieved by cooling and
    elevation. These are precipitants of the flare, not causes of the underlying
    disorder, so they are modeled as EXACERBATES on the flare node rather than as a
    trigger of the upstream mechanism. Note the therapeutic hazard shared with the
    primary form: patients self-treat by prolonged cold-water immersion, which causes
    skin maceration and secondary tissue injury.
  influences_mechanisms:
  - target: Episodic Acral Burning Pain, Erythema, and Warmth
    environmental_effect: EXACERBATES
    causal_link_type: DIRECT
    description: >-
      Heat and exertion precipitate the erythromelalgic attack; cooling relieves it.
    evidence:
    - reference: PMID:40428878
      reference_title: 'Comparative Efficacy and Tolerability of Treatments for Erythromelalgia: A Systematic Review.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Triggers for symptoms included warmth, exercise, dependency, tight footwear or gloves, physical activity, immersion, and emotional stress."
      explanation: Enumerates the attack precipitants recorded across the systematic review's patient cohorts.
    - reference: PMID:32491719
      reference_title: Erythromelalgia.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "The episodes are typically precipitated by exercise and relieved by cooling the affected parts."
      explanation: States the precipitation-by-exertion and relief-by-cooling pattern that defines the flare.
  evidence:
  - reference: PMID:40428878
    reference_title: 'Comparative Efficacy and Tolerability of Treatments for Erythromelalgia: A Systematic Review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Common relievers involve cooling methods such as local skin cooling or ice water immersion."
    explanation: Documents cooling as the characteristic reliever, the counterpart of the warming trigger.
prevalence:
- population: Olmsted County, Minnesota, USA (population-based, 1976-2005)
  measure_type: ANNUAL_INCIDENCE
  prevalence_class: RARE
  rate_per_100000: 0.2
  rate_low: 0.02
  rate_high: 0.4
  notes: >-
    Population-based age- and sex-adjusted incidence of secondary erythromelalgia
    from the Rochester Epidemiology Project (overall erythromelalgia incidence
    1.3/100,000/yr; primary 1.1/100,000/yr). In this study "secondary" was defined
    by a coexisting myeloproliferative disorder, or attribution to another cause
    such as medications, HIV, or mushroom poisoning. The confidence interval is
    wide and the authors note the small sample size as a limitation.
  evidence:
  - reference: PMID:18713229
    reference_title: 'Incidence of erythromelalgia: a population-based study in Olmsted County, Minnesota.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The incidence of primary and secondary erythromelalgia was 1.1 (0.7-1.5) and 0.2 (0.02-0.4) per 100,000 people per year, respectively."
    explanation: Provides the population-based annual incidence estimate for secondary erythromelalgia.
diagnosis:
- name: Evaluation for an underlying myeloproliferative neoplasm
  description: >-
    Because erythromelalgia is regarded as a pathognomonic microvascular
    complication of essential thrombocythemia and polycythemia vera — and frequently
    its presenting manifestation — a new diagnosis of erythromelalgia warrants
    haematological evaluation for an occult MPN, including a platelet count that may
    be only modestly elevated.
  results: >-
    Thrombocytosis (possibly only slightly above 400 x 10^9/L) with an MPN diagnosis
    supports platelet-mediated secondary erythromelalgia.
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Erythromelalgia was the presenting symptom in 26 of 40 patients with thrombocythemia in its primary form or when associated with polycythemia vera."
    explanation: Erythromelalgia is the presenting symptom in most such patients, justifying MPN evaluation on presentation.
- name: Skin punch biopsy of an affected area
  description: >-
    Histopathology of affected acral skin demonstrates the characteristic arteriolar
    inflammation, fibromuscular intimal proliferation, and platelet-rich thrombotic
    occlusions that distinguish platelet-mediated secondary erythromelalgia from the
    primary neuropathic form.
  results: Arteriolar inflammation, fibromuscular intimal proliferation, and thrombotic occlusion.
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Skin punch biopsy samples taken from the affected areas showed typical arteriolar inflammation, fibromuscular intima proliferation, and thrombotic occlusions."
    explanation: Establishes the diagnostic histopathological findings on skin punch biopsy.
- name: Therapeutic response to aspirin as a diagnostic discriminator
  description: >-
    The dramatic, complete, and sustained response of platelet-mediated
    erythromelalgia to a cyclooxygenase inhibitor is itself diagnostically
    informative: the historical Drenth-Michiels classification of red, burning
    extremities was built on aspirin responsiveness, separating aspirin-responsive
    thrombocythemic erythromelalgia from the aspirin-resistant primary and other
    secondary forms.
  results: Complete relief of pain with aspirin supports the platelet-mediated (MPN-associated) form.
  evidence:
  - reference: PMID:32491719
    reference_title: Erythromelalgia.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The term erythromelalgia and erythermalgia were differentiated on the basis of responsiveness to aspirin by Drenth and Michiels"
    explanation: Documents aspirin responsiveness as the historical basis for discriminating these entities.
treatments:
- name: Low-dose aspirin
  description: >-
    The mechanism-matched treatment of MPN-associated erythromelalgia. Irreversible
    inhibition of platelet cyclooxygenase-1 abolishes the thromboxane-dependent
    platelet activation that drives arteriolar occlusion, producing complete relief
    of pain, restoration of microvascular circulation, normalization of shortened
    platelet survival, and fall of platelet-activation markers to normal. This
    dramatic responsiveness is the therapeutic hallmark separating MPN-associated
    secondary erythromelalgia from the characteristically aspirin-refractory primary
    (SCN9A/Nav1.7) form. Safety caveat: at very high platelet counts
    (roughly >1000-2000 x 10^9/L) thrombocythemia converts to a bleeding diathesis,
    and aspirin — while still preventing the microcirculatory disturbance — further
    increases the risk of serious haemorrhage.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: aspirin
      term:
        id: CHEBI:15365
        label: acetylsalicylic acid
  therapeutic_modality: SMALL_MOLECULE
  target_phenotypes:
  - preferred_term: Erythromelalgia
    term:
      id: HP:0032147
      label: Erythromelalgia
  target_mechanisms:
  - target: Thromboxane-Dependent Platelet Activation and Aggregation
    treatment_effect: INHIBITS
    description: >-
      Aspirin inhibits platelet cyclooxygenase-1, removing the thromboxane metabolites
      shown to be necessary for erythromelalgia to develop and thereby interrupting the
      platelet activation/aggregation node upstream of arteriolar occlusion.
    evidence:
    - reference: PMID:16673274
      reference_title: 'Clinical and laboratory features, pathobiology of platelet-mediated thrombosis and bleeding complications, and the molecular etiology of essential thrombocythemia and polycythemia vera: therapeutic implications.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Inhibition of platelet cyclooxygenase-1 by aspirin is followed by relief of microvascular disturbances"
      explanation: States the drug target (platelet COX-1) and the mechanistic consequence of inhibiting it.
    - reference: PMID:12781799
      reference_title: 'Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Thus, cyclooxygenase metabolites are necessary for erythromelalgia to develop."
      explanation: Establishes that the inhibited pathway is necessary for the disease process, licensing the INHIBITS edge.
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Complete relief of pain and restoration of microvascular circulation disturbances was obtained with the cyclo-oxygenase inhibitors aspirin and indomethacin"
    explanation: Documents complete symptomatic and microvascular response to cyclooxygenase inhibition.
  - reference: PMID:12781799
    reference_title: 'Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Aspirin treatment of erythromelalgia in thrombocythemia patients resulted in the disappearance of the erythromelalgic, thrombotic signs and symptoms, correction of the shortened platelet survival times"
    explanation: Confirms clinical and platelet-kinetic reversal on aspirin.
  - reference: PMID:8951772
    reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this situation aspirin prevents erythromelalgic and microcirculatory circulation disturbances, but further increases the risk of serious bleeding complications."
    explanation: >-
      Support is PARTIAL because it qualifies rather than endorses the treatment — at very high
      platelet counts aspirin remains effective for the microvascular disturbance but raises bleeding risk.
- name: Indomethacin
  description: >-
    A second cyclooxygenase inhibitor with the same mechanism-matched efficacy,
    confirming that the therapeutic effect is a class effect of COX inhibition
    rather than an aspirin-specific property. Notably sodium salicylate and the
    non-COX platelet inhibitors dipyridamole, sulfinpyrazone, ticlopidine, and
    dazoxiben are all ineffective, which is the pharmacological argument for the
    thromboxane mechanism.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: indomethacin
      term:
        id: CHEBI:49662
        label: indometacin
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: Thromboxane-Dependent Platelet Activation and Aggregation
    treatment_effect: INHIBITS
    description: Indomethacin inhibits the same platelet cyclooxygenase pathway targeted by aspirin.
    evidence:
    - reference: PMID:3977194
      reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Complete relief of pain and restoration of microvascular circulation disturbances was obtained with the cyclo-oxygenase inhibitors aspirin and indomethacin, but not with sodium-salicylate or the platelet inhibitors dipyridamole, sulfinpyrazone, ticlopidine, and dazoxiben."
      explanation: >-
        Indomethacin shares aspirin's efficacy while non-COX antiplatelet agents fail, establishing
        cyclooxygenase inhibition as the operative drug mechanism.
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Complete relief of pain and restoration of microvascular circulation disturbances was obtained with the cyclo-oxygenase inhibitors aspirin and indomethacin"
    explanation: Documents complete symptomatic and microvascular relief with indomethacin alongside aspirin.
  - reference: PMID:12781799
    reference_title: 'Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Complete relief from erythromelalgic and acrocyanotic pain is obtained with the cyclooxygenase inhibitors aspirin and indomethacin, but not with sodiumsalicylate, dipyridamol, sulfinpyrozone and ticlopedine."
    explanation: Independently confirms indomethacin efficacy and the failure of non-COX antiplatelet agents.
- name: Cytoreduction of the underlying myeloproliferative neoplasm
  description: >-
    Treating the upstream disorder resolves the erythromelalgia: symptoms remit
    during cytoreduction-induced haematological remission of the thrombocythemia and
    recur on relapse. Contemporary cytoreductive agent selection is a matter for the
    MPN entries (`Polycythemia_Vera`, `Essential_Thrombocythemia`) rather than this
    entry; the historical evidence cited here used busulfan.
  treatment_term:
    preferred_term: cytoreductive therapy
    term:
      id: NCIT:C15632
      label: Chemotherapy
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: Clonal Thrombocythemia in Myeloproliferative Neoplasm
    treatment_effect: INHIBITS
    description: Cytoreduction removes the clonal thrombocythemia that supplies the hyperreactive platelet population.
    evidence:
    - reference: PMID:3977194
      reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The erythromelalgia was alleviated during busulfan-induced remissions of thrombocythemia and its recurrence coincided with relapsing thrombocythemia."
      explanation: Remission of the thrombocythemia relieves the erythromelalgia, supporting an INHIBITS edge on the upstream node.
  evidence:
  - reference: PMID:3977194
    reference_title: Erythromelalgia caused by platelet-mediated arteriolar inflammation and thrombosis in thrombocythemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The erythromelalgia was alleviated during busulfan-induced remissions of thrombocythemia and its recurrence coincided with relapsing thrombocythemia."
    explanation: Cytoreduction-induced haematological remission relieves the erythromelalgia, and relapse brings it back.
  - reference: PMID:12781799
    reference_title: 'Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "which specifically respond to low-dose aspirin or reduction of platelet counts to normal"
    explanation: >-
      Support is PARTIAL — the quoted response applies to the accompanying transient ischemic
      manifestations, but it establishes platelet-count reduction as an effective alternative to aspirin
      for the platelet-mediated microvascular syndrome as a whole.
- name: Treatment of the underlying condition in non-MPN secondary disease
  description: >-
    For acquired erythromelalgia not driven by a myeloproliferative neoplasm,
    management is directed primarily at the underlying disease, supplemented by
    trigger avoidance. Aspirin is characteristically ineffective in these
    non-platelet-mediated forms. Note this is a statement about *cause-directed*
    therapy, not a claim that nothing helps symptomatically — symptomatic options
    with trial evidence are curated in the sibling treatment entry below.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:40428878
    reference_title: 'Comparative Efficacy and Tolerability of Treatments for Erythromelalgia: A Systematic Review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Secondary EM tends to be more variable in presentation, may be unilateral or localized, and treatment usually targets the underlying condition."
    explanation: >-
      A 2025 systematic review states that treatment of secondary erythromelalgia usually targets
      the underlying condition.
  - reference: PMID:29641704
    reference_title: 'Erythromelalgia: a cutaneous manifestation of neuropathy?'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Since there is no specific and effective treatment, control should focus on the underlying disease."
    explanation: >-
      Support is PARTIAL. This 2018 narrative review's blanket "no specific and effective
      treatment" is used only for the cause-directed management principle; the later systematic
      review (PMID:40428878) reports measurable symptomatic benefit for several agents, so the
      unqualified negative is not adopted here.
  - reference: PMID:29641704
    reference_title: 'Erythromelalgia: a cutaneous manifestation of neuropathy?'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The prevention of crisis is based on a strict control of triggers and promotion of preventive measures."
    explanation: Supports trigger control as the preventive component of management.
- name: Symptomatic pharmacotherapy for aspirin-unresponsive disease
  description: >-
    Where the platelet-mediated COX-1 mechanism does not apply — the non-MPN
    acquired routes, and MPN disease inadequately controlled by aspirin — symptomatic
    options with controlled or cohort evidence include topical amitriptyline-ketamine,
    lidocaine, and the prostaglandin analogues iloprost and misoprostol. IMPORTANT
    EVIDENCE CAVEAT, which is why these are curated as a single node without
    per-agent mechanism edges: the systematic review supplying this evidence pooled
    120 patients across primary, idiopathic and secondary erythromelalgia and did NOT
    report outcomes stratified by aetiology, so efficacy specific to secondary
    disease is not established. Misoprostol in particular caused severe
    gastrointestinal toxicity.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: amitriptyline
      term:
        id: CHEBI:2666
        label: amitriptyline
    - preferred_term: ketamine
      term:
        id: CHEBI:6121
        label: ketamine
    - preferred_term: lidocaine
      term:
        id: CHEBI:6456
        label: lidocaine
    - preferred_term: iloprost
      term:
        id: CHEBI:63916
        label: iloprost
    - preferred_term: misoprostol
      term:
        id: CHEBI:63610
        label: misoprostol
  therapeutic_modality: SMALL_MOLECULE
  target_phenotypes:
  - preferred_term: Limb pain
    term:
      id: HP:0009763
      label: Limb pain
  evidence:
  - reference: PMID:40428878
    reference_title: 'Comparative Efficacy and Tolerability of Treatments for Erythromelalgia: A Systematic Review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "About 75% of the patients reported pain relief with topical amitriptyline-ketamine, while lidocaine reduced nociceptive feelings in a dose-dependent manner."
    explanation: >-
      Support is PARTIAL because the pooled cohort mixes primary, idiopathic and secondary
      erythromelalgia and is not stratified by aetiology, so the response rate cannot be
      attributed to secondary disease specifically.
  - reference: PMID:40428878
    reference_title: 'Comparative Efficacy and Tolerability of Treatments for Erythromelalgia: A Systematic Review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Iloprost and misoprostol exhibited notable benefits in cooling scores, sympathetic dysfunction, and EM severity compared to placebos."
    explanation: >-
      Placebo-controlled benefit for the two prostaglandin analogues, again in a mixed-aetiology
      population, hence PARTIAL.
  - reference: PMID:40428878
    reference_title: 'Comparative Efficacy and Tolerability of Treatments for Erythromelalgia: A Systematic Review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "adverse events ranged from mild gastrointestinal symptoms to severe complications such as disability and depression, requiring careful monitoring"
    explanation: Documents the tolerability burden that qualifies these symptomatic options.
- name: Chemical lumbar sympathectomy
  description: >-
    An invasive procedural option for refractory disease, reported to give sustained
    pain reduction with mild thigh pain as the common side effect. Carried as a
    sibling of the symptomatic-pharmacotherapy node under the SAME mixed-aetiology
    caveat: the systematic review supplying this evidence pooled 120 patients across
    primary, idiopathic and secondary erythromelalgia (13 of them receiving CLS) and
    did not stratify outcomes by aetiology, so efficacy in secondary disease is not
    established. Long-term outcomes are additionally underreported, and relapse is
    described in patients carrying SCN9A variants — a caveat belonging to the primary
    form, noted here only because it is inseparable from the pooled cohort. Term
    note: NCIT has no verifiable term for sympathectomy specifically, so the generic
    verified action term is used with a precise `preferred_term`; the procedure is a
    percutaneous chemical neurolysis rather than open surgery, though `SURGERY` is
    the closest available `therapeutic_modality` bucket for an invasive procedure.
  treatment_term:
    preferred_term: chemical lumbar sympathectomy
    term:
      id: NCIT:C49236
      label: Therapeutic Procedure
  therapeutic_modality: SURGERY
  target_phenotypes:
  - preferred_term: Limb pain
    term:
      id: HP:0009763
      label: Limb pain
  evidence:
  - reference: PMID:40428878
    reference_title: 'Comparative Efficacy and Tolerability of Treatments for Erythromelalgia: A Systematic Review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "observed significant pain reduction with CLS, with mild thigh pain as a side effect."
    explanation: >-
      Support is PARTIAL — significant pain reduction is reported, but within a mixed-aetiology
      pooled review that does not separate secondary from primary/idiopathic disease.
  - reference: PMID:40428878
    reference_title: 'Comparative Efficacy and Tolerability of Treatments for Erythromelalgia: A Systematic Review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Despite encouraging short-term results, long-term outcomes after CLS remain underreported and variable."
    explanation: >-
      Qualifies the procedure: encouraging short-term results but underreported and variable
      long-term outcomes, which is why this is curated as an option rather than a recommendation.
differential_diagnoses:
- name: Primary erythermalgia
  disease_term:
    preferred_term: primary erythermalgia
    term:
      id: MONDO:0007571
      label: primary erythermalgia
  description: >-
    The principal differential. Primary/inherited erythromelalgia is an autosomal
    dominant SCN9A (Nav1.7) gain-of-function channelopathy of nociceptors,
    characteristically bilateral and symmetric, and characteristically refractory to
    aspirin — the mechanistic and therapeutic mirror image of the platelet-mediated
    secondary form modeled here. Curated separately as `Primary_Erythermalgia`.
  evidence:
  - reference: PMID:8203771
    reference_title: 'Thrombocythemic erythromelalgia, primary erythermalgia, and secondary erythermalgia: three distinct clinicopathologic entities.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the authors discern three distinct types of red, congested, and burning extremities that need to be distinguished for effective treatment according to their etiology: erythromelalgia in thrombocythemia, primary erythermalgia, and secondary erythermalgia"
    explanation: >-
      Establishes that thrombocythemic erythromelalgia and primary erythermalgia are distinct
      clinicopathologic entities requiring different treatment.
  - reference: PMID:32491719
    reference_title: Erythromelalgia.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Primary erythermalgia: Refers to an idiopathic or inherited disorder. Also called aspirin-resistant erythermalgia of unknown origin."
    explanation: Documents the aspirin resistance of primary erythermalgia, the therapeutic discriminator from the MPN-associated form.
  - reference: PMID:30609105
    reference_title: Review of primary and secondary erythromelalgia.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "recent discoveries of the genetic mutations that now define primary erythromelalgia, as opposed to secondary erythromelalgia"
    explanation: States that genetic mutations define the primary form in contradistinction to the secondary form.
- name: Superficial thrombophlebitis
  description: >-
    Painful red, warm, indurated erythromelalgic "hot spots" on the skin of the
    upper legs in thrombocythemia are readily misdiagnosed as superficial
    thrombophlebitis, which would be treated quite differently.
  evidence:
  - reference: PMID:8951772
    reference_title: 'Erythromelalgic, thrombotic and hemorrhagic manifestations in 50 cases of thrombocythemia.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Painful red, warm and indurated erythromelalgic hot spots in the skin of the upper legs were misdiagnosed as superficial thrombophelebitis in 5 PT and 2 PV patients."
    explanation: Documents this specific misdiagnosis in 7 of 50 thrombocythemia patients.
discussions:
- discussion_id: av_shunting_vs_occlusion_paradox
  prompt: >-
    How does an arteriole occluded by platelet-rich thrombi produce a skin surface that
    is visibly red and *hotter* than normal? Is microvascular arteriovenous shunting
    the reconciling mechanism, and if so does it operate in the MPN-associated form or
    only in the non-platelet acquired routes?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Episodic Acral Burning Pain, Erythema, and Warmth
  - pathophysiology#Acral Arteriolar Microvascular Occlusion
  rationale: >-
    This entry's occlusive model has an unresolved surface paradox. The demonstrated
    lesion is arteriolar obstruction by platelet-rich thrombi, which should reduce
    perfusion — yet the defining clinical sign is a red, warm, congested extremity,
    and the flare node above therefore deliberately binds no `vasodilation` process
    rather than assert a mechanism it cannot evidence.


    The classical reconciliation is microvascular arteriovenous shunting: blood
    bypasses the nutritive capillary bed through shunts, so the skin is simultaneously
    hyperemic and warm at the surface while the tissue itself is hypoxic. That model
    is asserted in the older review literature (PMID:15075045) but, critically, is
    asserted there as a *single common mechanism for all* erythromelalgia — a claim
    the later Nav1.7 channelopathy findings contradict, and which this KB already
    flags as PARTIAL on the umbrella `erythromelalgia` entry. The deep-research report
    for this entry describes the same shunting model with a low-transcutaneous-oxygen
    correlate, but its only source there is a textbook chapter with no PMID and no
    quotable passage, so it cannot be curated as an evidence-backed pathophysiology
    node.


    What would settle it: paired measurements in *aetiologically stratified* patients
    — laser Doppler skin blood flow and transcutaneous oxygen tension during a flare,
    in MPN-associated versus non-MPN secondary disease. Until then this entry models
    only what the histopathology and platelet kinetics directly demonstrate, and
    records the shunting hypothesis here rather than promoting it to a node.
  evidence:
  - reference: PMID:15075045
    reference_title: Erythromelalgia.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "A wide variety of etiological conditions can cause erythromelalgia, all having a single common pathogenetic mechanism - microvascular arteriovenous shunting."
    explanation: >-
      States the arteriovenous-shunting hypothesis. Support is PARTIAL and deliberately so: this
      2004 review asserts shunting as the SINGLE common mechanism across all erythromelalgia,
      which the SCN9A/Nav1.7 findings curated in `Primary_Erythermalgia` contradict. It is cited
      as the source of an open hypothesis, not as support for a curated mechanism.
  - reference: PMID:8883266
    reference_title: Erythromelalgia in essential thrombocythemia is characterized by platelet activation and endothelial cell damage but not by thrombin generation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "intravascular activation and aggregation of platelets with subsequent sludging or occlusion of the acral arterial microvasculature"
    explanation: >-
      Establishes the occlusive half of the paradox — the demonstrated lesion in MPN-associated
      disease is microvascular occlusion, which is what makes the warm, hyperemic surface
      appearance require an explanation.
- discussion_id: secondary_em_nomenclature_scope
  prompt: >-
    Does MONDO:0035149 "secondary erythromelalgia" include the platelet-mediated
    erythromelalgia of the myeloproliferative neoplasms, or only the
    aspirin-resistant non-MPN acquired forms that the historical Drenth-Michiels
    classification called "secondary erythermalgia"?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Clonal Thrombocythemia in Myeloproliferative Neoplasm
  - pathophysiology#Non-Platelet Acquired Routes (Neuropathic, Autoimmune, Drug-Induced)
  rationale: >-
    Two incompatible nomenclatures are in circulation. The historical
    Drenth-Michiels scheme is three-way and defined by aspirin responsiveness:
    (a) aspirin-responsive erythromelalgia in thrombocythemia, (b) aspirin-resistant
    primary erythermalgia, (c) aspirin-resistant "secondary erythermalgia" associated
    with other medical conditions. Under that scheme, MPN-associated disease is NOT
    "secondary". Contemporary usage is instead a two-way primary/secondary split that
    places MPN-associated disease squarely within "secondary" — the Olmsted County
    population study classified patients as secondary precisely when they had a
    coexisting myeloproliferative disorder, and a 2025 systematic review lists
    myeloproliferative disorders first among the conditions secondary EM is linked to.
    This entry follows that contemporary usage and models the MPN platelet arm as the
    principal, best-evidenced secondary mechanism, while retaining the non-MPN routes
    as a separate, deliberately low-resolution node.


    THE GAP, stated precisely: which of the two senses MONDO:0035149 itself intends is
    NOT established here. Its only synonym is "Secondary erythermalgia" EXACT
    [Orphanet:529864] — i.e. Orphanet's label is the very term the historical narrow
    scheme used for the aspirin-RESISTANT non-MPN category. No Orphanet definition row
    was quotable at curation time (the Orphadata bulk XML was not available locally),
    so this entry's scope decision rests on contemporary clinical/epidemiological usage
    rather than on a cited ontology definition. Resolving it needs
    `just structured-rebuild-orphanet --id 529864` and a quoted `ORPHA:529864`
    definition row. Curators reading the older literature should meanwhile note that
    "secondary erythermalgia" there means something narrower than this entry's scope,
    and that the aspirin-responsiveness contrast is therefore a contrast between the
    MPN arm and everything else, not between "secondary" and "primary" as such.
  evidence:
  - reference: PMID:32491719
    reference_title: Erythromelalgia.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "(a) Erythromelalgia in thrombocythemia: It is platelet mediated and aspirin responsive. This occurs in association with essential thrombocytosis and polycythemia vera."
    explanation: >-
      Documents the historical three-way classification in which thrombocythemic erythromelalgia is
      its own aspirin-responsive category, separate from "secondary erythermalgia".
  - reference: PMID:18713229
    reference_title: 'Incidence of erythromelalgia: a population-based study in Olmsted County, Minnesota.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients were considered to have secondary erythromelalgia if they had a coexisting diagnosis of a myeloproliferative disorder such as polycythemia vera, chronic myelocytic leukemia, or thrombocythemia at the time of diagnosis of erythromelalgia"
    explanation: >-
      Contemporary epidemiology classifies MPN-associated disease as secondary, the usage this
      entry follows and the one matching MONDO/Orphanet.
clinical_trials: []
datasets: []
📚

References & Deep Research

Deep Research

1
Falcon ▸
Secondary Erythromelalgia: Disease-Characteristics Research Report
Edison Scientific Literature 16 citations 2026-08-17T09:14:00.381835

Secondary Erythromelalgia: Disease-Characteristics Research Report

Executive summary and evidence caveat

Secondary erythromelalgia (secondary EM) is an acquired, etiologically heterogeneous neurovascular pain syndrome characterized by recurrent or persistent burning pain, erythema, and increased skin temperature, usually in the feet or hands. Heat, exercise, dependency of the limb, prolonged standing, and tight footwear provoke attacks; cooling and elevation typically relieve them. Unlike inherited primary erythromelalgia, secondary EM is not itself an established monogenic channelopathy. It usually appears later in life in association with a myeloproliferative neoplasm (MPN), small-fiber or autonomic neuropathy, autoimmune/connective-tissue disease, metabolic disease, medication, infection, malignancy, toxin, or tissue injury. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 2-3, algarni2025comparativeefficacyand pages 1-2)

The major evidence limitation is that most cohorts and therapeutic studies combine primary, idiopathic, and secondary EM. Consequently, many frequency and response estimates below describe EM overall, not secondary EM specifically. Secondary-disease evidence is strongest for the association between platelet-mediated MPNs and aspirin-responsive EM; most other associations and treatments rely on small observational studies, case series, or expert reviews. (skeik2019erythromelalgia pages 1-2, algarni2025comparativeefficacyand pages 4-5, algarni2025comparativeefficacyand pages 1-2)

Domain Key finding Evidence type/strength Knowledge-base annotation
Definition / phenotype Secondary erythromelalgia is an acquired neurovascular pain syndrome defined by episodic or persistent burning pain, erythema, warmth, and sometimes swelling, usually in distal extremities; attacks are precipitated by heat, exercise, dependency, footwear, and relieved by cooling/elevation. Compared with inherited primary disease, secondary disease tends to present later and may be more variable, unilateral, or localized. Quantitative phenotype data usually pool primary and secondary cases. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 2-3, algarni2025comparativeefficacyand pages 1-2, algarni2025comparativeefficacyand pages 4-5) Expert review + systematic review; moderate for core phenotype, lower for subtype distinctions HPO: Erythema, Burning pain, Increased skin temperature, Distal extremity pain, Edema; UBERON: foot, hand, lower limb; MONDO: secondary erythromelalgia if available/not confirmed
Major secondary causes Reported associations include myeloproliferative neoplasms/disorders (especially essential thrombocythemia, polycythemia vera, myelodysplastic syndromes), neuropathies/small-fiber neuropathy, autoimmune/connective-tissue disease, diabetes/metabolic disease, neoplasia, infections/vaccination, and drugs/toxins such as cyclosporine, calcium-channel blockers, bromocriptine, mercury, burns/frostbite, and mushroom intoxication. Much of this evidence is case-based or mixed-etiology review evidence. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 1-2, algarni2025comparativeefficacyand pages 1-2, algarni2025comparativeefficacyand pages 4-5) Review-level evidence with many case associations; heterogeneous/variable strength Disease associations: MPN, SFN, autoimmune disease, diabetes mellitus, neoplasm, infection, drug-induced disease, toxic exposure
Mechanism / pathophysiology Secondary erythromelalgia is mechanistically heterogeneous. In hematologic forms, platelet activation/microthrombotic or prostaglandin-thromboxane-related microvascular dysfunction is the classic model; in neuropathic forms, small-fiber/autonomic dysfunction and vasomotor dysregulation are implicated. Reviews also support abnormal autonomic testing, reduced nerve terminal density, increased skin blood flow/temperature, and tissue hypoxia/shunting concepts, but these mechanisms are often inferred from mixed erythromelalgia cohorts rather than secondary-only cohorts. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 1-2, skeik2019erythromelalgia pages 2-3) Mixed human clinical + expert review; moderate for MPN/aspirin-responsive mechanism, lower for unified mechanism GO: platelet activation, blood coagulation, regulation of vasodilation, sensory perception of pain, axon guidance/maintenance, autonomic nervous system process; CL: platelet, peripheral sensory neuron, sympathetic neuron, endothelial cell
Diagnostics Diagnosis is primarily clinical: characteristic attacks of red-hot painful extremities triggered by warmth and relieved by cooling, plus exclusion of mimics and search for an underlying cause. Ancillary tests that may support or subtype disease include CBC/platelets and MPN evaluation, vascular studies (often normal large-vessel Doppler but increased skin temperature/laser Doppler and low TcPO2), autonomic testing, thermography, and skin biopsy for nerve fiber density or intraluminal thrombi. Differential diagnoses include peripheral neuropathy, CRPS, cellulitis/erysipelas, dermatitis, osteomyelitis, SLE, venous/arterial insufficiency, and gout. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 2-3) Clinical review evidence; moderate for workup principles, limited formal criteria HPO/differential tags; labs: CBC, platelet count; procedures: skin biopsy, autonomic reflex screen, thermography, laser Doppler, transcutaneous oxygen pressure
Epidemiology Secondary-specific epidemiology is poorly defined. Mixed erythromelalgia estimates cited in reviews include incidence of 1.3/100,000 in Olmsted County and 15/100,000 in New Zealand; reported presentation age ranges 5-90 years with mean around 55 years and female predominance in mixed/reviewed cohorts. An anatomic series cited in review found 88.1% foot involvement, 25.6% hands, 13.7% legs, 2.4% face. These statistics generally do not isolate secondary disease. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 2-3, algarni2025comparativeefficacyand pages 1-2) Mostly retrospective/review data; weak-to-moderate for secondary disease specifically Epidemiology note: mixed EM data; Age of onset: adult/later onset enrichment in secondary EM; Sex: female predominance reported
Treatment First-line management is cause-directed plus trigger avoidance and safe cooling. Aspirin is particularly relevant in myeloproliferative-associated secondary erythromelalgia and is a classic response marker in platelet-mediated disease. Other options reported across mixed cohorts include topical amitriptyline-ketamine, lidocaine, misoprostol, iloprost, antihistamines, venlafaxine/SNRI-class drugs, sodium-channel blockers, and procedural escalation (e.g., sympathectomy, neuromodulation) for refractory cases. Systematic-review data across mixed EM showed ~75% pain relief with topical amitriptyline-ketamine and GI toxicity with misoprostol; applicability to secondary EM is uncertain. (skeik2019erythromelalgia pages 1-2, skeik2019erythromelalgia pages 2-3, algarni2025comparativeefficacyand pages 6-7, algarni2025comparativeefficacyand pages 7-9, algarni2025comparativeefficacyand pages 2-4) Strongest for aspirin in MPN-associated disease from longstanding clinical experience/review; otherwise mostly small mixed studies NCIT/CHEBI: Aspirin, Amitriptyline, Ketamine, Lidocaine, Misoprostol, Iloprost, Venlafaxine; care pathway: treat underlying cause + symptomatic pain management
Trials / recent developments Recent interventional trials mostly target primary/inherited or idiopathic erythromelalgia, not secondary disease. Examples: EASE/ATX01 topical amitriptyline Phase 2 crossover completed 2024 (14 participants), but exclusion criteria removed patients with other extremity pain causes; burst spinal cord stimulation trial enrolls only primary/idiopathic disease; earlier XPF-001/XPF-002 and PF-05089771 trials were for primary/inherited disease. Thus, current trial evidence is not directly generalizable to secondary erythromelalgia. (NCT04039633 chunk 1, NCT05917912 chunk 1, NCT05917912 chunk 2, NCT01090622 chunk 1, NCT01486446 chunk 2, NCT01769274 chunk 3) High confidence for exclusion/generalizability statement from trial records ClinicalTrials: NCT05917912, NCT04039633, NCT01090622, NCT01486446, NCT01769274; intervention classes: topical analgesic, spinal cord stimulation, Nav1.7-targeted agents
Genetics / molecular SCN9A and Nav1.7 are central to inherited primary erythromelalgia, not to secondary erythromelalgia. No established secondary-EM-specific germline causal gene, protective allele, modifier gene, epigenetic signature, or structural chromosomal abnormality was identified in the reviewed evidence. In secondary disease, molecular findings may instead derive from the underlying associated disorder (e.g., somatic driver mutations of myeloproliferative neoplasms), rather than erythromelalgia itself. (assaad2025severeerythromelalgiapain pages 6-8, algarni2025comparativeefficacyand pages 1-2) High confidence for SCN9A-primary distinction; low evidence for secondary-EM-specific genetics because evidence is largely absent HGNC/OMIM note: SCN9A relevant mainly to inherited primary EM; secondary EM genetics: none established at disease level
Models Available experimental systems predominantly model inherited primary erythromelalgia, including iPSC-derived sensory neurons carrying SCN9A variants and Nav1.7-related preclinical pain models. These are useful for nociceptor hyperexcitability and analgesic discovery but do not faithfully model the heterogeneous acquired mechanisms of secondary erythromelalgia. No validated natural animal disease or dedicated acquired secondary-EM model was identified in the available evidence. (NCT01769274 chunk 3) Indirect/model evidence; low for secondary disease relevance Model annotation: human iPSC sensory neuron model for primary EM; secondary EM model status: none established

Table: This table summarizes evidence-grade findings for secondary erythromelalgia across clinical, mechanistic, diagnostic, epidemiologic, therapeutic, genetic, and model domains. It highlights where evidence is strong, where data are mixed with primary erythromelalgia, and where disease-specific gaps remain.

1. Disease information

Definition and classification

The name derives from Greek erythros (red), melos (limb), and algos (pain). Common names are erythromelalgia, erythermalgia, erythralgia, Mitchell disease, and, when acquired, secondary erythromelalgia/secondary erythermalgia. The syndrome’s defining clinical triad is red, hot, painful extremities. Swelling may accompany attacks. Secondary EM is best represented as a disease-level syndrome, aggregated from clinical literature and disease resources—not as an individual-patient/EHR datum unless a knowledge-base record explicitly links it to a patient. (skeik2019erythromelalgia pages 1-2, skeik2019erythromelalgia pages 2-3)

Identifiers

  • ICD-10-CM: I73.81, Erythromelalgia. This code does not reliably distinguish primary from secondary disease.
  • MeSH: Erythromelalgia; a separate secondary-EM descriptor is generally not used.
  • MONDO: A dedicated, independently curated secondary-EM MONDO identifier could not be confirmed from the retrieved evidence. Use the parent erythromelalgia concept plus a “secondary/acquired” qualifier and causal-disease relationship rather than assigning an unverified ID.
  • OMIM: OMIM entries chiefly describe inherited primary erythromelalgia associated with SCN9A; these should not be used as identifiers for acquired secondary EM.
  • Orphanet/ICD-11: Erythromelalgia concepts may be indexed, but a separate secondary-disease identifier was not verified in the available evidence.

2. Etiology, risks, protective factors, and gene–environment interaction

Causal or associated factors

  1. Hematologic/MPN: essential thrombocythemia, polycythemia vera, myelodysplastic syndromes, and related platelet disorders. These are the most clinically actionable secondary causes. Platelet activation, aggregation, and arteriolar microthrombosis are implicated.
  2. Neuropathic/metabolic: small-fiber neuropathy, diabetic neuropathy/diabetes mellitus, and other peripheral or autonomic neuropathies.
  3. Autoimmune/connective-tissue: systemic lupus erythematosus and other connective-tissue or inflammatory disorders.
  4. Neoplastic/paraneoplastic: solid tumors, hematologic malignancy, and paraproteinemic states have been reported.
  5. Drug-associated: calcium-channel blockers, bromocriptine, and cyclosporine are repeatedly listed; individual drug associations generally derive from case reports.
  6. Infectious or immune triggers: HIV, infectious mononucleosis, and temporal associations with influenza or hepatitis-B vaccination have been reported, but causality is weak.
  7. Toxic/physical injury: mercury exposure, mushroom intoxication, burns, and frostbite are reported associations. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 1-2, algarni2025comparativeefficacyand pages 4-5)

Risk and protective factors

Older age and the presence of an underlying MPN, neuropathy, diabetes, autoimmune disease, malignancy, or an implicated medication increase clinical suspicion. Heat exposure, exercise, prolonged standing, limb dependency, emotional stress, and occlusive footwear are attack triggers, not necessarily causes of the underlying disease. Female predominance has been reported in mixed EM cohorts, but a secondary-specific sex ratio is unavailable. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 2-3, algarni2025comparativeefficacyand pages 4-5)

No validated genetic protective variant, dietary factor, medication prophylaxis, or population-level environmental protective exposure has been established. Avoidance of heat and mechanical triggers reduces attacks but should be classified as symptom prevention rather than protection against disease onset.

Gene–environment interaction

No reproducible secondary-EM-specific gene–environment interaction is established. Genetic or somatic drivers may belong to the underlying disorder—for example, MPN biology—while heat or dependency precipitates symptoms through altered microvascular and neural control. This differs fundamentally from inherited EM, in which a germline channel variant directly changes nociceptor excitability.

3. Phenotypes

Phenotype Type and characteristics Suggested HPO annotation
Burning distal-extremity pain Cardinal subjective symptom; episodic or continuous; mild to incapacitating; attacks last minutes to days Burning pain; Pain in extremities; Foot pain; Hand pain
Erythema Cardinal visible sign; attack-related, localized, unilateral, asymmetric, or bilateral Erythema
Increased skin temperature Cardinal sign; worsened by warmth/exercise/dependency Increased skin temperature
Swelling Variable accompanying manifestation Peripheral edema
Heat intolerance/heat-triggered attacks Provocation phenotype Heat intolerance
Dysesthesia, allodynia, hyperalgesia Especially when small-fiber neuropathy is present Dysesthesia; Allodynia; Hyperalgesia
Abnormal sweating/autonomic findings Variable; supports small-fiber/autonomic involvement Abnormality of the autonomic nervous system; Abnormal sweating
Ulceration, infection, ischemic injury Usually secondary to severe disease or excessive cooling Skin ulcer; Recurrent skin infections; Peripheral ischemia

Secondary EM generally has adult or late onset, although onset across all EM forms ranges from childhood to old age. It may be unilateral or localized more often than inherited primary EM, and its course follows the causal disorder: episodic, fluctuating, progressive, or treatment-responsive. Reviews report ages of 5–90 years, with a mean around 55 years, but this is not a secondary-only estimate. (assaad2025severeerythromelalgiapain pages 6-8, algarni2025comparativeefficacyand pages 1-2)

In a 168-patient mixed EM series cited by a systematic review, involvement was reported in the feet in 88.1%, hands in 25.6%, legs in 13.7%, and face in 2.4%. Approximately 5% reported family history, further illustrating that most EM is not clearly familial, although these values do not isolate secondary cases. (algarni2025comparativeefficacyand pages 1-2)

Quality of life

Severe attacks interfere with walking, standing, sleep, footwear, work, schooling, and social participation. Patients may resort to continuous cooling or water immersion, creating secondary wounds and infection. Disability, depression, and substantial pain interference are recognized, but validated secondary-EM-specific EQ-5D, SF-36, or PROMIS population norms are unavailable. Modern trials use EQ-5D-5L, Brief Pain Inventory, depression scores, physical activity, and disability measures, reflecting the syndrome’s multidimensional burden. (NCT04039633 chunk 1, NCT05917912 chunk 1)

4. Genetic and molecular information

Distinction from primary erythromelalgia

SCN9A encodes the voltage-gated sodium channel NaV1.7. Germline gain-of-function variants cause inherited primary EM by lowering nociceptor firing thresholds. That mechanism should not be automatically attributed to secondary EM. Genetic testing is appropriate when onset is early, disease is familial, or the phenotype suggests a channelopathy; it is not a confirmatory test for acquired secondary EM. Reviews report SCN9A variants in 5–36% of selected EM cohorts, but those mixed and referral-enriched estimates do not establish genetic causation in secondary disease. (skeik2019erythromelalgia pages 2-3, algarni2025comparativeefficacyand pages 6-7, algarni2025comparativeefficacyand pages 1-2)

No secondary-EM-specific germline causal gene, HGNC-listed modifier, protective allele, recurrent pathogenic copy-number change, chromosomal abnormality, or validated ACMG variant set is established. Therefore, secondary EM has no meaningful disease-level carrier frequency, penetrance, anticipation, founder effect, or consanguinity pattern.

Where secondary EM accompanies an MPN, somatic molecular findings such as an MPN driver belong to the underlying neoplasm, not to EM as an independent inherited disorder. Likewise, no reproducible secondary-EM-specific methylation, histone, transcriptomic, proteomic, metabolomic, lipidomic, single-cell, spatial-transcriptomic, or multi-omic signature was identified.

5. Environmental, lifestyle, and infectious information

Ambient heat, heated bedding, exercise, prolonged standing, limb dependency, physical activity, emotional stress, and tight shoes commonly precipitate symptoms. Cooling and elevation reduce them. These relationships represent thermoregulatory and hemodynamic provocation rather than traditional epidemiologic exposures. (skeik2019erythromelalgia pages 2-3, algarni2025comparativeefficacyand pages 4-5)

Mercury toxicity, mushroom intoxication, burns, and frostbite are reported potential causes; calcium-channel blockers, bromocriptine, and cyclosporine are medication associations. HIV and infectious mononucleosis have been reported, while vaccine associations are low-level temporal evidence and should not be treated as established causality. Smoking, alcohol intake, diet, obesity, radiation, and occupational exposure have no validated secondary-EM-specific risk estimates in the retrieved literature. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 1-2)

6. Mechanism and pathophysiology

Secondary EM is probably a final common phenotype produced by several upstream mechanisms.

A. Platelet–microvascular pathway

Underlying MPN/platelet activation → platelet aggregation and prostanoid/thromboxane signaling → arteriolar inflammation or microthrombosis → maldistributed skin perfusion and tissue hypoxia → reactive hyperemia, warmth, erythema, and ischemic burning pain. Clinical aspirin responsiveness supports this model, particularly in essential thrombocythemia or polycythemia vera. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 2-3)

Suggested annotations: - GO biological processes: platelet activation; platelet aggregation; blood coagulation; regulation of vasodilation; inflammatory response; response to hypoxia. - Cell Ontology: platelet; endothelial cell; vascular smooth-muscle cell. - Anatomical: cutaneous arteriole; dermal microvasculature.

B. Neuropathic/autonomic pathway

Diabetes, autoimmune neuropathy, toxic injury, or idiopathic small-fiber damage → dysfunction/loss of nociceptive and autonomic fibers → abnormal thermal pain signaling plus impaired sympathetic vasoconstriction and sweating → episodic vasodilation, heat, erythema, allodynia, and burning pain. Reduced nerve-terminal density and abnormal autonomic reflex testing support this pathway, although studies often combine EM subtypes. (skeik2019erythromelalgia pages 1-2, skeik2019erythromelalgia pages 2-3)

Suggested annotations: - GO: sensory perception of pain; detection of temperature stimulus; regulation of blood vessel diameter; autonomic nervous system process; axon maintenance. - CL: peripheral sensory neuron; nociceptor; sympathetic neuron; Schwann cell; endothelial cell.

C. Arteriovenous shunting and hypoxia

Thermoregulatory dyscontrol may open arteriovenous shunts while reducing nutritive capillary flow. This can produce the paradox of a visibly hyperemic, warm extremity with low transcutaneous oxygen tension and ischemic pain. Large-vessel Doppler studies may remain normal while skin temperature and laser-Doppler flow increase. (skeik2019erythromelalgia pages 2-3)

No single molecular pathway—MAPK, mTOR, PI3K–AKT, Wnt, or otherwise—has been validated as a unifying secondary-EM pathway. Mitochondrial, metabolic, and immune abnormalities should be annotated according to the underlying disease rather than inferred for all secondary EM.

7. Anatomical structures affected

  • Organ/system level: skin and cutaneous circulation; peripheral and autonomic nervous systems; hematologic system when an MPN is causal.
  • Primary sites: feet and toes most commonly, followed by hands/fingers and legs; face and ears are uncommon.
  • Tissues: epidermis and dermis, cutaneous sensory/autonomic nerve fibers, arterioles, venules, capillaries, and arteriovenous anastomoses.
  • Cells: nociceptors, sympathetic neurons, endothelial cells, vascular smooth-muscle cells, and—within MPN-associated disease—platelets.
  • Subcellular: plasma membrane ion channels and synaptic/axonal compartments are relevant to neural excitability, but NaV1.7 dysfunction is proven mainly in inherited disease.
  • Localization/lateralization: bilateral and symmetric disease is typical overall, but acquired disease may be unilateral, asymmetric, or localized. (algarni2025comparativeefficacyand pages 1-2)

Suggested UBERON concepts include skin of foot, foot, toe, hand, finger, lower limb, upper limb, dermis, epidermis, peripheral nerve, blood vessel, and cutaneous microvasculature.

8. Temporal development

Secondary EM usually begins after or around the onset of its associated disease and is commonly adult-onset. Presentation may be acute after a drug or injury, subacute with inflammatory disease, or insidious with MPN or neuropathy. Attacks last minutes to days, may increase during summer, and range from intermittent flares to continuous symptoms. No validated stage system exists. (skeik2019erythromelalgia pages 2-3)

Remission may follow withdrawal of an offending drug or successful treatment of the underlying disease. MPN-associated symptoms can respond rapidly to antiplatelet and cytoreductive treatment. Neuropathy-associated disease is often chronic and variably treatment-responsive. There is no established critical developmental window, although early recognition is important to prevent cooling injury and to detect an occult hematologic disorder.

9. Inheritance, epidemiology, and population

Secondary EM is acquired/non-Mendelian. Inheritance, penetrance, carrier frequency, anticipation, germline mosaicism, and prenatal recurrence risk are not applicable unless testing instead establishes inherited primary EM.

Population incidence is poorly defined. Mixed EM studies cited in reviews reported approximately 1.3 per 100,000 person-years in Olmsted County and 15 per 100,000 in New Zealand, with female predominance. Geographic differences may reflect case definition and ascertainment rather than true biology. Secondary-specific prevalence, incidence, ethnic distribution, and male:female ratio remain unknown. (skeik2019erythromelalgia pages 2-3)

10. Diagnostics

Clinical diagnosis

Diagnosis is based on the characteristic triad and provocation pattern. A photograph taken during an attack can be useful when the examination is normal between flares. There are no universally accepted validated diagnostic criteria or disease-specific biomarker. The source wording that diagnosis is “usually clinical” accurately summarizes current practice. (skeik2019erythromelalgia pages 1-2)

Cause-directed workup

  1. CBC with differential and serial platelet/hematocrit assessment; evaluate persistent thrombocytosis or erythrocytosis for MPN.
  2. Metabolic/neuropathy evaluation: fasting glucose or HbA1c, vitamin B12, thyroid studies, renal/hepatic testing, serum protein electrophoresis/immunofixation as clinically indicated.
  3. Autoimmune/inflammatory testing: ANA and disease-specific serologies only when history or examination supports them.
  4. Medication, infection, toxin, and injury history.
  5. Vascular studies: pulses and ankle-brachial index/Doppler to exclude occlusive disease; large-vessel Doppler may be normal in EM.
  6. Small-fiber/autonomic tests: quantitative sensory testing, autonomic reflex screen, sudomotor tests, and 3-mm skin biopsy for intraepidermal nerve-fiber density when neuropathy is suspected.
  7. Thermography/laser Doppler/TcPO2: supportive research or specialist tests, not standalone diagnostic standards. Skin biopsy may show reduced nerve density or intraluminal thrombi but is neither necessary nor specific. (assaad2025severeerythromelalgiapain pages 6-8, skeik2019erythromelalgia pages 2-3)

Genetic testing

Single-gene SCN9A testing or a pain-channel/small-fiber-neuropathy panel is reasonable for childhood onset, a family history, or a strongly inherited phenotype. WES/WGS may be considered after specialist assessment when a monogenic disorder remains likely. CMA, karyotyping, FISH, mitochondrial DNA testing, and repeat-expansion testing have no routine role in secondary EM. There is no role for population, newborn, or carrier screening.

Differential diagnosis

Important alternatives are complex regional pain syndrome, Raynaud phenomenon/reperfusion, cellulitis or erysipelas, contact dermatitis, vasculitis, gout, osteomyelitis, arterial or venous insufficiency, acrocyanosis, Fabry disease, peripheral neuropathy, small-fiber neuropathy without EM, and systemic lupus erythematosus. CRPS is often unilateral and follows trauma with trophic/sudomotor abnormalities; cellulitis is persistent and infectious rather than heat-provoked and rapidly cooling-responsive. (skeik2019erythromelalgia pages 2-3)

11. Outcomes and prognosis

Secondary EM itself has no established disease-specific mortality rate, survival curve, or reduction in life expectancy. Prognosis depends mainly on the underlying disorder and severity of pain. MPN-associated cases may improve substantially with antiplatelet and disease-directed therapy; acquired neuropathic cases may remain chronic.

Morbidity can be profound: impaired walking, sleep loss, inability to tolerate shoes or warm environments, work/school limitation, anxiety, depression, and social isolation. Complications include maceration, ulceration, infection, tissue ischemia, and rarely amputation—often worsened by prolonged ice or water exposure. (skeik2019erythromelalgia pages 2-3, algarni2025comparativeefficacyand pages 1-2)

Favorable prognostic features include identification of a reversible cause and aspirin-responsive MPN disease. Persistent severe pain, established neuropathy, ulceration, and delayed cause recognition predict greater morbidity. No validated molecular prognostic biomarker exists.

12. Treatment and current applications

Treatment strategy

  1. Identify and treat the underlying cause.
  2. Avoid attacks safely: cool environment, fans, elevation, breathable footwear, activity pacing; avoid direct ice and prolonged immersion.
  3. MPN-associated disease: low-dose aspirin when not contraindicated; manage the MPN with hematology-directed phlebotomy or cytoreduction as appropriate.
  4. Localized symptoms: topical lidocaine or compounded amitriptyline–ketamine.
  5. Neuropathic phenotype: gabapentinoids, SNRIs, tricyclics, or sodium-channel blockers selected according to comorbidity and safety.
  6. Refractory disease: specialist trials of vasoactive therapy, infusions, sympathetic procedures, or neuromodulation.

The literature explicitly states, “There is no single effective treatment for erythromelalgia,” and individualized, multidisciplinary management remains the expert consensus. (skeik2019erythromelalgia pages 1-2, algarni2025comparativeefficacyand pages 2-4)

Drug and intervention evidence

  • Aspirin: particularly effective in platelet-mediated MPN-associated secondary EM. Gastrointestinal bleeding, allergy, renal risk, and acquired von Willebrand disease in extreme thrombocytosis must be considered. Suggested NCIT intervention: aspirin therapy/antiplatelet therapy; CHEBI: aspirin.
  • Topical amitriptyline–ketamine: in a mixed 36-patient cohort, about 75% reported some pain relief: 3% complete, 39% substantial, and 33% some improvement. This is not a secondary-only response estimate. (algarni2025comparativeefficacyand pages 6-7)
  • Misoprostol: small controlled studies reported improvements in pain and temperature control, but diarrhea, abdominal pain, and nausea were frequent. (algarni2025comparativeefficacyand pages 6-7)
  • Iloprost: small studies reported improved cooling scores, sympathetic dysfunction, and disease severity; headache, flushing/erythema, and hypotension can occur. (algarni2025comparativeefficacyand pages 6-7)
  • Lidocaine: topical or intravenous use aims to stabilize hyperexcitable sensory fibers; experimental studies showed dose-dependent improvement in nociceptive thresholds. Cardiac and neurologic toxicity constrain systemic use. (algarni2025comparativeefficacyand pages 6-7, algarni2025comparativeefficacyand pages 2-4)
  • Other reported agents: gabapentin/pregabalin, amitriptyline, venlafaxine or other SNRIs, mexiletine, carbamazepine/oxcarbazepine, antihistamines, clonidine, and prostaglandin/vascular agents. Evidence is inconsistent and mostly uncontrolled.
  • Procedures: sympathetic blocks, epidural/local anesthetic techniques, chemical or surgical sympathectomy, botulinum toxin, and spinal-cord stimulation are rescue options with case-level or very small-study support.
  • Pediatric rescue evidence: one report described complete resolution in 4 of 5 patients receiving intravenous sodium nitroprusside, initially 1 µg/kg/min and titrated to 5 µg/kg/min; this is low-level evidence and not secondary-specific. (skeik2019erythromelalgia pages 2-3)

A 2025 systematic review found only six eligible studies, totaling 120 patients: iloprost n=8, misoprostol n=21, topical amitriptyline–ketamine n=36, lidocaine n=27, chemical lumbar sympathectomy n=13, and miscellaneous agents n=11. The small, mixed-etiology evidence base precludes a robust universal hierarchy. (algarni2025comparativeefficacyand pages 4-5, algarni2025comparativeefficacyand pages 1-2)

Recent developments and trials

  • EASE, NCT05917912: randomized double-blind Phase 2 crossover study of topical amitriptyline 15% (ATX01), 14 participants; began June 14, 2023 and completed February 29, 2024. Outcomes included attack pain, Brief Pain Inventory, EQ-5D, depression, and rescue cooling. Eligibility excluded important alternative neuropathic pain causes, limiting direct applicability to secondary EM. URL: https://clinicaltrials.gov/study/NCT05917912. (NCT05917912 chunk 1, NCT05917912 chunk 2)
  • Burst spinal-cord stimulation, NCT04039633: six-patient quadruple-blind crossover study, active but not recruiting; restricted to primary or idiopathic EM and excluded secondary disease. URL: https://clinicaltrials.gov/study/NCT04039633. (NCT04039633 chunk 1)
  • Earlier XPF-001, XPF-002, and PF-05089771 NaV1.7 programs enrolled primary/inherited EM, not secondary EM. URLs: https://clinicaltrials.gov/study/NCT01090622, https://clinicaltrials.gov/study/NCT01486446, and https://clinicaltrials.gov/study/NCT01769274. (NCT01090622 chunk 1, NCT01486446 chunk 2, NCT01769274 chunk 3)

Thus, a major 2023–2024 research gap is the continued exclusion or underrepresentation of secondary EM in interventional trials.

13. Prevention

There is no vaccine, population screening program, or proven pharmacologic primary prevention. Practical prevention is etiologic and tertiary:

  • Monitor blood counts when symptoms or risk factors suggest an MPN.
  • Control diabetes and treat reversible neuropathy causes.
  • Review and discontinue implicated medication when clinically safe.
  • Avoid excessive heat, prolonged standing, tight footwear, and unsafe direct-ice cooling.
  • Treat fissures or ulcers early and provide wound-care education.
  • Use genetic counseling only when the history suggests inherited primary EM; it is not routinely relevant to acquired secondary disease.

No evidence supports prophylactic aspirin for people without EM or an independent cardiovascular/hematologic indication.

14. Other species and natural disease

No well-validated naturally occurring veterinary equivalent of acquired secondary EM was identified. Consequently, no specific NCBI Taxon, breed/VBO association, zoonotic transmission, or cross-species prevalence can be assigned. The condition is not infectious or zoonotic as a syndrome.

SCN9A orthologs are evolutionarily conserved across mammals, but their relevance is primarily to nociception and inherited channelopathy. Platelet activation, microvascular thrombosis, diabetic neuropathy, and autonomic dysregulation can be studied in animals, but these reproduce components rather than the full human secondary-EM syndrome.

15. Model organisms and experimental systems

Human iPSC-derived sensory neurons carrying pathogenic SCN9A variants reproduce lowered firing thresholds and permit pharmacologic reversal of inherited EM phenotypes. These systems and NaV1.7 transgenic/knock-in models are valuable for pain-channel biology but model primary inherited EM, not secondary EM. The PF-05089771 program linked iPSC-derived sensory-neuron findings to a primary-EM trial, illustrating this translational application. (NCT01769274 chunk 3)

Potential component models include:

  • MPN or platelet-activation mouse models for thrombotic microvascular mechanisms.
  • Streptozotocin or genetic diabetes models for acquired small-fiber neuropathy.
  • Peripheral nerve injury/inflammation models for nociceptor hyperexcitability.
  • Endothelial-flow and microfluidic systems for capillary perfusion and thrombosis.

Their central limitation is failure to reproduce the defining human combination of heat-provoked erythema, thermoregulatory shunting, and severe distal burning pain. No dedicated, validated acquired secondary-EM mouse, rat, zebrafish, Drosophila, organoid, CRISPR-screen, or natural-animal model was identified.

Knowledge-base conclusions

Secondary erythromelalgia should be represented as an acquired clinical syndrome with multiple possible causal-disease relationships, not as an SCN9A disorder. Core phenotype assertions are well supported; secondary-specific epidemiology, molecular profiling, prognosis, and randomized-treatment evidence are sparse. The highest-priority implementation rules are: record the red-hot-burning attack phenotype; document heat/exercise/dependency triggers and cooling response; actively evaluate MPNs and neuropathies; annotate aspirin responsiveness specifically to platelet-mediated disease; and avoid transferring inherited-EM genetic claims or primary-only clinical-trial results to secondary EM.

References

  1. (assaad2025severeerythromelalgiapain pages 6-8): Wassim Assaad, Omar El Tarras, Soad Al Osta, and Chady Kallassy. Severe erythromelalgia pain attack in a young lebanese woman leading to hospitalization: a case report and literature review. Cureus, Sep 2025. URL: https://doi.org/10.7759/cureus.91530, doi:10.7759/cureus.91530. This article has 0 citations.

  2. (skeik2019erythromelalgia pages 2-3): Nedaa Skeik. Erythromelalgia. Harper's Textbook of Pediatric Dermatology, pages 1961-1964, Nov 2019. URL: https://doi.org/10.1002/9781119142812.ch151, doi:10.1002/9781119142812.ch151. This article has 1 citations.

  3. (algarni2025comparativeefficacyand pages 1-2): Abdullah S. Algarni, Reem M. Alharthi, Shaden O. Alqurashi, Ruba M. Alghanmi, Rimaz R. Aldawsari, Maysaa A. Alghamdi, and Ramy Samargandi. Comparative efficacy and tolerability of treatments for erythromelalgia: a systematic review. Medicina, 61:920, May 2025. URL: https://doi.org/10.3390/medicina61050920, doi:10.3390/medicina61050920. This article has 1 citations.

  4. (skeik2019erythromelalgia pages 1-2): Nedaa Skeik. Erythromelalgia. Harper's Textbook of Pediatric Dermatology, pages 1961-1964, Nov 2019. URL: https://doi.org/10.1002/9781119142812.ch151, doi:10.1002/9781119142812.ch151. This article has 1 citations.

  5. (algarni2025comparativeefficacyand pages 4-5): Abdullah S. Algarni, Reem M. Alharthi, Shaden O. Alqurashi, Ruba M. Alghanmi, Rimaz R. Aldawsari, Maysaa A. Alghamdi, and Ramy Samargandi. Comparative efficacy and tolerability of treatments for erythromelalgia: a systematic review. Medicina, 61:920, May 2025. URL: https://doi.org/10.3390/medicina61050920, doi:10.3390/medicina61050920. This article has 1 citations.

  6. (algarni2025comparativeefficacyand pages 6-7): Abdullah S. Algarni, Reem M. Alharthi, Shaden O. Alqurashi, Ruba M. Alghanmi, Rimaz R. Aldawsari, Maysaa A. Alghamdi, and Ramy Samargandi. Comparative efficacy and tolerability of treatments for erythromelalgia: a systematic review. Medicina, 61:920, May 2025. URL: https://doi.org/10.3390/medicina61050920, doi:10.3390/medicina61050920. This article has 1 citations.

  7. (algarni2025comparativeefficacyand pages 7-9): Abdullah S. Algarni, Reem M. Alharthi, Shaden O. Alqurashi, Ruba M. Alghanmi, Rimaz R. Aldawsari, Maysaa A. Alghamdi, and Ramy Samargandi. Comparative efficacy and tolerability of treatments for erythromelalgia: a systematic review. Medicina, 61:920, May 2025. URL: https://doi.org/10.3390/medicina61050920, doi:10.3390/medicina61050920. This article has 1 citations.

  8. (algarni2025comparativeefficacyand pages 2-4): Abdullah S. Algarni, Reem M. Alharthi, Shaden O. Alqurashi, Ruba M. Alghanmi, Rimaz R. Aldawsari, Maysaa A. Alghamdi, and Ramy Samargandi. Comparative efficacy and tolerability of treatments for erythromelalgia: a systematic review. Medicina, 61:920, May 2025. URL: https://doi.org/10.3390/medicina61050920, doi:10.3390/medicina61050920. This article has 1 citations.

  9. (NCT04039633 chunk 1): Spinal Cord Stimulation for Refractory Pain in Erythromelalgia. St. Olavs Hospital. 2019. ClinicalTrials.gov Identifier: NCT04039633

  10. (NCT05917912 chunk 1): EASE (Efficacy of ATX01 Study in Erythromelalgia). AlgoTherapeutix. 2023. ClinicalTrials.gov Identifier: NCT05917912

  11. (NCT05917912 chunk 2): EASE (Efficacy of ATX01 Study in Erythromelalgia). AlgoTherapeutix. 2023. ClinicalTrials.gov Identifier: NCT05917912

  12. (NCT01090622 chunk 1): Study of XPF-001 in the Treatment of Pain From Primary/Inherited Erythromelalgia (IEM). Xenon Pharmaceuticals Inc.. 2010. ClinicalTrials.gov Identifier: NCT01090622

  13. (NCT01486446 chunk 2): Phase 2a, Exploratory Study to Evaluate the Safety, Efficacy, Tolerability and Pharmacokinetics of XPF-002 in Patients With Primary/Inherited Erythromelalgia. Xenon Pharmaceuticals Inc.. 2011. ClinicalTrials.gov Identifier: NCT01486446

  14. (NCT01769274 chunk 3): Evaluation Of The Efficacy And Safety Of Single Doses Of PF-05089771 In Patients With Primary (Inherited) Erythromelalgia. Pfizer. 2012. ClinicalTrials.gov Identifier: NCT01769274

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