Narcolepsy is present in 0.05 per cent of the population and usually starts in the second or third decade of life. Sufferers present with excessive sleepiness and can have periods of sleep with little or no warning of sleep onset. Other symptoms include cataplexy, sleep paralysis and vivid hypnagogic hallucinations. The majority of sufferers are HLA-DR2 positive. There is a subgroup of individuals who are excessively sleepy but do not have all the diagnostic features of narcolepsy. Inadequate warning of oncoming sleep and cataplexy put drivers at high risk.
Diagnosis of narcolepsy is made on the combination of clinical features. HLA typing and a multiple sleep latency test (MSLT), with a diagnostic sleep study on the prior night to exclude other sleep disorders and aid interpretation of the MSLT.14
Persons suspected of having narcolepsy should be referred to a sleep specialist or neurologist for assessment (including a MSLT) and management.
Sleepiness in narcolepsy can usually be managed effectively with scheduled naps and stimulant medication. Tricyclic antidepressants and monoamine oxidase (MAO) inhibitors are used to treat cataplexy. Commercial vehicle drivers on a conditional licence should have a review at least annually by their specialist.