[Motor evoked potentials in patients with cervical spondylotic myelopathy]

We applied somatosensory and motor evoked potential studies to investigate patients with cervical spondylotic myelopathy (CSM) diagnosed clinically and roentgenographically. There were 32 consecutive cases collected, including 25 males and 7 females, at an average age of 62 +/- 8.2 (49-75) years. A control group consisted of 30 healthy subjects matched in body height and age with patients. The normal values of head-to-neck and head-to-lumbar region central motor conduction times (CMCTs) were 7.04 +/- 0.60 (6.1-8.2) and 15.94 +/- 1.23 (14.0-18.7) ms, which were not affected by body height. The somatosensory evoked potential (SEP) findings were related to clinical posterior column signs, levels of cord lesion, and nerves tested. The abnormality rate of median nerve SEP was relatively low, 53% (17/32), particularly for the lesion below C5-6 level in which median nerve SEP was usually normal. The abnormality rates of ulnar and tibial nerve SEPs were up to 84.5% (27/32) and 90.6% (29/32) respectively. However, median, ulnar and tibial nerve SEPs were normal in 3 (9.4%) patients showing normal posterior column function clinically. Only 18 (56.3%) patients had recordable motor evoked potential (MEP) from abductor digiti minimi (ADM) to head stimulation. The head-to-neck CMCT, 9.12 +/- 1.53 (6.3-12.7) ms, was significantly prolonged. Of these 18 cases there were 9 cases of delayed CMCT with reduced MEP amplitude, 4 of delayed CMCT, 3 of reduced MEP amplitude, and 2 of normal CMCT and MEP amplitude. The remaining 14 cases (43.7%) showed absent MEP from ADM to head stimulation. The overall abnormal rate of MEP from ADM was 93.8% (30/32). MEP from tibialis anterior (TA) to head stimulation was recorded only in 6 patients in whom the responses were all abnormal. There was no response recorded from TA in the remaining 26 CSM patients.(ABSTRACT TRUNCATED AT 250 WORDS)