Tibial Nerve Somatosensory Evoked Potentials in Spinal Cord Hemisection

Somatosensory evoked potentials (SEPs) have been studied in many disease states since they were first described by Dawson in 1947. However, there have been very few reports of SEP findings in patients with spinal cord hemisection. On the basis of clinical correlation, Giblin first postulated that the activity giving rise to the initial cortical components of the SEP travels through the dorsal column-lemniscal system. However, the pathway through which these evoked potentials are transmitted has recently been questioned. This paper examines the results of tibial nerve SEPS performed on four patients with spinal cord hemisection (Brown-Séquard syndrome). In all four cases presented, the impairment of cortical SEP components was consistently associated with stimulation of the leg ipsilateral to the side of cord injury. We conclude that the most likely mechanism of transmission is through the ipsilateral dorsal columnlemniscal system.