Evaluation of corticospinal excitability in cervical myelopathy, before and after surgery, with transcranial magnetic stimulation: a pilot study

Abstract

Purpose: A pilot study to examine the impact of cervical myelopathy on corticospinal excitability, using transcranial magnetic stimulation, and to investigate whether motor evoked potential (MEP) and silent period (SP) recruitment curve (RC) parameters can detect changes in corticospinal function pre- and post-surgery.

Methods: We studied six cervical myelopathy patients undergoing surgery and six healthy controls. Clinical and functional scores and neurophysiological parameters were examined prior to and 3 months following the surgery.

Results: MEP latencies for abductor pollicis brevis (APB) and tibialis anterior (TA) muscles and central motor conduction time were prolonged pre- and post-surgery; SP durations were differentially altered. There were significant differences in parameters of RCs for (1) MEP area in APB (max values, S50) and TA (slope) between controls and patients pre- and post-surgery and (2) SP duration in APB (max values) between patients pre-surgery and controls.

Conclusions: The findings of this pilot study suggest an uncoupling of excitatory and inhibitory pathways, which persists at 3 months following cord decompression. RCs for MEP and SP at 3 months provide more information on the functional status of the cord and prompts for a longer term follow-up.

Fig. 1

Mean (±SEM) ASIA motor (upper left panel) and sensory (upper right panel) scores and Pegboard test time (lower left panel) and shuttle walking distance (lower right panel) in the patients prior to and following surgery

Fig. 2

Mean (±SEM) MEP latency of responses recorded from APB (left panel) and TA (right panel) following TMS to the motor cortex at the maximum stimulus intensity used (100 % MSO for APB and 70 %MSO for TA)

Fig. 3

Mean (±SEM) CMCT calculated from responses recorded from APB (left panel) and TA (right panel) following TMS to the motor cortex at the maximum stimulus intensity used (100 % MSO for APB and 70 %MSO for TA)

Fig. 4

Stimulus response curves showing mean (±SEM) MEP area recorded from APB (left panel) and TA (right panel) following TMS to the motor cortex at differing stimulus intensities. The lines are applied to the mean data for each group using the Boltzmann function (see text for details)

Fig. 5

Stimulus response curves showing mean (±SEM) silent period duration in the electromyogram recorded from APB (left panel) and TA (right panel) following TMS to the motor cortex at differing stimulus intensities. The lines are applied to the mean data for each group using the Boltzmann function (see text for details)