Clinical Application of Motor Evoked Potentials in Disorders of the Spine

Summary

Transcranial and spinal magnetic stimulation was performed on 62 healthy adults to obtain normal values of central motor conduction times to cervical and lumbar segments innervating limb muscles. The mean central motor latency (CML) was 5.1 ms when recording from the biceps brachii and 5.2 ms when recording from the abductor pollicis brevis or abductor digiti minimi muscles. The mean CML to lower limb muscles were 13.0 ms to the quadriceps femoris, 13.3 ms to the anterior tibial, and 13.4 ms to the extensor digitorum brevis muscles. Conduction times higher than “mean latency + 2 × standard deviation” may indicate a pathological conduction slowing.

Some 136 patients with cervical spine disorders were examined. Of all patients 76% showed a pathological delay of their motor evoked potentials (MEP) to upper limb muscles. Of 52 patients with lumbar spine disorders 63% showed pathologically delayed MEP to lower limb muscles.

Magnetic stimulation of the motor system is a painless neurophysiological technique which enables us to examine the central motor pathways in awake subjects with respect to disorders of the spine. This method offers important additional information in conditions such as compression of the spinal cord or of the motor roots.