Magnetic coil stimulation of the human lumbosacral vertebral column: site of stimulation and clinical application.

We describe the technique of magnetic coil (MC) stimulation of the lumbosacral roots and the possible site of stimulation in 22 control subjects, and the clinical usefulness of MC stimulation in 5 patients with low back pain. We observed 2 components in the compound muscle action potential of the soleus muscle following MC stimulation over the lumbosacral region. The second component had the physiological properties of the H reflex. The conduction time from the anterior horn cells of the lumbosacral spinal cord to the site of nerve root stimulation over the lumbosacral vertebral column was indirectly calculated as between 3.9 and 4.1 msec. Assuming a conduction velocity of 50 m/sec this would represent a distance of approximately 20 cm from the spinal motor neurons. Based on our control and patient data we conclude that the MC stimulation may be an useful technique for the diagnosis of lumbosacral radiculoplexopathy.