Assessment of Cervical Myelopathy Using Transcranial Magnetic Stimulation and Prediction of Prognosis After Laminoplasty

Abstract

This study investigated the clinical usefulness of motor-evoked potentials (MEPs) produced by transcranial magnetic stimulation of the brain for cervical myelopathy patients. The purpose of this study was to determine the usefulness of MEPs for the assessment of the severity of myelopathy and prediction of the outcome of laminoplasty. Magnetic stimulation has been widely used for examination of the descending excitatory motor pathways in the central nervous system, but little attention has been paid to cervical myelopathy. We measured the MEPs of 56 patients who underwent surgery for cervical myelopathy. The MEPs from the abductor pollicis brevis, abductor digiti minimi, tibialis anterior, and abductor hallucis muscle were evoked by transcranial magnetic brain stimulation. The latency from the anterior horn cell of the spinal cord to the hand or foot muscles was also measured, with the F-value [(F + M - 1)/2] calculated. This was followed by estimation of the central motor conduction time (CMCT). Severity of clinical disability was scored on the basis of symptoms according to a modified ADL scale for cervical myelopathy of the Japanese Orthopedic Association (JOA) score. The average CMCT of the symptomatic side significantly correlated with the preoperative JOA score. The average CMCT of the symptomatic side significantly correlated with the 1-year postoperative JOA score. The average CMCT for patients with poor outcome was significantly longer than that for patients with good outcome. CMCT of 15 milliseconds or more in the upper extremities or that of 22 milliseconds or more in the lower extremities indicated poor prognosis. In patients with cervical myelopathy, the CMCT significantly correlated with the results of clinical assessment. These findings regarding the duration of CMCT may be useful parameters in spinal pathology for prediction of the outcome of surgical treatment.