Fragmentary pathological myoclonus in NREM sleep.

A 42-year-old patient is reported who presented with marked daytime sleepiness and in whom the only major nocturnal polysomnographic abnormality was intense fragmentary (partial) myoclonus occurring with equal frequency in all stages of NREM sleep associated with some degree of sleep fragmentation. The myoclonus was very brief (less than 150 msec duration), aperiodic and recurred in asynchronous and asymmetrical fashion over the legs, arms and face. It appears unrelated to the clinically similar physiological myoclonus of REM sleep. Other main sleep disorders such as periodic movements, restless leg syndrome, sleep apnea and narcolepsy-cataplexy were excluded by history and polysomnography.