Narcolepsy

Nadav Traeger, MD, FAAP, FCCP, DABSM

Introduction

•Narcolepsy is felt to be an intrusion of rapid eye movement (REM) sleep into wakefulness. The body is relatively atonic during REM sleep, which is when dreams occur. Thus, narcolepsy is characterized by excessive daytime sleepiness and symptoms of REM-sleep dissociation.

•The 2 diagnostic subtypes are

—Narcolepsy type 1 (narcolepsy with cataplexy)

—Narcolepsy type 2 (narcolepsy without cataplexy)

Etiology

•Narcolepsy type 1 is caused by a deficiency in central nervous system hypocretin (also known as orexin) levels, most likely caused by a selective loss of hypothalamic hypocretin-producing neurons. Patients with sleepiness and low or absent cerebrospinal fluid (CSF) hypocretin levels are classified as having narcolepsy type 1, even if they do not yet manifest cataplexy.

—A strong association with certain human leukocyte antigen (HLA) subtypes (DR2/DRB1*1501, DQB1*0602, DQB1*0602) suggests the involvement of autoimmune destruction of the hypocretin- releasing brain regions.

—The specific triggering event is unknown, with varying lines of evidence implicating various environmental factors, such as trauma or infections (including β-hemolytic Streptococcus and viruses, such as influenza), and, in rare instances, also physical damage resulting from strokes, trauma, tumors, and neurological disease.

•The genetic and environmental factors associated with narcolepsy type 2 are unknown.

Epidemiology

•Narcolepsy in childhood is underrecognized and underdiagnosed, often being mistaken for behavioral or mood disorders.

•Narcolepsy type 1 occurs in 0.02%–0.18% of people in the United States.

•The prevalence of narcolepsy type 2 is more uncertain and is thought to represent a minority (about 15%–25%) of the total narcoleptic population.

•Both sexes are affected, with a slight preponderance of male sex.

Specific for Narcolepsy

•Excessive daytime sleepiness

—This is the most common symptom and often the most debilitating.

—The patient experiences repeated daily episodes of unintentional lapses into sleep.

—Unlike patients with other sleep disorders (eg, obstructive sleep apnea syndrome [OSAS]), patients with narcolepsy typically wake up feeling refreshed after a full night’s sleep or a brief nap but then begin to feel sleepy again after variable times (perhaps 1–2 hours), especially when sedentary.