Fig. 1. Proposed diagnostic workup for central disorders of hypersomnolence.

The diagram shows the hierarchy of clinical reasoning and investigations that may be done to arrive at a diagnosis of one of the central hypersomnolence disorders. The occurrence of typical cataplexy is at the top of the hierarchy: its presence indicates a diagnosis of narcolepsy type 1, even with comorbid sleep apnea or chronic sleep deprivation. Absent typical cataplexy, two phenotypes are possible: inability to stay awake during the day with no increased amount of daytime sleep (excessive daytime sleepiness, EDS, left column), or an increased amount of sleep and, despite that, complaints of excessive daytime sleepiness (excessive need for sleep, ENS, right column). In these situations, chronic sleep deprivation must first be ruled out as the cause, then obstructive sleep apnea (OSA, if hypersomnolence disappears after OSA treatment) and other neurological and psychiatric diseases. If these alternatives are ruled out and diagnostic criteria are fulfilled, the diagnoses of narcolepsy type 2 or idiopathic hypersomnia may be considered. PSG, polysomnography, possibly performed for 24 h. MSLT, multiple sleep latency test.