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Differential Diagnosis of IH

Is it Idiopathic Hypersomnia (IH) or something else?

IH is a unique medical disorder that is different from other disorders, such as narcolepsy, sleep apnea, or depression1

Confidence in an IH diagnosis remains challenging for several reasons2:

  • Excessive daytime sleepiness () is a common symptom of many disorders
  • Ancillary symptoms overlap with other disorders
  • There is currently no validated biomarker for IH

The key symptoms of IH are often present in other sleep and/or mental disorders

Moderate EDS has been reported by3*:


of those with insomnia


of those with restless legs syndrome


of those with major depressive disorder


of those with obstructive sleep apnea


of those with anxiety disorders

*Based on a phone interview of 8937 adults in California, New York, and Texas. The questionnaire included questions on sleeping habits, life habits, health, DSM-IV mental disorders, and DSM-IV and ICSD sleep disorders. The prevalence of these disorders was significantly associated with moderate EDS (p<0.001) after adjusting for age, gender, and occupation.3

sleep inertia

is common with mental disorders1,4

  • In a study of nearly 600 people with unipolar depression, 74% of subjects reported having trouble getting out of bed4
  • People with IH have a prolonged and severe form of sleep inertia, and frequently use special devices or procedures to wake up1

Cognitive impairment or “Brain fog”

is common in various sleep-wake disorders5,6

  • Patients with narcolepsy type 1, insufficient sleep syndrome, and hypersomnia all show deficits in sustained vigilant attention6
  • It is unclear whether cognitive impairment is a nonspecific result of sleepiness or might be a disease-specific manifestation of IH5


is common with other sleep conditions1,7

  • While patients with narcolepsy generally find short naps to be restorative, patients with IH often find naps to be long (>1 hour) and unrefreshing1,7
  • Patients with IH usually do not benefit from prescribed or scheduled naps and try to avoid taking them7

prolonged sleep time

may be a sign of long-sleeper syndrome1

  • A long sleeper is an individual who consistently sleeps more per day than is typical for their age group8
  • Unlike patients with IH, long sleepers feel refreshed and do not have daytime sleepiness and difficulty awakening if they are allowed to sleep as long as they need1

Overlap of IH and narcolepsy symptoms can contribute to delayed diagnosis9*:


of patients with IH had multiple narcolepsy diagnoses before their first IH diagnosis

*These data are derived from a retrospective analysis of SHS (Symphony Healthcare Services) claims data that included 4544 patients with a narcolepsy diagnosis who had their first IH diagnosis within the considered period between 2014 to 2019. A 12-month look back from first IH diagnosis is considered to identify the number of narcolepsy diagnoses taken by IH patients; similarly, a 12-month look forward is applied after patient's second IH diagnosis to see the number of narcolepsy diagnoses taken by IH patients.9

Hypersomnolence may be caused by other medical disorders and illnesses including1,10:

  • Neurodegenerative diseases like Parkinson's disease and Alzheimer's disease
  • Genetic disorders like Prader-Willi syndrome and myotonic dystrophy
  • Viral pneumonia and Guillain-Barre syndrome, that can cause postviral hypersomnia within weeks or months following infection
Patients may go undiagnosed or misdiagnosed for as long as 10 to 15 years after the onset of initial symptoms11

Confident in your IH diagnosis?

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  1. American Academy of Sleep Medicine. International Classification of Sleep Disorders. 3rd ed. Darien, IL: American Academy of Sleep Medicine; 2014.
  2. Trotti LM. Idiopathic hypersomnia. Sleep Med Clin. 2017;12(3):331-344.
  3. Ohayon MM. Determining the level of sleepiness in the American population and its correlates. J Psychiatr Res. 2012;46(4):422-427.
  4. Trotti LM. Waking up is the hardest thing I do all day: sleep inertia and sleep drunkenness. Sleep Med Rev. 2017;35:76-84.
  5. Trotti LM, Arnulf I. Idiopathic hypersomnia and other hypersomnia syndromes. Neurotherapeutics. 2021;18(1):20-31.
  6. Thomann J et al. Psychomotor vigilance task demonstrates impaired vigilance in disorders with excessive daytime sleepiness. J Clin Sleep Med. 2014;10(9):1019-1024.
  7. Arnulf I, Leu-Semenescu S, Dodet P. Precision medicine for idiopathic hypersomnia. Sleep Med Clin. 2019;14(3):333-350.
  8. Billiard M, Sonka K. Idiopathic hypersomnia. Sleep Med Rev. 2016;29:23-33.
  9. Data on File (JZP258-2020-047). Jazz Pharmaceuticals, Inc.
  10. Dauvilliers Y. Differential diagnosis in hypersomnia. Curr Neurosci Rep. 2006;6(2):156-162.
  11. Masri TJ, Gonzales CG, Kushida CA. Idiopathic hypersomnia. Sleep Med Clin. 2012;283-289.

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