Somatosensory evoked potentials and motor cortex stimulation in myelopathies.

Short latency somatosensory evoked potentials (SSEPs) to stimulation of the tibial nerve at the ankle and at the knee and motor action potentials (MAPs) recorded from the tibial muscle during transcranial stimulation of the motor cortex were recorded in 21 patients with myelopathy. The electrophysiological results were compared with the clinical evolution over 12 months. Both scalp SSEPs and MAPs were absent in 10 patients with clinically 'complete cord transection.' The clinical and electrophysiological data remained unchanged in these patients. Scalp SSEPs were present at the first examination in all 11 patients with clinically 'incomplete cord lesion.' All these patients improved in the following year. The clinical recovery was almost complete in 3 patients who had normal scalp SSEPs but varied markedly in 8 patients with abnormal SSEPs. Normal MAPs were obtained in 1 of the 3 patients who showed the best clinical recovery. In the other subjects, MAP findings did not show a clear correlation with either the clinical signs or the course.