Idiopathic hypersomnia is a central disorder of hypersomnolence defined by irrepressible daytime sleepiness that persists despite normal or long nocturnal sleep, in the absence of any identifiable cause. It is a diagnosis of exclusion, and unusually among the entries in this knowledge base its mechanism is genuinely unknown - the disorder is named for that ignorance. What distinguishes it clinically is not the sleepiness, which it shares with every other hypersomnolence disorder, but its quality: sleep is prolonged and unrefreshing rather than fragmented, naps are long and non-restorative rather than brief and restorative as in narcolepsy, and waking is dominated by severe and prolonged sleep inertia (sleep drunkenness) - a difficulty in achieving full alertness after waking that patients frequently rate as more disabling than the sleepiness itself. Cerebrospinal fluid hypocretin-1 is normal by definition, which excludes the orexin-deficiency mechanism of narcolepsy type 1 and makes idiopathic hypersomnia the principal negative case against that module. The leading positive hypothesis runs in the opposite direction - a substance in cerebrospinal fluid that potentiates GABA-A receptor signalling, i.e. excessive somnogenic inhibition rather than deficient arousal drive - but that finding has not been robustly replicated and the entry curates it as an unconfirmed hypothesis rather than as the mechanism.
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name: Idiopathic Hypersomnia
creation_date: "2026-08-24T00:00:00Z"
category: Neurological Disorder
parents:
- Sleep Disorder
- Neurological Disease
disease_term:
preferred_term: idiopathic hypersomnia
term:
id: MONDO:0018044
label: idiopathic hypersomnia
description: >-
Idiopathic hypersomnia is a central disorder of hypersomnolence defined by
irrepressible daytime sleepiness that persists despite normal or long
nocturnal sleep, in the absence of any identifiable cause. It is a diagnosis
of exclusion, and unusually among the entries in this knowledge base its
mechanism is genuinely unknown - the disorder is named for that ignorance.
What distinguishes it clinically is not the sleepiness, which it shares with
every other hypersomnolence disorder, but its quality: sleep is prolonged and
unrefreshing rather than fragmented, naps are long and non-restorative rather
than brief and restorative as in narcolepsy, and waking is dominated by severe
and prolonged sleep inertia (sleep drunkenness) - a difficulty in achieving
full alertness after waking that patients frequently rate as more disabling
than the sleepiness itself. Cerebrospinal fluid hypocretin-1 is normal by
definition, which excludes the orexin-deficiency mechanism of narcolepsy type
1 and makes idiopathic hypersomnia the principal negative case against that
module. The leading positive hypothesis runs in the opposite direction - a
substance in cerebrospinal fluid that potentiates GABA-A receptor signalling,
i.e. excessive somnogenic inhibition rather than deficient arousal drive - but
that finding has not been robustly replicated and the entry curates it as an
unconfirmed hypothesis rather than as the mechanism.
notes: >-
Two curatorial decisions in this entry are deliberate and should be preserved.
(1) NO CONFORMANCE TO orexin_arousal_instability. Idiopathic hypersomnia is
the module's stated negative boundary: hypersomnolence alone does not license
conformance, and these patients have normal CSF hypocretin-1 as a diagnostic
requirement. The module is referenced here only for contrast.
(2) THE MECHANISM IS CURATED AS UNKNOWN, with a named candidate. The
pathophysiology chain below is built around what is actually established -
hypersomnolence with preserved and often extended sleep, and severe sleep
inertia - with the GABA-A potentiation finding attached as an EMERGING
mechanistic hypothesis carrying its own replication gap, not as the trigger
node. Resist the temptation to promote it: it rests substantially on a single
laboratory's assay, the identity of the bioactive substance was never
established, and the flumazenil response that supported it was open-label in
seven patients.
has_subtypes:
- name: IH with long sleep time
display_name: Idiopathic hypersomnia with long sleep time
description: >-
Habitual nocturnal sleep of 10 hours or more (ICSD-2 criterion), typically
with very severe sleep inertia and unrefreshing long naps. Retained here as
a named subtype because it was a formal ICSD-2 category and because
treatment trials have been stratified by it, but see the discussion on
subtype validity: ICSD-3 abandoned the split.
evidence:
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
the description of idiopathic hypersomnia with two forms, polysymptomatic
and monosymptomatic, by the same Bedrich Roth in 1976
explanation: >-
Documents the historical two-form division from which the long-sleep and
non-long-sleep subtypes descend.
- name: IH without long sleep time
display_name: Idiopathic hypersomnia without long sleep time
description: >-
Nocturnal sleep of normal duration with a mean sleep latency of 8 minutes or
less on the multiple sleep latency test and fewer than two sleep-onset REM
periods. This is the subtype in which the two randomised modafinil trials
were conducted, and the subtype whose boundary with narcolepsy type 2 is
least secure.
evidence:
- reference: PMID:33631500
reference_title: "Efficacy and safety of modafinil in patients with idiopathic hypersomnia without long sleep time: a multicenter, randomized, double-blind, placebo-controlled, parallel-group comparison study."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Modafinil, an established treatment for narcolepsy, was tested for efficacy
and safety in Japanese patients with IH without long sleep time.
explanation: >-
Confirms this subtype as a distinct trial population, which is the main
operational reason the split is retained here.
pathophysiology:
- name: Unidentified Somnogenic Process
description: >-
The trigger node, and it is deliberately named for what is not known. No
structural lesion, neurotransmitter deficiency, autoimmune target, or
causative gene has been established in idiopathic hypersomnia. What is
established is negative and constraining: CSF hypocretin-1 is normal, which
excludes the orexin-deficiency mechanism; there is no HLA association of the
strength seen in narcolepsy type 1; and no consistent neuropathology has
been reported. Onset is typically in adolescence or young adulthood, a
familial background is frequently reported but has never been rigorously
characterised, and no biological marker exists. Curating this node as
unknown rather than assigning it a plausible mechanism is the honest
position and is what the disorder's name records.
role: trigger
biological_scale: ORGANISM
evidence:
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Yet, MSLT is neither sensitive nor specific and the polysomnographic
diagnostic criteria require continuous readjustment and biologic markers
are still lacking.
explanation: >-
States the absence of a biological marker directly, which is the evidence
for curating this node as an unidentified process rather than assigning it
a mechanism.
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
A familial background is often present but rigorous studies are still
lacking.
explanation: >-
Records the familial signal and, in the same sentence, that it has not
been characterised - so this entry curates no inheritance mechanism.
- reference: PMID:12374492
reference_title: The role of cerebrospinal fluid hypocretin measurement in the diagnosis of narcolepsy and other hypersomnias.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Healthy controls and subjects with other sleep disorders all had normal levels.
explanation: >-
Establishes the key negative constraint on this node - normal CSF
hypocretin-1 in hypersomnias other than narcolepsy-cataplexy - which is
why this entry does not conform to orexin_arousal_instability.
downstream:
- target: Increased Homeostatic Sleep Drive with Preserved Sleep Continuity
description: >-
Whatever the somnogenic process is, its measurable effect is an increase in
sleep propensity that does not degrade sleep quality or continuity.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- target: Impaired Arousal from Sleep (Sleep Inertia)
description: >-
The same unidentified process is presumed to underlie the difficulty in
transitioning out of sleep, which does not follow from sleep drive alone.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
hypothesis_groups:
- gabaergic_potentiation
- name: Increased Homeostatic Sleep Drive with Preserved Sleep Continuity
description: >-
The central and defining physiological abnormality: sleep propensity is
pathologically elevated, but sleep architecture, efficiency, and continuity
are normal or better than normal. This combination is what separates
idiopathic hypersomnia from every other cause of daytime sleepiness. In
narcolepsy type 1 the sleep-wake switch is unstable in both directions, so
nocturnal sleep is fragmented; in sleep-disordered breathing it is destroyed
by respiratory events; in circadian disorders it is displaced in time. Here
sleep is abundant, consolidated, and still insufficient. Sleep is extended
rather than curtailed, and the extension does not relieve the sleepiness -
which is the observation that makes a simple sleep-debt model untenable.
role: central_effector
biological_scale: ORGANISM
biological_processes:
- preferred_term: sleep
term:
id: GO:0030431
label: sleep
modifier: INCREASED
- preferred_term: regulation of the sleep/wake cycle
term:
id: GO:0042749
label: regulation of circadian sleep/wake cycle
modifier: ABNORMAL
evidence:
- reference: PMID:36921459
reference_title: "Update on the treatment of idiopathic hypersomnia: Progress, challenges, and expert opinion."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Idiopathic hypersomnia is a central hypersomnolence disorder of unknown
origin characterized by excessive daytime sleepiness despite normal or
long sleep time, and frequent severe sleep inertia.
explanation: >-
States both halves of this node - pathological sleepiness coexisting with
normal or increased sleep - which is the combination that defines the
disorder.
- reference: PMID:38165322
reference_title: Prevalence and Course of Idiopathic Hypersomnia in the Wisconsin Sleep Cohort Study.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
cases with IH had more severe sleepiness and sleep propensity, despite
similar or longer sleep times
explanation: >-
Population-cohort confirmation with objective polysomnography and multiple
sleep latency testing that the sleepiness is not explained by reduced
sleep, which is what the node asserts.
downstream:
- target: Non-Restorative Long Sleep and Unrefreshing Naps
description: >-
Elevated sleep drive that is not discharged by sleep produces prolonged
sleep episodes and long naps from which the patient does not wake refreshed.
causal_link_type: DIRECT
- name: Impaired Arousal from Sleep (Sleep Inertia)
description: >-
A partly separable abnormality, and one that a pure sleep-drive model does
not predict. Waking is prolonged, confused, and incomplete: patients are
difficult to rouse, may require multiple alarms or another person, and remain
impaired for tens of minutes to hours after rising - the "sleep drunkenness"
Roth described in the original 1956 account. It is curated as its own node
because it dissociates from sleepiness in treatment response as well as in
phenomenology, and because it, rather than the sleepiness, is often the most
disabling symptom and the one that most reliably distinguishes idiopathic
hypersomnia from narcolepsy at the bedside.
role: effector
biological_scale: ORGANISM
biological_processes:
- preferred_term: sleep/wake cycle state transition to wakefulness
term:
id: GO:0022410
label: circadian sleep/wake cycle process
modifier: ABNORMAL
evidence:
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
It is often accompanied by sleep of long duration and debilitating sleep
inertia.
explanation: >-
Names sleep inertia as a defining accompaniment of the disorder rather
than an incidental feature, supporting its curation as a separate node.
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Idiopathic hypersomnia continues to evolve from the concept of "sleep
drunkenness" introduced by Bedrich Roth in Prague in 1956
explanation: >-
Documents that the arousal abnormality, not the sleepiness, was the
founding observation of the disease concept.
downstream:
- target: Chronic Functional Impairment
description: >-
Prolonged post-waking impairment interferes with employment, education,
and driving independently of the daytime sleepiness.
causal_link_type: DIRECT
- name: Non-Restorative Long Sleep and Unrefreshing Naps
description: >-
Sleep in idiopathic hypersomnia fails at its restorative function while
succeeding at its structural one. Nocturnal sleep may extend well beyond ten
hours, and daytime naps - which in narcolepsy are short and briefly
restorative - are here long and leave the patient no better. This is the
feature clinicians use to separate the two disorders in the consulting room,
and it constrains any candidate mechanism: whatever is wrong is not a failure
to obtain sleep but a failure of obtained sleep to discharge sleep pressure.
role: effector
biological_scale: ORGANISM
biological_processes:
- preferred_term: sleep
term:
id: GO:0030431
label: sleep
modifier: ABNORMAL
evidence:
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
as well as a 24 h PSG or a 2-wk actigraphy in association with a sleep log
to ensure a total 24-h sleep time longer than or equal to 66O minutes
explanation: >-
Gives the operational threshold (a 24-hour sleep time of at least 660
minutes) by which extended sleep is established, which is how this node is
measured. Note the source text contains a typographic error, printing the
letter O for the final zero of "660"; the snippet reproduces the cached
text verbatim as required and the correct value is 660 minutes.
downstream:
- target: Chronic Functional Impairment
description: >-
Long unrefreshing sleep consumes the day and does not relieve the
sleepiness, compounding disability.
causal_link_type: DIRECT
- name: Chronic Functional Impairment
description: >-
The clinical endpoint. Idiopathic hypersomnia is most often a chronic
condition of adolescent or young-adult onset with substantial occupational,
educational, and social disability - sometimes rated by patients as greater
than that of narcolepsy, in part because the disorder is less recognised and
its severity less readily believed. It is not, however, uniformly permanent:
in the only population-based longitudinal series, pathological somnolence
remitted in roughly 40% of cases over about twelve years, which is a
prognostically important finding and one that any mechanistic account must
accommodate.
role: consequence
biological_scale: ORGANISM
evidence:
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
The condition is disabling, sometimes even more so than narcolepsy type 1
or 2.
explanation: >-
Establishes the magnitude of disability relative to the better-recognised
comparator disorder.
- reference: PMID:38165322
reference_title: Prevalence and Course of Idiopathic Hypersomnia in the Wisconsin Sleep Cohort Study.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Longitudinal data (spanning 12.1 ± 4.3 years) demonstrated a chronic course
of sleepiness for most of the cases with IH, though pathologic somnolence
remitted in roughly 40% of cases.
explanation: >-
Quantifies both the chronicity and the substantial remission rate, which
together define the natural history recorded at this node.
mechanistic_hypotheses:
- hypothesis_group_id: gabaergic_potentiation
hypothesis_label: Endogenous GABA-A Receptor Potentiation
status: EMERGING
description: >-
The leading positive hypothesis, and the reason idiopathic hypersomnia is
sometimes described as the mirror image of narcolepsy. Cerebrospinal fluid
from hypersomnolent patients was reported to potentiate GABA-A receptor
function in vitro in the presence of GABA, with the bioactivity attributable
to a trypsin-sensitive component of 500-3000 daltons whose identity was never
established. On this model the disorder is one of excessive endogenous
somnogenic inhibition rather than deficient arousal drive - which would
explain why it coexists with normal orexin, why sleep is abundant rather than
fragmented, and why arousal from sleep is specifically impaired. The
supporting flumazenil result is mechanistically striking, since flumazenil is
conventionally regarded as lacking intrinsic activity, and it reversed the
enhancement in vitro and normalised vigilance in an open-label series of
seven patients. It is curated as EMERGING and not as the mechanism: the
finding rests substantially on one laboratory's assay, the bioactive
substance was never identified, and the clinical arm was small and unblinded.
evidence:
- reference: PMID:23175709
reference_title: Modulation of vigilance in the primary hypersomnias by endogenous enhancement of GABAA receptors.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
We conclude that a naturally occurring substance in CSF augments inhibitory
GABA signaling, thus revealing a new pathophysiology associated with
excessive daytime sleepiness.
explanation: >-
The primary claim of the hypothesis, stated by its originators, and the
basis for curating it as a candidate mechanism.
- reference: PMID:23175709
reference_title: Modulation of vigilance in the primary hypersomnias by endogenous enhancement of GABAA receptors.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Furthermore, flumazenil normalized vigilance in seven hypersomnolent
patients.
explanation: >-
Cited as PARTIAL because it is the clinical arm of the hypothesis and is
an open-label observation in seven patients - suggestive, and explicitly
not sufficient to establish the mechanism.
- reference: PMID:23175709
reference_title: Modulation of vigilance in the primary hypersomnias by endogenous enhancement of GABAA receptors.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
The bioactive CSF component had a mass of 500 to 3000 daltons and was
neutralized by trypsin.
explanation: >-
Records how far characterisation of the putative somnogen got - a mass
range and protease sensitivity - and therefore that no molecular identity
was established, which is the principal reason the hypothesis remains
EMERGING.
phenotypes:
- category: Neurological
name: Excessive Daytime Sleepiness
description: >-
Irrepressible daytime sleepiness present daily for at least three months,
with a mean sleep latency of 8 minutes or less on the multiple sleep latency
test or a documented 24-hour sleep time of at least 660 minutes. Unlike the
sleep attacks of narcolepsy it is typically continuous rather than episodic.
phenotype_term:
preferred_term: Excessive daytime somnolence
term:
id: HP:0001262
label: Excessive daytime somnolence
temporality: CHRONIC
frequency: OBLIGATE
evidence:
- reference: PMID:36921459
reference_title: "Update on the treatment of idiopathic hypersomnia: Progress, challenges, and expert opinion."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Idiopathic hypersomnia is a central hypersomnolence disorder of unknown
origin characterized by excessive daytime sleepiness despite normal or
long sleep time, and frequent severe sleep inertia.
explanation: >-
Excessive daytime sleepiness is the defining diagnostic criterion, so the
frequency band is OBLIGATE by definition rather than by observation.
- category: Neurological
name: Severe Sleep Inertia (Sleep Drunkenness)
description: >-
Prolonged difficulty achieving full alertness on waking, with confusion,
ataxia, irritability and automatic behaviour lasting from tens of minutes to
hours. Frequently the most disabling symptom, and the historical founding
observation of the disease concept.
phenotype_term:
preferred_term: Sleep drunkenness
term:
id: HP:6000456
label: Sleep drunkeness
severity: SEVERE
frequency: FREQUENT
evidence:
- reference: PMID:36921459
reference_title: "Update on the treatment of idiopathic hypersomnia: Progress, challenges, and expert opinion."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
characterized by excessive daytime sleepiness despite normal or long sleep
time, and frequent severe sleep inertia
explanation: >-
Supports the FREQUENT band directly: the source characterises severe sleep
inertia as frequent in the disorder, which maps to the FREQUENT enum tier
rather than to an obligate or occasional one.
- category: Neurological
name: Prolonged Nocturnal Sleep
description: >-
Habitual nocturnal sleep beyond normal duration, with a total 24-hour sleep
time of 660 minutes or more in the long-sleep subtype, from which the patient
still wakes unrefreshed.
subtype: IH with long sleep time
phenotype_term:
preferred_term: Sleep disturbance
term:
id: HP:0002360
label: Sleep disturbance
evidence:
- reference: PMID:38165322
reference_title: Prevalence and Course of Idiopathic Hypersomnia in the Wisconsin Sleep Cohort Study.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
cases with IH had more severe sleepiness and sleep propensity, despite
similar or longer sleep times
explanation: >-
Objective cohort evidence for preserved or extended sleep duration in this
disorder; frequency deliberately omitted, since the source does not
quantify how many patients meet the long-sleep threshold.
- category: Neurological
name: Unrefreshing Long Naps
description: >-
Daytime naps that are long (often over an hour) and leave the patient no more
alert - in explicit contrast to the short, briefly restorative naps
characteristic of narcolepsy, which is the most useful bedside discriminator
between the two disorders.
phenotype_term:
preferred_term: Excessive daytime somnolence
term:
id: HP:0001262
label: Excessive daytime somnolence
evidence:
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
The key manifestation is hypersomnolence.
explanation: >-
Supports hypersomnolence as the core manifestation this phenotype
elaborates; the nap-quality contrast itself is stated in the description
and not claimed from this snippet, and no frequency band is asserted.
diagnosis:
- name: Polysomnography followed by multiple sleep latency test
description: >-
Overnight polysomnography to exclude other causes of hypersomnolence
(particularly sleep-disordered breathing and insufficient sleep), followed by
a multiple sleep latency test demonstrating a mean sleep latency of 8 minutes
or less with fewer than two sleep-onset REM periods. The two-SOREMP threshold
is what separates idiopathic hypersomnia from narcolepsy type 2, and it is a
weak boundary - see the discussion on entity validity.
evidence:
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Polysomnography (PSG) followed by a multiple sleep latency test (MSLT) is
mandatory
explanation: >-
Establishes the mandatory diagnostic sequence.
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Yet, MSLT is neither sensitive nor specific and the polysomnographic
diagnostic criteria require continuous readjustment
explanation: >-
Cited as PARTIAL because it qualifies the same test it recommends: the
diagnostic standard is mandatory but acknowledged to be neither sensitive
nor specific, which is why this entry does not treat a positive MSLT as
establishing a mechanism.
- name: Extended polysomnography or actigraphy with sleep log
description: >-
A 24-hour polysomnogram, or two weeks of actigraphy with a concurrent sleep
log, to document a total 24-hour sleep time of at least 660 minutes. This is
the alternative diagnostic route when the mean sleep latency exceeds 8
minutes, and it is the route that captures the long-sleep presentation, which
the multiple sleep latency test systematically misses.
diagnosis_term:
preferred_term: actigraphy
term:
id: NCIT:C180883
label: Actigraphy
evidence:
- reference: PMID:26599679
reference_title: Idiopathic hypersomnia.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
as well as a 24 h PSG or a 2-wk actigraphy in association with a sleep log
to ensure a total 24-h sleep time longer than or equal to 66O minutes, when
the mean sleep latency on the MSLT is longer than 8 min
explanation: >-
Specifies the alternative diagnostic pathway and the circumstance in which
it applies. The cached source prints the letter O for the final zero of
"660"; the snippet is reproduced verbatim as required and the intended
threshold is 660 minutes.
- name: Cerebrospinal fluid hypocretin-1 measurement
description: >-
Not required for diagnosis, but decisive where narcolepsy type 1 is in the
differential: a normal CSF hypocretin-1 level is expected in idiopathic
hypersomnia and a level below 110 pg/mL reclassifies the patient as
narcolepsy type 1 regardless of the presence or absence of cataplexy.
evidence:
- reference: PMID:12374492
reference_title: The role of cerebrospinal fluid hypocretin measurement in the diagnosis of narcolepsy and other hypersomnias.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Hypocretin-1 levels below 110 pg/mL were diagnostic for narcolepsy.
explanation: >-
Gives the threshold that excludes this diagnosis, which is the reason the
test is listed here despite not being a positive criterion.
- reference: PMID:12374492
reference_title: The role of cerebrospinal fluid hypocretin measurement in the diagnosis of narcolepsy and other hypersomnias.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Ten subjects with hypersomnia had intermediate levels
explanation: >-
Cited as PARTIAL because it records the boundary case the clean threshold
obscures: a minority of hypersomnolent patients fall in the intermediate
range and are classified by neither rule.
treatments:
- name: Modafinil
description: >-
A wake-promoting agent and the most commonly used treatment, prescribed
off-label in most jurisdictions since its European idiopathic hypersomnia
indication was withdrawn in 2011. It improves objective and subjective
sleepiness but is not directed at sleep inertia, which is the symptom
patients most often rate as most disabling - a therapeutic gap this entry
records deliberately.
therapeutic_modality: SMALL_MOLECULE
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: modafinil
term:
id: CHEBI:31859
label: modafinil
target_mechanisms:
- target: Increased Homeostatic Sleep Drive with Preserved Sleep Continuity
treatment_effect: INHIBITS
description: >-
Wake promotion opposes the elevated sleep propensity symptomatically; it
does not act on the unidentified upstream process and is not
disease-modifying.
evidence:
- reference: PMID:33631500
reference_title: "Efficacy and safety of modafinil in patients with idiopathic hypersomnia without long sleep time: a multicenter, randomized, double-blind, placebo-controlled, parallel-group comparison study."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Patients treated with modafinil experienced a significantly prolonged mean
sleep latency on the MWT at the end of the study compared with placebo
explanation: >-
Randomised placebo-controlled evidence of objective benefit on daytime
wakefulness in the subtype studied.
- reference: PMID:36921459
reference_title: "Update on the treatment of idiopathic hypersomnia: Progress, challenges, and expert opinion."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Modafinil, which was approved for idiopathic hypersomnia until 2011 in
Europe, is the most commonly used treatment and improved sleepiness in two
recent randomized placebo-controlled trials.
explanation: >-
Establishes modafinil's place in practice and that two randomised trials
support it, while recording its off-label regulatory status.
- name: Low-Sodium Oxybate
description: >-
The only agent approved specifically for idiopathic hypersomnia (United
States, 2021). Notable mechanistically as well as clinically, because it
reduces sleep inertia as well as daytime sleepiness - the only treatment
shown to act on both nodes - and because a GABA-B agonist improving a
disorder hypothesised to involve excessive GABA-A potentiation is a genuine
puzzle that the entry's mechanistic hypothesis does not resolve.
therapeutic_modality: SMALL_MOLECULE
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: sodium oxybate
term:
id: CHEBI:749298
label: sodium oxybate
target_mechanisms:
- target: Impaired Arousal from Sleep (Sleep Inertia)
treatment_effect: INHIBITS
description: >-
Reduces sleep inertia in randomised withdrawal, distinguishing it from the
wake-promoting agents, which do not address this node.
- target: Increased Homeostatic Sleep Drive with Preserved Sleep Continuity
treatment_effect: INHIBITS
description: >-
Reduces daytime sleepiness alongside the effect on sleep inertia.
evidence:
- reference: PMID:36921459
reference_title: "Update on the treatment of idiopathic hypersomnia: Progress, challenges, and expert opinion."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In a placebo-controlled, double-blind, randomized withdrawal study, LXB
reduced daytime sleepiness and sleep inertia, and improved daily
functioning.
explanation: >-
Randomised-withdrawal evidence that the agent acts on both curated
symptom nodes, which is what distinguishes it from the wake-promoting
agents.
- reference: PMID:37409509
reference_title: "Long-term efficacy and safety of low-sodium oxybate in an open-label extension period of a placebo-controlled, double-blind, randomized withdrawal study in adults with idiopathic hypersomnia."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Efficacy and safety of low-sodium oxybate were maintained or improved
during the 6-month OLE, supporting long-term treatment with low-sodium
oxybate in adults with idiopathic hypersomnia.
explanation: >-
Cited as PARTIAL because the durability claim comes from an open-label
extension without a control arm, so it supports persistence of benefit
more weakly than the randomised-withdrawal result above.
clinical_trials:
- name: NCT03533114
phase: PHASE_III
status: COMPLETED
description: >-
Double-blind, placebo-controlled, randomised-withdrawal study of low-sodium
oxybate (JZP-258) in idiopathic hypersomnia with an open-label safety
extension; the trial supporting the 2021 United States approval.
target_phenotypes:
- preferred_term: Excessive daytime somnolence
term:
id: HP:0001262
label: Excessive daytime somnolence
- preferred_term: Sleep drunkenness
term:
id: HP:6000456
label: Sleep drunkeness
evidence:
- reference: PMID:37409509
reference_title: "Long-term efficacy and safety of low-sodium oxybate in an open-label extension period of a placebo-controlled, double-blind, randomized withdrawal study in adults with idiopathic hypersomnia."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
To evaluate 6-month efficacy and safety of low-sodium oxybate in people
with idiopathic hypersomnia during an open-label extension period (OLE) of
a phase 3 clinical trial.
explanation: >-
Identifies the phase 3 trial and its open-label extension, the source of
the efficacy evidence curated under treatments.
prevalence:
- population: Wisconsin Sleep Cohort, working-age adults with polysomnography and MSLT data
measure_type: POINT_PREVALENCE
prevalence_class: ABOVE_1_IN_1000
rate_per_100000: 1500.0
rate_low: 700.0
rate_high: 2500.0
notes: >-
The first population-based estimate; 12 probable cases among 792 participants
with objective sleep testing. Substantially higher than clinic-derived
impressions of the disorder's rarity, and the authors note this explicitly.
Read with care - "probable IH" was ascertained by applying criteria to an
existing cohort rather than by clinical diagnosis, so this is a prevalence of
the phenotype meeting criteria rather than of the diagnosed disease.
evidence:
- reference: PMID:38165322
reference_title: Prevalence and Course of Idiopathic Hypersomnia in the Wisconsin Sleep Cohort Study.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
From 792 cohort study participants with available polysomnography and
multiple sleep latency test data, 12 cases with probable IH were identified
resulting in an estimated prevalence of IH of 1.5%
explanation: >-
Gives the numerator, denominator, and resulting rate directly.
- reference: PMID:38165322
reference_title: Prevalence and Course of Idiopathic Hypersomnia in the Wisconsin Sleep Cohort Study.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
These results demonstrate IH is more common in the working population than
generally assumed
explanation: >-
Records the authors' own framing of the estimate against prior
assumptions, which is why the note flags the ascertainment caveat.
classifications:
harrisons_chapter:
- classification_value: NEUROLOGIC
evidence:
- reference: PMID:36921459
reference_title: "Update on the treatment of idiopathic hypersomnia: Progress, challenges, and expert opinion."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Idiopathic hypersomnia is a central hypersomnolence disorder of unknown
origin
explanation: >-
A central (i.e. central nervous system) disorder of hypersomnolence,
classified under the nervous-system chapter as the closest available
category; the schema has no dedicated sleep chapter.
discussions:
- discussion_id: gap_ih_versus_narcolepsy_type_2_entity_validity
kind: KNOWLEDGE_GAP
prompt: >-
Are idiopathic hypersomnia and narcolepsy type 2 one disorder or two?
attaches_to:
- pathophysiology#Unidentified Somnogenic Process
rationale: >-
The two diagnoses are separated by a single polysomnographic count - two or
more sleep-onset REM periods on the multiple sleep latency test - applied to
a test its own reviewers describe as neither sensitive nor specific, and the
count is unstable on repeat testing. Neither disorder has a biological
marker, both have normal CSF hypocretin-1, and they respond to the same
drugs. This is not a nosological quibble: it determines whether mechanistic
studies of either are being conducted in a homogeneous population, and a
negative replication in a mixed cohort would be uninterpretable. It is the
principal reason this entry's trigger node is curated as unknown rather than
inheriting a mechanism from narcolepsy research.
proposed_experiments:
- experiment_id: exp_repeat_mslt_classification_stability
name: Stability of the SOREMP-based classification on repeat testing
description: >-
Serial multiple sleep latency testing at intervals in a cohort meeting
criteria for either diagnosis, quantifying how often patients cross the
two-SOREMP boundary between tests, and testing whether any clinical,
biochemical, or genetic variable segregates with the assigned label
independently of that count.
- discussion_id: gap_gaba_potentiation_replication
kind: KNOWLEDGE_GAP
prompt: >-
Has the CSF GABA-A-potentiating bioactivity been independently replicated,
and what is the substance?
attaches_to:
- pathophysiology#Impaired Arousal from Sleep (Sleep Inertia)
rationale: >-
The gabaergic_potentiation hypothesis is the only mechanistic account of
idiopathic hypersomnia with direct experimental support, and it is curated
here as EMERGING rather than canonical for two specific reasons that are
resolvable rather than permanent. The bioactive substance was characterised
only as a trypsin-sensitive species of 500-3000 daltons and has never been
identified, so there is no assay a second laboratory can run on the analyte
itself; and the supporting clinical observation was open-label in seven
patients. Until both are addressed, a conforming or citing entry should not
treat GABA-A potentiation as established.
proposed_experiments:
- experiment_id: exp_csf_somnogen_identification
name: Molecular identification of the CSF bioactivity
description: >-
Fractionation and mass-spectrometric identification of the
GABA-A-potentiating component of hypersomnolent CSF, followed by a blinded
multi-site assay of the identified analyte in patients meeting criteria for
idiopathic hypersomnia, narcolepsy type 2, and matched controls.
- experiment_id: exp_flumazenil_randomised_trial
name: Randomised placebo-controlled trial of flumazenil
description: >-
A blinded, placebo-controlled crossover trial of flumazenil in
hypersomnolent patients selected by CSF bioactivity status, with objective
vigilance and sleep-inertia endpoints, to test whether the open-label
response survives control and whether it segregates with the biomarker.