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Propriospinal myoclonus is one type of myoclonus that is proposed to originate in the spinal cord and spread up and down via propriospinal tract. There are a few reports describing the detailed electrophysiological findings of this myoclonus. In this communication, we present the results of electrophysiological analysis of a patient with propriospinal myoclonus. A 23-year-old woman suddenly noticed abdominal pain, which spontaneously faded in a few hours. Irregular involuntary flexion jerks of the trunk appeared spontaneously without pain or hiccups after this episode. It involved the bilateral axial muscles; sternocleidomastoid muscles (SCM), paravertebral muscles (PVM), abdominal muscles (ABD), and intercostal muscles (ICM), but not the limb muscles. It was worsened by the mental stress, but not by her posture or position. While she slept, the jerks were not observed. Routine laboratory examinations were all normal. Magnetic resonance imaging of the spinal cord revealed no abnormalities. The electrophysiological studies done on this patient are polymyography, back-averaging of the EEG activity preceding spontaneous jerks (jerk-locked averaging (JLA), and movement related cerebral potential (MRCP) preceding the involuntary jerks and voluntary abdominal movements. No EEG activities preceding the myoclonus were demonstrated by JLA or MRCP. No MRCP recorded preceding the myoclonus suggests that the jerk is not a self-initiated or externally triggered voluntary movement. Polymyography revealed that the jerks involved the bilateral axial muscles including SCM, PVM, ICM, and ABD, but not the limb muscles. Homologous muscles were activated synchronously. The duration of EMG bursts was variable ranging 50 to 250 ms in these muscles.(ABSTRACT TRUNCATED AT 250 WORDS)
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