Somatosensory potentials evoked by magnetic stimulation of lumbar roots, cauda equina, and leg nerves.

Cortical somatosensory evoked potentials (SEPs) were studied by noninvasive magnetic stimulation at T-10, T-12, and L-5 vertebral levels and in mid-gluteus muscle and ankle in 27 normal subjects and 7 patients with neurological diseases. Cortical components P2 and N2 were recorded in all normal subjects. The mean peak latencies of P2 were 20.3 +/- 0.9 (standard deviation), 21.1 +/- 1.2, 23.5 +/- 1.4, 27.9 +/- 2.0, and 38.1 +/- 1.8 msec at the T-10, T-12, L-5, midgluteal and ankle sites of stimulation, respectively. No substantial difference in morphology of P2 and N2 was seen between magnetic and electrical stimulation at T-12. Amplitudes of P2 and N2 were maximal after magnetic stimulation at motor threshold. P2 and N2 may originate from the sensory cortex. P2 and N2 evoked by T-10 and T-12 stimulation were normal in peak latency and morphology in patients with polyneuropathy or polyradiculoneuropathy. Peak latencies of P2 and N2 evoked by T-10 and T-12 stimulation were significantly delayed in patients with myelopathy. The patients with radiculopathy showed a delayed peak latency and conduction time of P2 evoked by L-5 stimulation. Magnetic stimulation of spinal root is able to detect lesions of spinal cord noninvasively.