Motor-evoked potentials in diabetes mellitus

By using magnetic stimulation of the motor cortex and in the cervical region, conduction time in the central motor pathway was measured in 35 patients with diabetes mellitus (DM) and in 41 control subjects. Motor-evoked potentials (MEPs) were recorded from the contralateral thenar muscles. Central conduction time (CCT) was obtained by subtracting the latency of the spinal MEP from that of the scalp MEP. To compare central and peripheral nerve functions, the motor nerve conduction velocity (MCV) of the median nerve was also tested in patients with DM. In the 35 cases of DM, the mean latency of the cortical MEPs showed a significant increase, compared with normal controls; the mean CCT was also significantly prolonged in the patient group. There was a good correlation between central motor abnormalities and the duration of DM, as well as with impairment of the peripheral nervous system. Latencies of greater than two standard deviations were defined as abnormal. The abnormal rate in patients with DM was 29% for latency of the cortical MEP, 20% for latency of the cervical MEP and 37% for the CCT. In addition, there was a 35% abnormal rate for distal latency of the median MCV and a 40% abnormal rate for the median MCV. These findings support the theory that the metabolic disturbance in DM affects both the central and peripheral nervous systems in man. MEP studies provide objective measurements of central motor pathways.