Mechanism of prolonged central motor conduction time in compressive cervical myelopathy

Objective: To investigate the mechanism of prolonged central motor conducti on time (CMCT) in compressive cervical myelopathy, we compared the calculat ed CMCT following transcranial magnetic stimulation (TCM) and evoked spinal cord potentials (ESCPs) following transcranial electric stimulation (TCE). Method: Motor evoked potentials following TCM were recorded from abductor d igiti minimi and abductor hallucis brevis muscles in 16 patients with compr essive cervical myelopathy. CMCT was calculated by subtracting peripheral c onduction time using peripheral nerve stimulation from MEP latency. ESCPs f ollowing TCE were recorded intraoperatively from posterior epidural space. Results: CMCT was prolonged and significant attenuation of the ESCP amplitu de following TCE was observed in all patients with cervical myelopathy. In 8 of 16 patients CMCT was significantly prolonged but ESCPs were recorded a t the C6-7 level with normal negative peak latency. Conclusions: Prolonged CMCT may occur with only a minor amount of conductio n slowing in the corticospinal tract in compressive cervical myelopathy. Im paired temporal summation of multiple descending potentials following TCM p roduced delays of motor neuron firing that contribute to the mechanism of p rolonged CMCT. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.