Early permanent disappearance of abnormal muscle response during microvascular decompression for hemifacial spasm: a retrospective clinical study

The objective of this study is to explore the cause of early abnormal muscle response (AMR) disappearance during microvascular decompression for hemifacial spasm and the clinical outcomes of these patients. Three hundred seventy-two patients received microvascular decompression (MVD) under intraoperative electrophysiological monitoring in Nanjing Drum Tower Hospital in 2014; the characteristic AMR of HFS was observed in 359 patients during the operation. And the 359 patients were divided into two groups based on whether AMR had remained before the beginning of the decompression procedure for offending vessels. Thirty-three patients who showed a permanent disappearance of AMR before the beginning of decompression were regarded as group I. Dural opening and the succeeding CSF drainage produced a permanent disappearance of AMR in 13. During the dissection of lateral cerebellomedullary cistern, a permanent disappearance of AMR was found in 20 patients. Thirty-two patients were cured immediately; delayed resolution (7 days after surgery) was found in one patient. No complications were observed and no recurrence was found during the follow-up period in the 33 patients. In the other 326 patients (group II), AMR disappeared temporarily before the beginning of the decompression procedure for offending vessels in 42 patients. After decompression, AMR disappeared completely in 305 patients. Two hundred sixty-seven patients were cured immediately and 57 patients got a delayed resolution (2 days to 45 weeks after surgery). The two left did not get a complete abolition of spasm. Three cases of hearing loss, one hoarseness, and nine delayed facial paralysis were observed. The reason of early abnormal muscle response disappearance may be that the degree of neurovascular compression was not serious; these patients were more likely to get an immediate cure. Continuous intraoperative electrophysiological monitoring of AMR is necessary.