Abstract
"Muscle activity in the legs (MAL)" extends the classification, nocturnal myoclonus (NM), to include all phasic muscle activity in the legs during sleep, irrespective of the repetitiveness, periodicity, or minimum duration of the muscle events. This study examined MAL and MAL-associated arousals and awakenings in narcoleptics, obstructive sleep apnea (OSA) patients, NM patients, and normals. Clinical scoring of patients' polysomnograms indicated that narcoleptics and NM patients had significantly more MAL arousals/hr and MAL awakenings/hr than OSA patients. Narcoleptics had significantly more MAL awakenings/hr than NM patients as well as more MAL arousals/hr than NM patients, but this was not significant. There were no significant between-group differences for MAL events without arousal.MAL events were rated as isolated or in series of (GREATERTHEQ)4 events, short ((LESSTHEQ)0.5 sec) or long ((GREATERTHEQ)0.5 sec), in non-REM or REM sleep, and by the degree of arousal following each MAL event in the polysomnograms of nine randomly selected individuals from each patient group, and nine asymptomatic controls. As in the clinical scoring, narcoleptics had significantly more MAL arousals/hr and awakenings/hr than controls and OSA patients, and significantly more MAL awakenings/hr than NM patients. NM patients had significantly more MAL arousals/hr and MAL awakenings/hr than controls and OSA patients, using log-transformed data. Only long MAL within a series fulfills standard criteria for NM events, but many MAL arousals (24%) and MAL awakenings (38%) followed MAL that was not long and part of a series. Therefore, the criteria for leg muscle events in NM may need to be broadened.Only 12.7% of MAL occurrences were followed by arousals or awakenings, and MAL arousals and awakenings accounted for fewer than one-fourth of the arousals and awakenings in narcoleptics and NM patients. Furthermore, there were no significant differences between sleep stages in NM patients versus controls; however, most control subjects snored, which can cause frequent arousals. Although MAL may be the primary pathological factor for many NM patients, these findings suggest that factors other than MAL arousals and MAL awakenings also contribute to the sleep complaints of some NM patients.