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. 1998 Jul;65(1):80-7.
doi: 10.1136/jnnp.65.1.80.

Responses of thenar muscles to transcranial magnetic stimulation of the motor cortex in patients with incomplete spinal cord injury

N J Davey  1 , H C Smith, E Wells, D W Maskill, G Savic, P H Ellaway, H L Frankel
Affiliations

Responses of thenar muscles to transcranial magnetic stimulation of the motor cortex in patients with incomplete spinal cord injury

N J Davey et al. J Neurol Neurosurg Psychiatry. 1998 Jul.

Abstract

Objective: To investigate changes in electromyographic (EMG) responses to transcranial magnetic stimulation (TMS) of the motor cortex after incomplete spinal cord injury in humans.

Methods: A group of 10 patients with incomplete spinal cord injury (motor level C3-C8) was compared with a group of 10 healthy control subjects. Surface EMG recordings were made from the thenar muscles. TMS was applied with a 9 cm circular stimulating coil centred over the vertex. The EMG responses to up to 50 magnetic stimuli were rectified and averaged.

Results: Thresholds for compound motor evoked potentials (cMEPs) and suppression of voluntary contraction (SVC) elicited by TMS were higher (p < 0.05) in the patient group. Latency of cMEPs was longer (p < 0.05) in the patient group in both relaxed (controls 21.3 (SEM 0.5) ms; patients 27.7 (SEM 1.3) ms) and voluntarily contracted (controls 19.8 (SEM 0.5) ms; patients 27.6 (SEM 1.3) ms) muscles. The latency of SVC was longer (p < 0.05) in the patients (51.8 (SEM 1.8) ms) than in the controls (33.4 (SEM 1.9) ms). The latency difference (SVC-cMEP) was longer in the patients (25.3 (SEM 2.4) ms) than in the controls (13.4 (SEM 1.6) ms).

Conclusion: The longer latency difference between cMEPs and SVC in the patients may reflect a weak or absent early component of cortical inhibition. Such a change may contribute to the restoration of useful motor function after incomplete spinal cord injury.

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