LONG-LATENCY RESPONSE TO TRANSCRANIAL MAGNETIC STIMULATION IN PATIENTS WITH HEMIFACIAL SPASM

Objective: We studied the long-latency response of the orbicularis ori s muscle elicited with transcranial magnetic stimulation in patients w ith hemifacial spasm (HFS) and evaluated the excitability of the facia l nucleus. Methods: We compared the thresholds on both sides in 8 norm al volunteers and 7 patients with hemifacial spasm. The thresholds wer e determined as the lowest intensity required to produce motor evoked potentials with an amplitude of at least 50 mu V in the orbicularis or is muscle. Average values were given as means +/- standard deviation. Wilcoxon's rank sum test was used for comparisons between the sides of normal subjects and of patients with HFS with respect to the threshol d stimulus. Results: There was no significant difference between the t hresholds on the two sides of the normal subjects (mean 1.88 +/- 5.30% , P > 0.05). In patients with HFS, there was a significant difference between the thresholds on the spasm side and the normal side (mean 20. 7 +/- 13.0%, P < 0 05) In one patient studied after MVD, the differenc e between both sides disappeared. Conclusion: The difference between t he thresholds in patients with HFS and the normalization in threshold after MVD suggested that the mechanism of HFS was hyperexcitability of the facial nucleus. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.