Compound Muscle Action Potentials Under Dynamic Stress in Lumbar Spinal Canal Stenosis

Intermittent claudication is one of the characteristic symptoms in lumbar spinal canal stenosis. We recorded compound muscle action potentials (CMAPs) from the extensor digiti brevi (EDB) and the abductor hallucis (AH) before and after dynamic stress elicited by cauda equina electrical stimulation or transcranial magnetic stimulation. In 12 cases of 25 patients, the amplitudes of the CMAPs from the EDB or the AH elicited by cauda equina electrical stimulation decreased transiently, and recovered to the status of the control gradually within 5 min. In four cases of six patients, the amplitudes of the CMAPs elicited by transcranial magnetic stimulation decreased temporarily, and recovered to the status of the control within six minutes. It was suggested that a rapidly reversible physiological block by ischemia on the chronic injured cauda equina was the cause of the neurogenic intermittent claudication.