[A case of spinal segmental myoclonus and propriospinal myoclonus: a neuroelectrophysiologic analysis]

A 37-year-old male patient with spinal segmental myoclonus and propriospinal myoclonus was described. He was admitted to our hospital because of paroxysmal axial myoclonus, which first appeared one month before. He denied any significant accident such as trauma or fever. Apart from myoclonus, no abnormal findings were observed by physical and neurological examinations, routine laboratory investigations and MRI of the cervical and thoracic spinal cords. The myoclonus consisted of continuous rhythmic contractions of the bilateral thoracal and abdominal muscles. Its frequency was approximately 0.3Hz. The clinical findings were typical of spinal segmental myoclonus. In addition, the myoclonus started in the thoracal muscles and frequently spread up to the neck muscles and down to the leg muscles. The myoclonus disappeared in sleep. Polymyography revealed the following findings: (1) The jerks were found on the bilateral axial muscles including sternocleidomastoid, biceps, triceps, pectoralis major, abdominal muscles and quadriceps. (2) Homologous muscles were activated synchronously. (3) The duration of bursts was variable ranging 100 to 400msec. (4) The jerks in the pectoralis muscle preceded those in other muscles. The latencies of the jerks in the other muscles increased with their distance from pectoralis, based on the linear regression analysis of the onset of jerks in the various muscles. (5) The jerks were induced by tapping or electrical stimulation anywhere on the body including the face, but not by flash or sound. From the above polymyographical findings, the myoclonus seems to originate in the T3 spinal cord and slowly up and down the spinal cord at 0.6-1.6 m/sec, suggesting that it is mediated by the propriospinal tract.