The value of magnetic stimulation in the diagnosis of radiculopathies.

We studied 42 patients with cervical and lumbar radiculopathies using magnetic stimulation. Prolonged latencies following magnetic stimulation of the brain, the paravertebral spinal nerve, or both, showed a highly significant correlation with muscle weakness in clinical testing (24 of 26 patients with weakness had pathological motor evoked potentials) as well as with spontaneous activity of the target muscles in needle electromyography (24 of 25 subjects). The determination of both the central and the peripheral motor conduction time was found to be essential in patients with radiculopathies, because different patterns of latency changes correlated with different morphological results in computed tomography: in patients diagnosed as having a lateral compression of the nerve root the peripheral nerve latency was delayed; whereas, in patients with more medially localized herniations, a prolonged central motor latency was the most frequent finding. This study posits that combined magnetic stimulation of the brain and nerve root is an effective and painless technique for the noninvasive evaluation of nerve root function.