The contribution of magnetic stimulation of the motor cortex to the diagnosis of cervical spondylotic myelopathy. Correlation of central motor conduction to distal and proximal upper limb muscles with clinical and MRI findings.

Magnetic stimulation of the motor cortex and cervical spine was performed on 24 patients with cervical spondylotic myelopathy documented by MRI. Compound motor action potentials (CMAPs) were recorded from the biceps and thenar muscles to study the central motor pathways of two different myotomes, C5-C6 and C8-D1. Central motor conduction was abnormal in all 24 patients for thenar muscles and in 5 patients for biceps brachii. In patients with a single compression level, central motor conduction abnormalities were confined to the myotomes caudal to the site of compression documented by MRI, in both proximal and distal upper limb muscles in the patients with upper spondylotic compression, and in distal muscles only in the patients with lower compression. In the patients with multilevel compression, central motor conduction time was abnormal for thenar muscles and always normal for the biceps muscle, but its mean value was significantly greater than in the control subjects, suggesting a slight involvement of central motor pathways for proximal upper limb muscles and major damage of the lower cervical segments. Owing to their high degree of sensitivity, central motor conduction studies may be of considerable value in the functional assessment of central motor pathways in cervical spondylotic myelopathy.