Transcranial magnetic stimulation for detection of preclinical cervical spondylotic myelopathy.

Twenty-three patients, mean age 50.4 years, with cervical radiculopathy at C7 or more rostrally, were studied with electromyography, CT scans (in 16 cases) and transcranial magnetic stimulation. None had overt evidence of myelopathy. Motor evoked potentials (MEPs) were recorded from the hand muscles (C8/T1), and latency, amplitude, and the MEP/CMAP ratio and central motor delay between the hand motor cortex and the lower cervical spine were measured. One or more of these were abnormal in 15 of 23 cases (65%). The most common abnormality was a reduced MEP/CMAP ratio. The findings indicate that physiologic dysfunction of the spinal cord, caudal to a radiculopathy, frequently accompanies a radiculopathy and may antedate overt cervical spondylotic myelopathy. This may be valuable in directing more timely surgical intervention.