Narcolepsy is characterized by episodes of irrepressible sleep occurring during the daytime, often during monotonous activities. These episodes typically last 10–20 minutes and occur against a background of continuous sleepiness in most patients. Hypersomnia in narcolepsy is usually associated with one or more other symptoms, including cataplexy, hypnagogic hallucinations, and sleep paralysis, although these symptoms do not necessarily occur together.
Cataplexy is a sudden loss of muscle tone triggered by laughter or excitement, causing the patient to fall without losing consciousness. It must be distinguished from conditions such as epilepsy, hyperekplexia, Niemann–Pick C disease, and Coffin–Lowry syndrome. The full tetrad of narcolepsy symptoms occurs in only 10% of adult patients, with many children presenting behavior problems or learning difficulties due to sleepiness and efforts to stay awake.
Narcolepsy is a rare condition with an incidence of 0.03% in both adult and pediatric populations. Many adults with narcolepsy recall having symptoms since childhood, with about 80% of individuals experiencing onset before age 20 and up to 30% before age 15. The earliest recorded onset is in a 9-month-old child. The International Classification of Sleep Disorders (ICSD-3) recognizes two types of narcolepsy:
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Type 1 Narcolepsy: Associated with hypocretin deficiency, includes either cataplexy or reduced cerebrospinal fluid (CSF) hypocretin-1 levels. The deficiency in hypocretin-1 (orexin) peptides released from the dorsolateral hypothalamus is likely due to autoimmune destruction of hypocretin cells.
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Type 2 Narcolepsy: Characterized by normal CSF hypocretin-1 levels and polysomnographic evidence of a mean sleep latency of 8 minutes or less, plus at least two sleep onset rapid eye movement periods during multiple sleep latency tests and night polysomnography.
Approximately 98% of narcolepsy-cataplexy patients have human leukocyte antigen (HLA)-DR2 groups, especially DQB1-0602. An extremely small number of patients do not belong to these HLA groups. The gene(s) for narcolepsy may act through an autoimmune mechanism, resulting in the loss of orexin/hypocretin neurons due to environmental stress such as infections or H1N1 vaccines. There was a five-fold increase in narcolepsy incidence in pediatric and adult populations post-H1N1 vaccination.
Narcolepsy due to acquired brain injury, such as hypothalamic or pontomedullary lesions, can induce coma, permanent hypersomnia, or sleepiness. Narcolepsy proper refers to brief episodes of sleep occurring three to five times daily on average, with half the patients easy to awaken during an attack, and most children feeling unrefreshed afterward.
Cataplexy is defined as more than one episode of generally brief (less than 2 minutes), usually bilaterally symmetrical sudden loss of muscle tone with retained consciousness. The episodes are often triggered by strong emotions, usually positive ones. In children, cataplexy may present close to disease onset as facial (or generalized) hypotonia, with droopy eyelids, mouth opening, and protruded tongue or gait unsteadiness.
Hypnagogic hallucinations and sleep paralysis are less common, found in 40% and 30% of patients, respectively. Sleep paralysis consists of generalized hypotonia during the transition between sleep and wakefulness. In young children, day naps are often long (20–120 minutes) and unrefreshing.
Episodes of amnesic automatism simulating epilepsy occur in 8% of patients. Sleep paralysis, cataplexy, and hypnagogic hallucinations may reflect motor manifestations of REM sleep, which can occur in slight chronological dissociation from the behavioral component of sleep in narcoleptic individuals.
Hypocretin is involved in sleep regulation and several behaviors and neuroendocrine actions, including modulation of feeding behavior and energy balance. Accordingly, body weight or body mass index is frequently increased in patients with narcolepsy. Obesity is reported in 30% of adults with narcolepsy and at least 50% of children with narcolepsy, particularly the youngest ones. The high incidence of precocious puberty, obesity, and central hypothyroidism in children with narcolepsy could reflect broad hypothalamic abnormalities.
Narcolepsy is a lifelong condition that is often psychologically distressing. A good sleep regimen is essential for therapy, including a regular night sleep schedule, avoidance of long naps, and provision of short day rest periods. Treatment options include modafinil, which is effective for excessive daytime sleepiness, methylphenidate, and amphetamines, which may help some patients but have transitory effects. Antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) or imipramine, can benefit cataplexy, and sodium oxybate can reduce cataplexy frequency, excessive daytime sleepiness, and dyssomnia. New therapies, such as the inverse agonist of the histamine H3 receptor, appear promising.
Making the correct diagnosis, offering reassurance that the disorder is not psychiatric, multidisciplinary follow-up, and academic support are crucial. Isolated cataplexy has been reported in patients with pontomedullary lesions, Coffin–Lowry syndrome, Niemann–Pick C disease, and Norrie syndrome, where it may account for previously reported atonic episodes.
References
Aicardi, J., & Ouvrier, R. (2018). Aicardi’s Diseases of the Nervous System in Childhood (4th ed.). Mac Keith Press.
