Short-latency somatosensory evoked potentials in patients with cervical compressive lesions: morphological versus functional examination.

We studied short-latency somatosensory evoked potentials (SSEPs) elicited by upper limb stimulation in 40 patients with cervical compressive lesions. Of these, 17 underwent MRI examination and the remaining 23 had myelography for the assessment of structural changes. The latencies of N11 and N13 recorded from the neck and P14 derived from the scalp were used to calculate the interpeak latencies from the Erb's point potential. Abnormalities of N11 implied a nerve root lesion whereas those of N13 with normal N11 indicated cervical cord involvement. In patients with normal N11 and N13, prolongation of P14, originating from the medial lemniscus, indicated a compressive lesion located above the level of entry to the spinal cord of the nerve stimulated. When MRI showed abnormal signals in the spinal cord, N11 or N13 or both were generally affected. SSEPs also detected functional abnormalities in the absence of morphologic changes on MRI. These findings suggest that SSEP is a sensitive technique to use as a test of functional integrity of the spinal cord.