How is Narcolepsy Diagnosed

Michael J. Thorpy, MD, ChB, Director of the Sleep-Wake Disorders Center at the Montefiore Medical Center, discusses how narcolepsy is typically diagnosed.

As Dr. Thorpy explains, narcolepsy is a rare neurological disorder characterized by excessive sleepiness during the day, often with periods of brief involuntary sleep and/or cataplexy. There are two subtypes of narcolepsy: type 1 narcolepsy in which the patient experiences episodes of cataplexy and type 2 narcolepsy in which a patient does not experience cataplexy.

Narcolepsy may be preliminarily diagnosed based on excessive daytime sleepiness, abnormal REM sleep phenomena (such as cataplexy), and/or disturbed nocturnal sleep. However, formal diagnosis requires an in-depth sleep analysis by sleep specialists. One measure is a polysomnographic evaluation of a patient’s nighttime sleep and daytime sleepiness. Alternatively, a physician can measure a patient’s cerebrospinal fluid hypocretin-1 level, though this measurement has been primarily used as a research tool rather than a clinical one and is often avoided due to the pain, discomfort, and potential comorbidities caused by spinal taps. Nevertheless, this measure can be helpful in cases where it is unclear based on sleep study results alone whether a patient has narcolepsy.