Measurement of motor conduction in the thoracolumbar cord. A possible predictor of surgical outcome in cervical spondylotic myelopathy.

Abstract

A prospective motor-evoked potential study with measurement of spinal cord motor conduction velocity in the thoracolumbar cord was performed before and after decompression surgery in 30 patients with cervical spondylotic myelopathy. To evaluate the neurofunctional integrity of the spinal motor pathways in cervical spondylotic myelopathy in patients compared with age-matched control subjects; to assess any changes after posterior surgical decompression; and to correlate such changes with functional outcomes so that the predictability of preoperative motor-evoked potentials could be determined. Previous studies evaluating neurologic function and predictability of surgical results in cervical spondylotic myelopathy patients always depended on the morphologic changes of the cord and spinal structures. The recently developed motor-evoked potential study and noninvasive measurement of spinal cord motor conduction velocity may provided an objective method to evaluate physiologic motor function in cervical spondylotic myelopathy patients. Spinal cord motor conduction velocity in the thoracolumbar cord was measured using percutaneous magnetic stimulation over the motor cortices and F-wave studies in median and peroneal nerves. Motor function of cervical spondylotic myelopathy patients was graded according to evaluation of signs of cord involvement, ambulation, and degree of dependence in activities of daily living. Evaluation was performed at 6 months, 1 year, and 2 years after decompression surgery. Motor functional improvement accompanied by increased spinal cord motor conduction velocity occurred in Grade I patients with a mild neurologic dysfunction but not in Grade II or III patients with a moderate-to serve neurologic deficit. Neurologic improvement does not appear to occur until 6 months after surgery. Measurement of spinal cord motor conduction velocity may provide an objective and quantitative approach to assessing the motor functional integrity of the spinal cord and serving as a predictor in evaluating surgical outcome in patients with cervical spondylotic myelopathy.