Cutaneous silent periods in intramedullary spinal cord lesions.

OBJECTIVE: The neurophysiological assessment of intramedullary spinal cord lesions has been unsatisfactory. Previous studies in patients with syringomyelia suggest that testing of cutaneous silent periods (CSPs) may be useful to assess centromedullary lesions.

METHODS: The authors studied nine patients with intramedullary spinal cord lesions of different etiologies. Eight patients with cervical lesions presented with hypalgesia, hypothermesthesia, or pain in at least one upper extremity; five of them had also upper limb weakness or sensory impairment. One patient with a thoracic lesion had normal upper limb function. The authors recorded CSPs in abductor pollicis brevis muscle following digit II and digit V stimulation. Somatosensory evoked potentials (SEPs) were obtained following median and tibial nerve stimulation. Motor evoked potentials (MEPs) were obtained in biceps brachii, abductor digiti minimi and tibialis anterior muscles following transcranial magnetic or electrical stimulation.

RESULTS: CSP abnormalities were found in all patients with cervical lesions, but not in the patient with a thoracic lesion. Cortical median nerve SEPs had normal latencies in all patients, while tibial nerve SEPs, upper limb MEPs, and lower limb MEPs were delayed in five patients each. In one patient, abnormal CSP were the only neurophysiological finding. CSP abnormalities were associated with hypalgesia and hypothermesthesia in 95% of the studies.

CONCLUSION: Upper extremity CSP testing is a sensitive neurophysiological technique for the assessment of cervical intramedullary lesions. In particular, abnormal CSPs are highly associated with spinothalamic dysfunction.