Somatosensory evoked potentials in cervical spondylosis. Correlation of median, ulnar and posterior tibial nerve responses with clinical and radiological findings.

Somatosensory evoked potentials (SEPs) following median, ulnar and tibial nerve stimulation were recorded from sites over the shoulders, neck and scalp in 34 patients with cervical spondylosis. Twenty control subjects were matched for sex and age. Detailed clinical and radiological data were assembled, with particular attention to the sensory modalities impaired and the locus and severity of cord compression. The patients were divided clinically into 4 groups: combined myelopathy and radiculopathy (6 cases), myelopathy alone (15), radiculopathy (6) and neck pain (7). Four cases are described in detail. SEP abnormalities were strongly correlated with clinical myelopathy, but not with radiculopathy. Median and ulnar nerve responses were less often affected than tibial, even with myelopathy above C6 level. Tibial nerve SEP abnormalities were strongly correlated with posterior column signs on the same side of the body, but not with anterolateral column sensory signs. In myelopathy cases, the SEP examination appeared to be more sensitive to sensory pathway involvement than clinical sensory testing. SEP abnormalities were infrequent in cases of radiculopathy and neck pain, bearing no relation to the clinical locus of root lesions. Abnormal SEPs consistent with subclinical posterior column involvement, however, were recorded in 1 patient with radiculopathy and 2 with neck pain. Follow-up recordings made postoperatively in 7 myelopathy cases reflected the clinical course (improvement, deterioration or no change) in 4, but failed to reflect improvement in 3. The correlation of SEP findings with radiological data was generally poor. SEP abnormalities were detected in 6 out of 8 patients with clinical myelopathy but no radiological evidence of posterior cord compression, suggesting that impairment of the blood supply may be an important factor contributing to cord damage. An application for SEPs in the clinical management of cervical spondylosis may lie in the detection of posterior column involvement and the differential diagnosis from disorders such as multiple sclerosis and amyotrophic lateral sclerosis.