Multiple sclerosis and narcolepsy/cataplexy in a monozygotic twin.

Symptoms of narcolepsy/cataplexy developed in a monozygotic twin at the age of 56 years, 25 years after the onset of multiple sclerosis. The diagnosis of narcolepsy/cataplexy was confirmed by polygraphic recordings demonstrating sleep-onset periods of rapid eye movements (REM), increase in REM time per 24 hours, and disturbed nocturnal sleep. Frequent catapletic attacks were almost completely controlled by clomipramine. These symptoms may constitute one of the paroxysmal syndromes in multiple sclerosis. The discordancy for multiple sclerosis is attributed to a submaximal risk factor in the HLA system and a strong environmental factor in only one of the twins.