Redefining hypersomnia disorders in the context of psychiatry

Daytime sleepiness and excessive sleep are frequent symptoms. When these symptoms are recognized, they are often attributed to comorbid depression or, following ambulatory screening, to obstructive sleep apnea (OSA). While OSA affects 20-50% of the population, more frequently in men, its contribution to sleepiness in the general population is modest, and subjective sleepiness shows stronger associations with depression, insufficient sleep, and shift work. As a result, mild OSA in the presence of sleepiness is often overtreated. Further, stimulants are used as adjunct therapy in depression despite limited evidence. When referred to sleep disorder specialists, after exclusion of OSA, these patients are typically evaluated using a daytime nap test, the Multiple Sleep Latency Test (MSLT). The MSLT is used to diagnose Narcolepsy or Idiopathic Hypersomnia. Problematically, the MSLT performs well only to confirm narcolepsy type 1, a disorder with cataplexy and caused by orexin deficiency. A high false positive rate occurs in the absence of cataplexy, leading to questionable diagnoses of narcolepsy type 2 and idiopathic hypersomnia. A return to four historical subtypes of central nervous system hypersomnolence independent of MSLT testing is proposed. Narcolepsy Type 1: cataplexy, refreshing naps, sleep-onset REM periods. It is caused by orexin deficiency, responds to oxybate, antidepressants, stimulants, and low dose orexin receptor 2 agonists (in development). Narcolepsy-like hypersomnolence: Irresistible sleep attacks with short, refreshing naps. Insufficient Sleep must be excluded. It is often responsive to modafinil. Idiopathic Hypersomnia with sleep inertia and unrefreshing sleep: Excessive sleep amounts, severe sleep inertia, and long, unrefreshing naps. Association with psychiatric comorbidities, notably resolved depression, is frequent. Sodium oxybate can be transformative. Kleine-Levin Syndrome: periodic extreme hypersomnia with apathy and derealization. Responds to lithium in ∼50% of cases. A pathophysiological overlap with bipolar disorder is likely. A greater collaboration between psychiatry and sleep medicine is needed considering the emergence of orexin receptor agonists as potential therapies for hypersomnia.