[A case of propriospinal myoclonus at sleep onset in which video-polysomnography with additional surface electromyogram was useful for diagnosis]

Propriospinal myoclonus at sleep onset (PSM-S) is a sudden myoclonic jerk that occurs during the transition from wakefulness to sleep. It is a sleep-related movement disorder that causes difficulty falling asleep due to involuntary movements that spread caudally and rostrally through the propriospinal tract. Diagnosis requires observation of movements and polysomnography (PSG), and there are few reports. An 80-year-old man was referred to our center for insomnia due to abdominal movements at sleep onset. During the EEG test, we observed the caudal and rostral propagation of movements emanating from the abdomen. Attended video-PSG with additional surface electromyography revealed that myoclonic jerks occurred during the transition from wake to stage N1 and disappeared during sleep stage N2. EMG activity originated from the rectus abdominis muscle, followed by rostral and caudal propagation. Here, we report a case demonstrating that PSG with additional surface electromyography is important and useful for the diagnosis of PMS at sleep onset.