MAGNETIC STIMULATION IN HEMIFACIAL SPASM AND POST FACIAL PALSY SYNKINESIS

The facial nerve was stimulated trascranially with a magnetic stimulat or in 14 normal controls, 14 hemifacial spasm patients, and 16 post-fa cial-palsy synkinesis patients. Magnetic stimulation in normal control s revealed muscle responses which had latencies with a mean value of 4 .99 +/- 0.49 ms and amplitudes of 2.41 +/- 1.08 mV. In the same group, transosseal conduction time was calculated to be 1.20 +/- 0.13 ms. In the hemifacial spasm group, the amplitudes of the responses on the af fected sides were lower as compared to the unaffected sides (mean valu es 1.78 vs. 2.41 mV, P = 0.01). Also, the threshold to magnetic stimul ation was elevated on the affected sides. These findings are suggestiv e of the presence of a hypoexcitability to magnetic stimulation in the root entry zone. In the post-facial-palsy synkinesis patients, magnet ic stimulation of the affected sides resulted in responses with long l atencies and low amplitudes (mean latency 6.34 ms, mean amplitude 0.90 mV). In the recordings made with magnetic stimulation, the difference of the latencies between the two sides was larger as compared to thos e obtained by electrical stimulation. The transosseal conduction time was also remarkably prolonged on the affected side. These findings may suggest that magnetic stimulation can be an effective method of showi ng intracranially located lesions of the facial nerve. (C) 1993 John W iley & Sons, Inc.