Propriospinal Myoclonus: Clinical and Neurophysiologic Characteristics

ABSTRACT

BACKGROUND: Propriospinal myoclonus (PSM) is characterized by rhythmic or arrhythmic, flexion or extension movements of the axial body muscles involving many spinal segments linked by long propriospinal pathways. We described the clinical and electrophysiological features of 7 PSM patients. METHODS: Neurophysiologic studies included routine electroencephalography, polymyography, and posterior tibial somatosensory evoked potentials (PTSEP). RESULTS: Myoclonic jerks originated from the rectus abdominis in 3 patients, and pectoralis major, thoracic paraspinalis, sternocleidomastoid, and vastus lateralis in every other case. Polymyography showed rostral and caudal propagations from the originated muscles. The durations of myoclonic jerks were about 100 to 400 ms and their velocities ranged from 3.2 to 6.7 (5.4+/-1.4) m/s. PSM developed after cervical trauma in 2 patients (cases 1, 2), after general anesthesia in case 4, and after infectious or inflammatory myelopathy in case 3. PSM in 3 patients were idiopathic, of which one patient had diabetes mellitus for 10 years with autonomic and somatosensory polyneuropathy. Two patients, who showed PSM after general anesthesia and myelopathy respectively, were cured completely within one month. Though others had not completely recovered, they had a relatively benign course. CONCLUSIONS: In our cases, the generators of myoclonus seemed to be most commonly located in the midthoracic lesion of the spinal cord with up and down propagation of slowly conducting pathways, such as propriospinal fibers. Cervical trauma can lead to the partial release of a spinal pattern generator, which is capable of recruiting muscles through long propriospinal pathways into complex rhythmic activity.