Narcolepsy is characterised by the classic tetrad of excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, and sleep paralysis. Note that this tetrad is seen only rarely in children. The term “narcolepsy” is derived from Greek, “seized by somnolence.” Gelineau was the first to delineate the syndrome in 1880.
Narcolepsy frequently is unrecognised, with a typical delay of 10 years between onset and diagnosis. Approximately 50% of adults with the disorder retrospectively report symptoms beginning in their teenage years. This disorder may lead to impairment of social and academic performance in otherwise intellectually normal children. The implications of the disease are often misunderstood by patients, parents, teachers, and health care professionals.
Narcolepsy is treatable. However, a multimodal approach is required for the most favourable outcome.
Narcolepsy is thought to result from genetic predisposition, abnormal neurotransmitter functioning and sensitivity, and abnormal immune modulation. Current data implicate certain human leukocyte antigen (HLA) subtypes and abnormalities in monoamine synaptic transmission, particularly in the pontine reticular activating system.
Understanding of the neurochemistry of narcolepsy stems primarily from research involving narcoleptic dogs (eg, special laboratory-bred Dobermans and Labradors ). In these animal models, the disorder is transmitted in an autosomal recessive fashion with full penetrance and is characterised mainly by cataplexy.Excessive daytime sleepiness (EDS) is the primary symptom of narcolepsy.
- Sleepiness is a normal experience that cycles and invariably occurs after prolonged wakefulness. In healthy persons, mild sleepiness is apparent only during boring situations (eg, falling asleep while watching TV).
- In patients with narcolepsy, severe EDS leads to involuntary somnolence during more active conditions such as eating and talking. Sleepiness in narcolepsy may be severe and constant, with paroxysms during which patients may fall asleep without warning (ie, sleep attacks).
- Patients with narcolepsy tend to take short and refreshing naps (ie, REM type naps) during the day.
- Several questionnaires evaluate sleepiness. The most commonly used is the 8-question Epworth Sleepiness Scale (1991).
- Patients respond to each question on a scale from 0 (not at all likely to fall asleep) to 3 (very likely to fall asleep).
- The resulting total score is between 0 and 24.
- Although what score constitutes abnormal sleepiness is controversial, total scores above 10 generally warrant investigation.
Cataplexy (Latin, “to strike down with fear”) is an abrupt attack of muscle weakness.
- If severe and generalised, it may cause a fall.
- More subtle forms exist with only partial loss of tone (eg, head nod).
- The most characteristic feature of cataplexy is that it usually is triggered by emotions (usually laughter and anger).
- Cataplexy is seen in about 70% of patients with narcolepsy, and its presence with EDS strongly suggests the diagnosis of narcolepsy.
- Specific historical questions concerning cataplexy are required.
Sleep paralysis is the inability to move upon falling asleep or awakening with consciousness intact.
- It often is accompanied by hallucinations.
- Sleep paralysis occurs during REM sleep in healthy subjects.
- Sleep-related hallucinations may occur at sleep onset (ie, hypnagogic) or awakening (ie, hypnopompic) and are usually vivid (dreamlike) visual, auditory, or tactile in nature.
The classic picture of narcolepsy may be somewhat different in young children.
- Children may deny EDS because of embarrassment.
- Sometimes restlessness and motor over activity may predominate.
- Academic deterioration, inattentiveness, and emotional lability are common.
In one study of 51 prepubertal patients with narcolepsy, the following initial complaints were noted:
- Children younger than 5 years presented with unexplained falls and “drop attacks,” aggressive behaviour, abrupt irritability, sleep terrors, and abrupt dropping of objects.
- In children aged 5-10 years, the most common initial complaint was repetitive sleepiness, followed by difficulty with morning arousal associated with aggressive behaviour and abrupt falls in school. These children often were misdiagnosed as having attention deficit hyperactivity disorder (ADHD), learning disability, or another neurologic disorder.
- In children aged 10-12 years, poor academic performance was a common complaint. Other presenting symptoms included inappropriate low level of alertness, falling asleep in class, and inability to wake up in the morning.