Mechanism of prolonged central motor conduction time in compressive cervical myelopathy.
OBJECTIVE
To investigate the mechanism of prolonged central motor conduction time (CMCT) in compressive cervical myelopathy, we compared the calculated CMCT following transcranial magnetic stimulation (TCM) and evoked spinal cord potentials (ESCPs) following transcranial electric stimulation (TCE).


METHODS
Motor evoked potentials following TCM were recorded from abductor digiti minimi and abductor hallucis brevis muscles in 16 patients with compressive cervical myelopathy. CMCT was calculated by subtracting peripheral conduction time using peripheral nerve stimulation from MEP latency. ESCPs following TCE were recorded intraoperatively from posterior epidural space.


RESULTS
CMCT was prolonged and significant attenuation of the ESCP amplitude following TCE was observed in all patients with cervical myelopathy. In 8 of 16 patients CMCT was significantly prolonged but ESCPs were recorded at the C6-7 level with normal negative peak latency.


CONCLUSIONS
Prolonged CMCT may occur with only a minor amount of conduction slowing in the corticospinal tract in compressive cervical myelopathy. Impaired temporal summation of multiple descending potentials following TCM produced delays of motor neuron firing that contribute to the mechanism of prolonged CMCT.
Kaneko
K
K
Department of Orthopedic Surgery, Yamaguchi University School of Medicine, 1-1-1 Minami-Kogushi, Ube, 755-8505, Yamaguchi, Japan.
Taguchi
T
T
Morita
H
H
Yonemura
H
H
Fujimoto
H
H
Kawai
S
S
D000368:Aged; D002574:Cervical Vertebrae; D004558:Electric Stimulation; D055590:Electromagnetic Phenomena; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013116:Spinal Cord / Q000502:physiology; D013117:Spinal Cord Compression / Q000503:physiopathology* / Q000601:surgery; D018709:Statistics, Nonparametric