Emmanuel Mignot, the Stanford researcher who co-discovered orexin and its role in narcolepsy, argues in a new review that the standard diagnostic test for hypersomnia, the Multiple Sleep Latency Test (MSLT), has a high false-positive rate outside of narcolepsy type 1 and proposes returning to four historically grounded clinical subtypes to guide diagnosis and treatment.
What he proposes
Writing in L’Encephale, Mignot argues that excessive daytime sleepiness is routinely misattributed. Mild obstructive sleep apnea (OSA) is overtreated for sleepiness when depression, insufficient sleep, or shift work are the real drivers. The MSLT, the gold-standard nap test, performs well only for confirming narcolepsy type 1 (NT1), the form with cataplexy and orexin deficiency. For narcolepsy type 2 and idiopathic hypersomnia, the false-positive rate is problematic, leading to questionable diagnoses.
He proposes four clinical subtypes:
1. Narcolepsy Type 1, Cataplexy, refreshing naps, sleep-onset REM periods. Caused by orexin deficiency. Responds to oxybate, antidepressants, stimulants, and low-dose orexin receptor 2 agonists (in development).
2. Narcolepsy-like Hypersomnolence, Irresistible sleep attacks with short, refreshing naps. Insufficient sleep syndrome must be excluded. Often responds to modafinil.
3. Idiopathic Hypersomnia with Sleep Inertia, Excessive sleep amounts, severe sleep inertia, long unrefreshing naps. Frequently associated with psychiatric comorbidities, notably resolved depression. Sodium oxybate can be transformative.
4. Kleine-Levin Syndrome, Periodic extreme hypersomnia with apathy and derealization. Responds to lithium in roughly 50% of cases. Mignot notes a likely pathophysiological overlap with bipolar disorder.
Why it matters
This is not just academic classification. Mignot is arguably the most influential figure in modern narcolepsy research, his lab discovered the link between orexin (hypocretin) loss and narcolepsy in 1999, transforming it from a puzzling sleep disorder into a well-understood neurodegenerative condition. His call to revisit how hypersomnia is diagnosed carries weight.
The practical implications are significant. If the MSLT is overdiagnosing narcolepsy type 2 and idiopathic hypersomnia, patients may receive inappropriate treatment while the real cause, psychiatric illness, insufficient sleep, or another condition, goes unaddressed. Mignot’s proposed framework ties each subtype to specific treatment responses, from modafinil for narcolepsy-like hypersomnolence to oxybate for idiopathic hypersomnia with sleep inertia.
The review also highlights an emerging therapeutic frontier: orexin receptor agonists, now in clinical development, could become the first targeted pharmacotherapy for hypersomnia. Greater collaboration between psychiatry and sleep medicine will be essential as these treatments become available.
Limits
This is a perspective piece reflecting Mignot’s clinical experience and interpretation of the literature, not a systematic review. The proposed four-subtype framework has not been prospectively validated. The MSLT criticism is based on known false-positive rates; alternative diagnostic approaches are suggested but not yet standardized.
Bottom line
Excessive daytime sleepiness is routinely misdiagnosed, and the standard nap test may be overdiagnosing certain hypersomnia subtypes. Mignot proposes a return to four clinically defined categories, NT1, narcolepsy-like hypersomnolence, idiopathic hypersomnia with sleep inertia, and Kleine-Levin syndrome, each with distinct treatment pathways and stronger ties to psychiatric comorbidity than current diagnostic frameworks acknowledge.
Source
Mignot E. Redefining hypersomnia disorders in the context of psychiatry. L’Encephale. 2026;52(3S):S94-S99. doi:10.1016/j.encep.2026.04.001. PMID: 42297543.