Cortical somatosensory potentials evoked by magnetic stimulation of thoracic and lumbar roots.

We applied twin coil magnetic stimulation to thoracic and lumbar roots to evaluate the posterior column function in 50 normal subjects and 34 patients with neurologic disorders. In all nine patients with cervical myelopathy, there were abnormal somatosensory evoked potentials (SEPs) with stimulation of upper thoracic levels. In 14 patients with thoracic or lumbar myelopathy, there were normal SEPs with stimulation of spinal roots above the lesions and abnormal SEPs with stimulation below the lesions. In a patient with girdle sensation between T-3 and T-6, the peak latencies of P2 were significantly delayed with stimulation of T-2 and T-4, but peak latencies were normal with T-6, T-10, and L-3 stimulation. Ten patients with polyneuropathy had normal SEPs recorded with thoracic and lumbar root stimulation. SEPs by twin coil stimulation at thoracic and lumbar root levels are useful in detecting lesions of spinal cord or roots and for following their clinical course noninvasively.