History
HISTORY OF IDIOPATHIC-HYPERSOMNIA (IH)
The history of idiopathic hypersomnia (IH) began with Bedrich Roth’s description of sleep drunkenness in 1956. In 1976, Roth officially coined the term “idiopathic hypersomnia,” defining it by two forms: polysymptomatic, characterized by long sleep duration, sleep drunkenness, unrefreshing naps, and excessive daytime sleepiness, and monosymptomatic, defined only by excessive daytime sleepiness.
Key developments in the understanding and classification of IH:
1979 The Diagnostic Classification of Sleep and Arousal Disorders used the term “idiopathic CNS hypersomnia,” merging the two forms of idiopathic hypersomnia and mentioning that symptoms such as total nocturnal sleep time of long duration or great difficulty in awakening affected many of the patients.
1990 The International Classification of Sleep Disorders (ICSD) reverted to the term IH, recognizing a single form of the disorder with variable symptoms. Polysomnographic criteria included a normal or prolonged sleep period, sleep latency less than 10 minutes, normal REM sleep latency, a Multiple Sleep Latency Test (MSLT) showing a sleep latency of less than 10 minutes, and fewer than two sleep-onset REM periods (SOREMPs) on the MSLT.
1997 Bassetti and Aldrich identified three clinical forms of IH: classic (non-overwhelming sleepiness, long unrefreshing naps, prolonged nighttime sleep, and difficulty awakening), narcoleptic-like (overwhelming hypersomnolence, short refreshing naps, and easy awakening), and mixed (features intermediate between the other two).
1998 Billiard et al. suggested returning to Roth’s initial distinction, replacing the terms polysymptomatic and monosymptomatic by the terms complete and incomplete and adding ICSD electrophysiological features.
2005 IH was separated into two subgroups: idiopathic hypersomnia with long sleep time (IHwLST) and idiopathic hypersomnia without long sleep time.
2021 The FDA approved Xywav, an oral solution of calcium, magnesium, potassium, and sodium oxybates, as a medication for IH.
Because of the complexities and rarity of IH, research is limited, and IH often goes undiagnosed.
Current Challenges in Diagnosing Idiopathic Hypersomnia
1. Lack of Reliable Objective Biomarkers
There are no established neurobiological markers for idiopathic hypersomnia (IH), so diagnosis relies heavily on self-reported symptoms and exclusion of other causes.
2. Limitations of Diagnostic Tests
The Multiple Sleep Latency Test (MSLT), a cornerstone of diagnosis, has limited sensitivity and reliability for IH. Up to half of people with IH may have normal results on standard sleep studies.
The MSLT can yield inconsistent results, and repeated testing may change a patient’s diagnosis between IH and narcolepsy type 2 (NT2).
Current protocols often do not capture total sleep time over 24 hours, which is important for distinguishing IH from other hypersomnias.
3. Symptom Overlap and Clinical Heterogeneity
IH symptoms overlap with those of NT2 and other sleep disorders, making differentiation challenging.
The disorder is rare and clinically heterogeneous, which can make recognition and diagnosis difficult even for experienced clinicians.
4. Exclusion of Other Conditions
Diagnosis requires meticulous exclusion of other causes of excessive daytime sleepiness, such as sleep deprivation, obstructive sleep apnea, circadian rhythm disorders, depression, and medication effects.
This process is time-consuming and often leads to significant diagnostic delays—sometimes up to 9 years.
5. Challenges with Current Diagnostic Criteria
The International Classification of Sleep Disorders (ICSD-3) criteria are seen as insufficiently nuanced, lacking ways to grade diagnostic certainty or measure long sleep time.
Some proposed improvements, such as multi-day/night sleep studies to measure extended sleep time, are logistically challenging and not widely available.
6. Impact of Medications and Comorbidities
Medications (especially those affecting REM sleep) and comorbid conditions can confound test results, requiring careful management before diagnostic testing.
7. Underrecognition and Delayed Diagnosis
IH is often underrecognized due to its rarity and overlap with more common sleep disorders, leading to delays in care and increased burden for patients.
Summary Table of Challenges
| Challenge | Description |
|---|---|
| Lack of biomarkers | No objective neurobiological markers for IH |
| Test limitations | MSLT/PSG have low sensitivity and reliability for IH |
| Symptom overlap | Difficult to distinguish from NT2 and other hypersomnias |
| Exclusion of other conditions | Requires ruling out many other causes of sleepiness |
| Diagnostic criteria limitations | ICSD-3 lacks nuance; long sleep time not easily measured |
| Medication/comorbidity confounding | Medications and comorbidities can alter test results |
| Underrecognition/delays | IH is rare and often misdiagnosed, leading to long delays in care |
In summary, diagnosing idiopathic hypersomnia remains challenging due to the absence of objective markers, unreliable and insensitive testing, symptom overlap with related disorders, and the need for comprehensive exclusion of other causes.
