Psoriasis <-> Psoriatic Arthritis

Comorbidity A_BEFORE_B CANDIDATE

Cutaneous psoriasis and psoriatic arthritis are the paradigm case of a directed comorbidity within one disease family: in the large majority of patients the skin disease is established first and the musculoskeletal disease appears years later, which is what makes psoriasis clinics a practical screening population for incident PsA. The entry is deliberately curated as a comorbidity rather than folded into either disease entry, because the transition is not simply "psoriasis plus arthritis". MHC mapping that controls for age at psoriasis onset shows the classic psoriasis allele HLA-C*06:02 is *protective* against PsA relative to skin-only disease, while amino acid position 97 of HLA-B — the largest genetic effect in ankylosing spondylitis — is what distinguishes PsA. So the two conditions share an IL-23/IL-17 axis but not a single genetic architecture, and PsA sits partly with the spondyloarthritides. Not curated here: whether treating psoriasis prevents PsA. The observational signal for IL-23 blockade is suggestive but interception trials are ongoing, and asserting a preventive effect would go beyond what the cited sources claim.

Disease A

Psoriasis

Slug:Psoriasis

Disease B

Psoriatic Arthritis

Slug:Psoriatic_Arthritis

Causal Mechanism Graphs

Psoriasis

graph LR
    TYK2["TYK2"]
    Spesolimab["Spesolimab"]
    STAT3["STAT3"]
    IL_12_23_Inhibitor["IL-12/23 Inhibitor"]
    Sema4a_knockout_mouse["Sema4a knockout mouse"]
    TRAF3IP2["TRAF3IP2"]
    IL36RN["IL36RN"]
    Pustules["Pustules"]
    JAK_Inhibitors["JAK Inhibitors"]
    IL_23_Inhibitors["IL-23 Inhibitors"]
    IL23R["IL23R"]
    AP1S3["AP1S3"]
    IL12B["IL12B"]
    Outer_Biosciences_long_term_ex_vivo_human_skin_platform["Outer Biosciences long-term ex vivo human skin platform"]
    Keratinocyte_SEMA4A_Downregulation["Keratinocyte SEMA4A Downregulation"]
    IL_17_Inhibitors["IL-17 Inhibitors"]
    Epidermal_mTORC1_Activation["Epidermal mTORC1 Activation"]
    T_Cell_Mediated_Inflammation["T Cell-Mediated Inflammation"]
    Dendritic_Cell_Activation["Dendritic Cell Activation"]
    CARD14["CARD14"]
    IL_36_Keratinocyte_Activation["IL-36 Keratinocyte Activation"]
    IL1RL2["IL1RL2"]
    Keratinocyte_Hyperproliferation["Keratinocyte Hyperproliferation"]
    IL_23_IL_17_Axis["IL-23/IL-17 Axis"]

    T_Cell_Mediated_Inflammation --> Keratinocyte_Hyperproliferation
    Keratinocyte_SEMA4A_Downregulation --> Epidermal_mTORC1_Activation
    Keratinocyte_SEMA4A_Downregulation --> T_Cell_Mediated_Inflammation
    Epidermal_mTORC1_Activation --> Keratinocyte_Hyperproliferation
    Dendritic_Cell_Activation --> IL_23_IL_17_Axis
    IL_23_IL_17_Axis --> T_Cell_Mediated_Inflammation
    IL_36_Keratinocyte_Activation --> Pustules
    IL_17_Inhibitors --> IL_23_IL_17_Axis
    IL_23_Inhibitors --> IL_23_IL_17_Axis
    IL_12_23_Inhibitor --> IL_23_IL_17_Axis
    JAK_Inhibitors --> IL_23_IL_17_Axis
    Spesolimab --> IL_36_Keratinocyte_Activation
    Outer_Biosciences_long_term_ex_vivo_human_skin_platform --> IL_23_IL_17_Axis
    Outer_Biosciences_long_term_ex_vivo_human_skin_platform --> Keratinocyte_Hyperproliferation
    Outer_Biosciences_long_term_ex_vivo_human_skin_platform --> IL_23_IL_17_Axis
    Sema4a_knockout_mouse --> Keratinocyte_SEMA4A_Downregulation
    IL12B --> IL_23_IL_17_Axis
    IL23R --> IL_23_IL_17_Axis
    TYK2 --> IL_23_IL_17_Axis
    TRAF3IP2 --> IL_23_IL_17_Axis
    CARD14 --> Keratinocyte_Hyperproliferation
    IL36RN --> IL_36_Keratinocyte_Activation
    IL1RL2 --> IL_36_Keratinocyte_Activation
    AP1S3 --> IL_36_Keratinocyte_Activation
    STAT3 --> IL_23_IL_17_Axis

    style TYK2 fill:#f3e8ff
    style Spesolimab fill:#fce7f3
    style STAT3 fill:#f3e8ff
    style IL_12_23_Inhibitor fill:#fce7f3
    style Sema4a_knockout_mouse fill:#ede9fe
    style TRAF3IP2 fill:#f3e8ff
    style IL36RN fill:#f3e8ff
    style Pustules fill:#fef3c7
    style JAK_Inhibitors fill:#fce7f3
    style IL_23_Inhibitors fill:#fce7f3
    style IL23R fill:#f3e8ff
    style AP1S3 fill:#f3e8ff
    style IL12B fill:#f3e8ff
    style Outer_Biosciences_long_term_ex_vivo_human_skin_platform fill:#ccfbf1
    style Keratinocyte_SEMA4A_Downregulation fill:#dbeafe
    style IL_17_Inhibitors fill:#fce7f3
    style Epidermal_mTORC1_Activation fill:#dbeafe
    style T_Cell_Mediated_Inflammation fill:#dbeafe
    style Dendritic_Cell_Activation fill:#dbeafe
    style CARD14 fill:#f3e8ff
    style IL_36_Keratinocyte_Activation fill:#dbeafe
    style IL1RL2 fill:#f3e8ff
    style Keratinocyte_Hyperproliferation fill:#dbeafe
    style IL_23_IL_17_Axis fill:#dbeafe

Psoriatic Arthritis

graph LR
    Cytokine_Pathway_Activation["Cytokine Pathway Activation"]
    Innate_Immune_Activation_and_IL_17_Expressing_Mast_Cells["Innate Immune Activation and IL-17-Expressing Mast Cells"]

    Innate_Immune_Activation_and_IL_17_Expressing_Mast_Cells --> Cytokine_Pathway_Activation

    style Cytokine_Pathway_Activation fill:#dbeafe
    style Innate_Immune_Activation_and_IL_17_Expressing_Mast_Cells fill:#dbeafe

Association Signals

Signal 1

Population:Prospective cohort of 464 psoriasis patients without arthritis at enrollment (University of Toronto psoriasis cohort), followed 8 years, with PsA ascertained by CASPAR criteria.

Temporal: A before B: , B before A: , Same time:

INCIDENCE_RATE: 2.7

CI: 2.1 - 3.6

FDR:

Incident PsA per 100 psoriasis patients per year. The denominator is a psoriasis population followed forward with arthritis excluded at baseline, which is what a directed A_BEFORE_B risk signal requires; cross-sectional PsA-prevalence-among-psoriasis figures do not establish ordering.

PMID:26555117 (SUPPORT)

Source: HUMAN_CLINICAL

"The annual incidence rate of PsA was 2.7 cases (95% confidence interval 2.1-3.6) per 100 psoriasis patients."

Measures incident PsA prospectively in a psoriasis cohort free of arthritis at baseline, quantifying the directed risk.

Signal 2

Population:Psoriasis patients with arthralgia but without established PsA — the clinically defined at-risk stratum used in interception research.

Mapping notes:A narrative-review summary figure for an enriched at-risk subgroup, not a population rate; it is not comparable with the whole-cohort incidence above and is recorded to show how strongly arthralgia concentrates risk.

Temporal: A before B: , B before A: , Same time:

OTHER: 20.0

CI: -

FDR:

Approximate percentage of psoriasis patients with arthralgia who progress to PsA within 3 years.

PMID:42540001 (SUPPORT)

Source: HUMAN_CLINICAL

"progression from psoriasis with arthralgia to PsA occurs in ∼20% of patients within 3 years, typically manifesting with peripheral, synovitis-predominant presentations."

Quantifies short-term progression in the arthralgia-enriched at-risk subgroup and describes the phenotype of the transition.

Hypotheses

A shared IL-23/IL-17 cytokine axis operating in two different tissue compartments: the same pathway that sustains epidermal inflammation in psoriatic skin also drives inflammation at the enthesis and adjacent synovium, so the skin and joint diseases are two tissue expressions of one systemic immune program rather than independent conditions that happen to co-occur.

PMID:42540001 (SUPPORT)

Source: HUMAN_CLINICAL

"Converging immunopathogenic insights link skin and joint inflammation through interleukin (IL)-23/IL-17-driven pathways, enthesis-synovium crosstalk, and tissue-resident memory T-cell biology."

States the shared IL-23/IL-17 mechanism and the enthesis-synovium compartment linking skin disease to joint disease.

PMID:42540001 (SUPPORT)

Source: HUMAN_CLINICAL

"Psoriasis frequently precedes psoriatic arthritis (PsA), delineating a tractable window for disease interception."

Establishes the temporal ordering that this entry records as A_BEFORE_B.

Pathophysiology:

IL-23/IL-17 axis activation at the enthesis: IL-23-driven, IL-17-producing cells act at the enthesis and adjacent synovium, extending the cytokine program of psoriatic skin into musculoskeletal tissue.

Biological processes:

PMID:42540001 (SUPPORT)

Source: HUMAN_CLINICAL

"Converging immunopathogenic insights link skin and joint inflammation through interleukin (IL)-23/IL-17-driven pathways, enthesis-synovium crosstalk, and tissue-resident memory T-cell biology."

Names the IL-23 and IL-17 pathways as the shared mechanism operating at the enthesis-synovium interface.

Mechanical stress at entheseal insertion sites acts as the local trigger that converts a systemic psoriatic predisposition into overt joint disease — the "deep Koebner" phenomenon, an internal counterpart of the cutaneous Koebner response to skin trauma. This offers an explanation for why only a minority of psoriasis patients progress, and why progression is entheseal and asymmetric rather than symmetrically polyarticular.

PMID:21715249 (SUPPORT)

Source: HUMAN_CLINICAL

"The triggering role of physical stress is seen in the "deep Koebner" phenomenon, which causes inflammation in the synovial membrane and in enthesis, resulting in peripheral arthritis."

States the deep Koebner mechanism: physical stress at the enthesis and synovium producing peripheral arthritis in psoriatic disease.

The two conditions are not genetically interchangeable. Once age at psoriasis onset is controlled for, the canonical psoriasis risk allele HLA-C*06:02 is associated with skin-only disease and is protective against PsA, while the discriminating signal is amino acid position 97 of HLA-B — the same position carrying the largest genetic effect in ankylosing spondylitis. PsA is therefore better read as a spondyloarthritis arising on a psoriatic background than as a later stage of psoriasis, and the comorbidity is partly a shared-susceptibility relationship rather than a pure progression.

PMID:28821532 (SUPPORT)

Source: HUMAN_CLINICAL

"HLA-C*06:02 was protective of PsA compared to PsC (p=9.57×10-66, OR 0.37)."

Shows the principal psoriasis susceptibility allele runs in the opposite direction for PsA relative to cutaneous-only psoriasis.

PMID:28821532 (SUPPORT)

Source: HUMAN_CLINICAL

"amino acid position 97 of HLA-B differentiates PsA from PsC. This amino acid also represents the largest genetic effect for ankylosing spondylitis, thereby refining the genetic overlap of these two spondyloarthropathies."

Identifies the MHC signal specific to joint involvement and ties it to the spondyloarthritis susceptibility architecture.

Raw YAML

Show YAML

name: com_Psoriasis__Psoriatic_Arthritis
creation_date: "2026-08-27T00:00:00Z"
curation_status: CANDIDATE
notes: >-
  Cutaneous psoriasis and psoriatic arthritis are the paradigm case of a
  directed comorbidity within one disease family: in the large majority of
  patients the skin disease is established first and the musculoskeletal
  disease appears years later, which is what makes psoriasis clinics a
  practical screening population for incident PsA.

  The entry is deliberately curated as a comorbidity rather than folded into
  either disease entry, because the transition is not simply "psoriasis plus
  arthritis". MHC mapping that controls for age at psoriasis onset shows the
  classic psoriasis allele HLA-C*06:02 is *protective* against PsA relative to
  skin-only disease, while amino acid position 97 of HLA-B — the largest
  genetic effect in ankylosing spondylitis — is what distinguishes PsA. So the
  two conditions share an IL-23/IL-17 axis but not a single genetic
  architecture, and PsA sits partly with the spondyloarthritides.

  Not curated here: whether treating psoriasis prevents PsA. The observational
  signal for IL-23 blockade is suggestive but interception trials are ongoing,
  and asserting a preventive effect would go beyond what the cited sources
  claim.

disease_a:
  slug: Psoriasis
  preferred_term: psoriasis
  term:
    id: MONDO:0005083
    label: psoriasis

disease_b:
  slug: Psoriatic_Arthritis
  preferred_term: psoriatic arthritis
  term:
    id: MONDO:0011849
    label: psoriatic arthritis

directionality: A_BEFORE_B
effect_direction: RISK

hypotheses:
- description: >-
    A shared IL-23/IL-17 cytokine axis operating in two different tissue
    compartments: the same pathway that sustains epidermal inflammation in
    psoriatic skin also drives inflammation at the enthesis and adjacent
    synovium, so the skin and joint diseases are two tissue expressions of one
    systemic immune program rather than independent conditions that happen to
    co-occur.
  evidence:
  - reference: PMID:42540001
    reference_title: Does effective therapy of psoriasis prevent the development of psoriatic arthritis?
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Converging immunopathogenic insights link skin and joint inflammation through interleukin (IL)-23/IL-17-driven pathways, enthesis-synovium crosstalk, and tissue-resident memory T-cell biology."
    explanation: >-
      States the shared IL-23/IL-17 mechanism and the enthesis-synovium
      compartment linking skin disease to joint disease.
  - reference: PMID:42540001
    reference_title: Does effective therapy of psoriasis prevent the development of psoriatic arthritis?
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Psoriasis frequently precedes psoriatic arthritis (PsA), delineating a tractable window for disease interception."
    explanation: >-
      Establishes the temporal ordering that this entry records as A_BEFORE_B.
  pathophysiology:
  - name: IL-23/IL-17 axis activation at the enthesis
    description: >-
      IL-23-driven, IL-17-producing cells act at the enthesis and adjacent
      synovium, extending the cytokine program of psoriatic skin into
      musculoskeletal tissue.
    biological_processes:
    - preferred_term: interleukin-23-mediated signaling
      term:
        id: GO:0038155
        label: interleukin-23-mediated signaling pathway
      modifier: INCREASED
    - preferred_term: interleukin-17-mediated signaling
      term:
        id: GO:0097400
        label: interleukin-17-mediated signaling pathway
      modifier: INCREASED
    evidence:
    - reference: PMID:42540001
      reference_title: Does effective therapy of psoriasis prevent the development of psoriatic arthritis?
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Converging immunopathogenic insights link skin and joint inflammation through interleukin (IL)-23/IL-17-driven pathways, enthesis-synovium crosstalk, and tissue-resident memory T-cell biology."
      explanation: >-
        Names the IL-23 and IL-17 pathways as the shared mechanism operating at
        the enthesis-synovium interface.

- description: >-
    Mechanical stress at entheseal insertion sites acts as the local trigger
    that converts a systemic psoriatic predisposition into overt joint disease
    — the "deep Koebner" phenomenon, an internal counterpart of the cutaneous
    Koebner response to skin trauma. This offers an explanation for why only a
    minority of psoriasis patients progress, and why progression is entheseal
    and asymmetric rather than symmetrically polyarticular.
  evidence:
  - reference: PMID:21715249
    reference_title: "Psoriatic arthritis: from a dermatological perspective."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The triggering role of physical stress is seen in the \"deep Koebner\" phenomenon, which causes inflammation in the synovial membrane and in enthesis, resulting in peripheral arthritis."
    explanation: >-
      States the deep Koebner mechanism: physical stress at the enthesis and
      synovium producing peripheral arthritis in psoriatic disease.

- description: >-
    The two conditions are not genetically interchangeable. Once age at
    psoriasis onset is controlled for, the canonical psoriasis risk allele
    HLA-C*06:02 is associated with skin-only disease and is protective against
    PsA, while the discriminating signal is amino acid position 97 of HLA-B —
    the same position carrying the largest genetic effect in ankylosing
    spondylitis. PsA is therefore better read as a spondyloarthritis arising on
    a psoriatic background than as a later stage of psoriasis, and the
    comorbidity is partly a shared-susceptibility relationship rather than a
    pure progression.
  evidence:
  - reference: PMID:28821532
    reference_title: Cross-phenotype association mapping of the MHC identifies genetic variants that differentiate psoriatic arthritis from psoriasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HLA-C*06:02 was protective of PsA compared to PsC (p=9.57×10-66, OR 0.37)."
    explanation: >-
      Shows the principal psoriasis susceptibility allele runs in the opposite
      direction for PsA relative to cutaneous-only psoriasis.
  - reference: PMID:28821532
    reference_title: Cross-phenotype association mapping of the MHC identifies genetic variants that differentiate psoriatic arthritis from psoriasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "amino acid position 97 of HLA-B differentiates PsA from PsC. This amino acid also represents the largest genetic effect for ankylosing spondylitis, thereby refining the genetic overlap of these two spondyloarthropathies."
    explanation: >-
      Identifies the MHC signal specific to joint involvement and ties it to
      the spondyloarthritis susceptibility architecture.

association_signals:
- source: LITERATURE
  method: LITERATURE_ASSOCIATION
  population: >-
    Prospective cohort of 464 psoriasis patients without arthritis at
    enrollment (University of Toronto psoriasis cohort), followed 8 years, with
    PsA ascertained by CASPAR criteria.
  directionality: A_BEFORE_B
  effect_direction: RISK
  statistics:
    metrics:
    - metric_type: INCIDENCE_RATE
      metric_value: 2.7
      metric_ci_lower: 2.1
      metric_ci_upper: 3.6
      notes: >-
        Incident PsA per 100 psoriasis patients per year. The denominator is a
        psoriasis population followed forward with arthritis excluded at
        baseline, which is what a directed A_BEFORE_B risk signal requires;
        cross-sectional PsA-prevalence-among-psoriasis figures do not establish
        ordering.
    evidence:
    - reference: PMID:26555117
      reference_title: "The Incidence and Risk Factors for Psoriatic Arthritis in Patients With Psoriasis: A Prospective Cohort Study."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The annual incidence rate of PsA was 2.7 cases (95% confidence interval 2.1-3.6) per 100 psoriasis patients."
      explanation: >-
        Measures incident PsA prospectively in a psoriasis cohort free of
        arthritis at baseline, quantifying the directed risk.

- source: LITERATURE
  method: LITERATURE_ASSOCIATION
  population: >-
    Psoriasis patients with arthralgia but without established PsA — the
    clinically defined at-risk stratum used in interception research.
  directionality: A_BEFORE_B
  effect_direction: RISK
  mapping_notes: >-
    A narrative-review summary figure for an enriched at-risk subgroup, not a
    population rate; it is not comparable with the whole-cohort incidence
    above and is recorded to show how strongly arthralgia concentrates risk.
  statistics:
    metrics:
    - metric_type: OTHER
      metric_value: 20.0
      notes: >-
        Approximate percentage of psoriasis patients with arthralgia who
        progress to PsA within 3 years.
    evidence:
    - reference: PMID:42540001
      reference_title: Does effective therapy of psoriasis prevent the development of psoriatic arthritis?
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "progression from psoriasis with arthralgia to PsA occurs in ∼20% of patients within 3 years, typically manifesting with peripheral, synovitis-predominant presentations."
      explanation: >-
        Quantifies short-term progression in the arthralgia-enriched at-risk
        subgroup and describes the phenotype of the transition.

Source:GitHub