Magnetic stimulation in hemifacial spasm and post-facial palsy synkinesis

The facial nerve was stimulated trascranially with a magnetic stimulator in 14 normal controls, 14 hemifacial spasm patients, and 16 post-facial-palsy synkinesis patients. Magnetic stimulation in normal controls 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 affected sides were lower as compared to the unaffected sides (mean values 1.78 vs. 2.41 mV, P = 0.01). Also, the threshold to magnetic stimulation was elevated on the affected sides. These findings are suggestive of the presence of a hypoexcitability to magnetic stimulation in the root entry zone. In the post-facial-palsy synkinesis patients, magnetic stimulation of the affected sides resulted in responses with long latencies 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 those 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 showing intracranially located lesions of the facial nerve.