A noninvasive technique to assess completeness of spinal cord lesions in humans.

The effect of scalp stimulation delivered through electrodes overlying the motor cortex was evaluated in five healthy subjects and six patients with traumatic spinal cord injury. The latency to the onset of the electromyographic response was measured in the biceps brachii and abductor pollicis brevis muscles. In all the patients, latencies to the muscle (biceps brachii) whose innervation originated above the lesion were in the normal range; whereas, latencies to the muscle (abductor pollicis brevis) whose innervation originated below the lesion were prolonged. Electromyographic signals were recorded in muscles which showed no voluntary motor activity. No lateral differences in latencies were found in healthy subjects; however, in the patients, significant differences were obtained between the right and left abductor pollicis brevis muscles. The results of this study demonstrate that the spinal cord of patients with a lesion deemed to be clinically complete, contains nerve fibers which descend through the lesion and are capable of conveying impulses leading to muscle contraction.