Narcolepsy is a disorder of impaired expression of wakefulness and rapid-eye-movement (REM) sleep. This manifests as
excessive daytime sleepiness and expression of individual physiological correlates of REM sleep that include
cataplexy and
sleep paralysis (REM sleep atonia intruding into wakefulness), impaired maintenance of REM sleep atonia (e.g. REM sleep behaviour disorder [RBD]), and dream imagery intruding into wakefulness (e.g. hypnagogic and hypnopompic
hallucinations). Excessive
sleepiness typically begins in the second or third decade followed by expression of auxiliary symptoms. Only
cataplexy exhibits a high specificity for diagnosis of
narcolepsy. While the natural history is poorly defined,
narcolepsy appears to be lifelong but not progressive. Mild disease severity, misdiagnoses or long delays in
cataplexy expression often cause long intervals between symptom onset, presentation and diagnosis. Only 15-30% of narcoleptic individuals are ever diagnosed or treated, and nearly half first present for diagnosis after the age of 40 years. Attention to periodic leg movements (PLM), sleep apnoea and RBD is particularly important in the management of the older narcoleptic patient, in whom these conditions are more likely to occur. Diagnosis requires nocturnal polysomnography (NPSG) followed by multiple sleep latency testing (MSLT). The NPSG of a narcoleptic patient may be totally normal, or demonstrate the patient has a short nocturnal REM sleep latency, exhibits unexplained arousals or PLM. The MSLT diagnostic criteria for
narcolepsy include short sleep latencies (<8 minutes) and at least two
naps with sleep-onset REM sleep. Treatment includes counselling as to the chronic nature of
narcolepsy, the potential for developing further symptoms reflective of REM sleep dyscontrol, and the hazards associated with driving and operating machinery. Elderly narcoleptic patients, despite age-related decrements in sleep quality, are generally less sleepy and less likely to evidence REM sleep dyscontrol. Nonpharmacological management also includes maintenance of a strict wake-sleep schedule, good sleep hygiene, the benefits of afternoon
naps and a programme of regular exercise. Thereafter, treatment is highly individualised, depending on the severity of
daytime sleepiness,
cataplexy and sleep disruption.
Wake-promoting agents include the traditional psychostimulants. More recently, treatment with the 'activating'
antidepressants and the novel wake-promoting agent
modafinil has been advocated.
Cataplexy is especially responsive to
antidepressants which enhance synaptic levels of
noradrenaline (
norepinephrine) and/or
serotonin. Obstructive sleep apnoea and PLMs are more common in
narcolepsy and should be suspected when previously well controlled older
narcolepsy patients exhibit a worsening of symptoms. The discovery that
narcolepsy/
cataplexy results from the absence of neuroexcitatory properties of the hypothalamic
hypocretin-peptidergic system will significantly advance understanding and treatment of the symptom complex in the future.