Intraoperative evoked electromyography in Bell's palsy.

The technique of intraoperative evoked electromyography is described in detail. Direct intraoperative stimulation of the exposed facial nerve identified the sites of nerve impulse conduction blocks in 16 of 18 patients who needed decompression for Bell' s palsy. In order to determine the site of impulse conduction block the test must be performed before 100 per cent nerve degeneration occurs. The lesions extended only a few millimeters and were found to be proximal to the geniculate ganglion in 15 (94 per cent) of these patients. Schirmer's test correctly identified the sites of the lesions in only 61 per cent of the patients. To locate the precise site of the lesion inducing a conduction block in Bell's palsy, intraoperative evoked electromyography must be used. The limited extent of the blocked motor fibers indicates that segmental rather than total intratemporal decompression is needed in Bell's palsy.