[A case of stimulus-sensitive spinal myoclonus].

A 64-year-old man was admitted to our hospital because of a 2-year progression of muscular jerks on the bilateral thoracic and abdominal walls. Neurological examination was normal except for myoclonus localized in the bilateral Th5 to L1 segments. Myoclonus in this case was symmetrical and synchronous, and had a tendency to continue rhythmically. It was also segmental and considered to be spinal in origin. The interval between two adjacent myoclonic jerks was short when the amplitude and duration of the first myoclonus were high and long, respectively. We postulated that the activity of anterior horn cells at an impaired segment might be a factor that influences the resting time between jerks. A myoclonic jerk could be induced by a tendon tap given anywhere on this patient's body, with a latency ranging from 40 to 220 msec, irrespective of the sites of tapping. A long latency and polysynaptic reflex may participate in such stimulus sensitivity. The site of the reflex was probably above the motor nucleus of the trigeminal nerve, because jerks could be induced by jaw taps. Our observations support the theory that a spino-bulbo-spinal reflex is manifested at the impaired segment.