Clinical correlates of abnormal P14 in median SEPs

Recording median somatosensory evoked potentials (SEPs) from scalp and neck in separate channels with the use of an ear reference, 52 patients had abnormal scalp-recorded P14 associated with normal cervical-recorded N13. The patients had multiple sclerosis or other brainstem or high cervical cord lesions. Evidence of brainstem lesions was found in 35 patients on clinical examination or by brainstem auditory evoked potentials or blink reflex. Abnormalities of P14 were correlated highly with brainstem dysfunction, but high cervical cord lesions could not be excluded by this finding. The localizing value of SEP is improved by measuring the N13 and P14 peaks separately and assessing the cervical cord-brainstem conduction time.