Stimulus-sensitive spinal myoclonus.

Two cases of spinal myoclonus are described; in both patients myoclonus was responsive to stimuli and absent during sleep. The first patient was considered to have viral neuronitis and the condition resolved spontaneously. The second patient had spinal cord ischaemia; there was electro-physiological evidence of abnormal alpha motor neurone activity and histological study of the spinal cord revealed a severe reduction in small and intermediate neurones. This supports the theory that spinal myoclonus may result from abnormal activity of alpha motor neurones released from control by spinal internuncial neurones.