Muscle Activity in the Legs (MAL) Associated with Frequent Arousals in Narcoleptics,Nocturnal Myoclonus and Obstructive Sleep Apnea (OSA) Patients

“Muscle activity in the legs (MAL)” is an extension of the classification, nocturnal myoclonus, to include all phasic muscle activity in the legs during sleep, irrespective of the repetitiveness, periodicity, or minimum duration of the muscle events. This report examined the number of MAL events and, especially, MAL events associated with arousals (MAL arousals) and awakenings (MAL awakenings) in the clinical records of 9 narcoleptics, 42 obstructive sleep apnea (OSA) patients, and 12 nocturnal myoclonus patients. The mean MAL arousals/hr for narcoleptics, OSA patients, and nocturnal myoclonus patients were 20.5, 3.0, and 12.9, respectively; the mean MAL awakenings/hr were 2.5, 0.2, and 1.3, respectively. Both the narcoleptics and nocturnal myoclonus patients had significantly more MAL arousals/hr and MAL awakenings/hr of sleep than OSA patients. Nonetheless, 62% of the OSA patients had ≥ 1 MAL arousal/hr. Narcoleptics had significantly more MAL awakenings/hr than nocturnal myoclonus patients; narcoleptics also had more MAL arousals/hr of sleep than nocturnal myoclonus patients, but this difference was not significant. Most, 89%, of the narcoleptics, 22% of the OSA patients, and 100% of the nocturnal myoclonus patients had ≥ 5 MAL arousals/hr of sleep. These findings suggest that there may be a relationship between the pathogenesis of MAL, narcolepsy, and OSA.