MOTOR-EVOKED POTENTIALS FROM MULTIPLE-TARGET MUSCLES IN MULTIPLE-SCLEROSIS AND CERVICAL MYELOPATHY

Motor-evoked potentials (MEP) from abductor digiti minimi (ADM), bicep s brachii (BE) and tibialis anterior (TA) muscle were analysed in 101 patients with multiple sclerosis (MS) and in 72 patients with compress ive cervical myelopathy (CM). In definite MS the results were abnormal in 82% and in probable or possible MS in 64% of patients. In CM resul ts were abnormal in 56% when the compression site was at the C4/C5 int erspace or higher (CM(C1-C4-)), and in 100% when the compression fell between the C5 and C7 level (CM(C5-C7)). The pattern of normal respons es from BE with abnormal responses from ADM was found in 37% of patien ts with CM(C5-C7), in 10% of patients with MS (p = 0.01) and in 19% of patients with CM(C1-C4+). Abnormal MEP from both ADM and BE were sign ificantly more frequent in MS than in CM (p = 0.002). Although ''speci fic patterns'' of MEP abnormality could be significantly correlated wi th patient groups and anatomical compression sites, they cannot be tak en as a reliable diagnostic clue in the individual case. In particular , abnormal responses from BE were frequently also found in CM(C5-C7). These discrepancies cannot be explained on the basis of a localized me chanical mechanism and raise the question of the pathogenesis in CM.