[Short latency somatosensory evoked potentials in patients with syringomyelia]

Short latency somatosensory evoked potentials (SSEPs) following median nerve and posterior tibial nerve stimulation were studied in six patients with syringomyelia. Three patients had Chiari malformations, two patients experienced fracture of the spine and one patient had a cauda equina ependymoma. SSEPs following median nerve stimulation were abnormal in all patients, of which five patients showed abnormal SSEPs only in the unilateral stimulation on the side of sensory deficits. SSEPs obtained from three out of eight upper extremities which showed no disturbance of deep sensation, were abnormal, so SSEPs were able to detect subclinical abnormality indicating dorsal column dysfunction. Abnormal patterns of SSEPs were classified in three types as follows; Type 1: disappearance of P13, N16 and N18 (3 cases), Type 2: the prolonged interpeak latency P11-P13 (2 cases), and Type 3: abnormal N16 and N18 with preserving P13 (1 case with Chiari malformation). P9 and P11 were present without prolonged latencies in all cases. SSEPs following posterior tibial nerve stimulation were abnormal in two of the three tested patients. Those two patients had disturbance of deep sensations in the lower extremities. All patients underwent surgical treatment, syringo-peritoneal shunt in four patients, foramen magnum decompression with syringo-subarachnoid shunt in one patient, and total removal of an ependymoma of the cauda equina with syringotomy in one patient. Postoperative neurological improvement were found in three patients, of which two cases also showed improvement in SSEPs. On the contrary SSEPs were unchanged in two patients with posttraumatic syringomyelia, whose postoperative neurological condition was also unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)