Definition and Diagnosis
Narcolepsy is a chronic disorder of the sleep-wake cycle characterized by recurrent, irrepressible episodes of daytime sleepiness and, in many cases, cataplexy (sudden, brief loss of muscle tone triggered by strong emotion), reflecting dysregulation of REM sleep intrusion into wakefulness.
Epidemiology
Narcolepsy is relatively rare, affecting an estimated 0.02-0.05% of the population, with onset typically in adolescence or young adulthood, and type 1 (with cataplexy) linked to loss of hypocretin/orexin-producing neurons.
Risk Factors
Risk factors include genetic predisposition (strong association with the HLA-DQB1*06:02 allele), autoimmune processes affecting hypocretin-producing neurons, and, in some cases, a preceding infection or immunization has been implicated as a trigger.
Symptoms and Subtypes
Core features include excessive daytime sleepiness with irresistible sleep episodes, cataplexy (in type 1), sleep paralysis, hypnagogic or hypnopompic hallucinations, and fragmented nighttime sleep.
Diagnosis
Diagnosis involves clinical history, polysomnography followed by a multiple sleep latency test showing short sleep latency and early-onset REM periods, and, when available, measurement of cerebrospinal fluid hypocretin levels.
Treatment
Treatment includes scheduled daytime naps, stimulant medications (such as modafinil or amphetamine-type stimulants) for sleepiness, and sodium oxybate or antidepressants for cataplexy, tailored to symptom severity and type.
Prognosis
Narcolepsy is a lifelong condition, but with appropriate pharmacological and behavioral management, most individuals can achieve meaningful improvement in daytime functioning and safety.
Reference
New Oxford Textbook of Psychiatry (2nd ed.).