title: Monitoring of abnormal muscle response and facial motor evoked potential during microvascular decompression for hemifacial spasm.
abstract: BACKGROUND
  To determine whether the monitoring of abnormal muscle response (AMR) and facial motor evoked potential (FMEP) during microvascular decompression (MVD) for hemifacial spasm (HFS) might be useful for predicting the postoperative clinical course and final outcomes.
  
  
  METHODS
  We analyzed 45 HFS patients who underwent both AMR and FMEP monitoring during MVD. Patients were divided into two groups on the basis of post-MVD disappearance (group AMR-A) or persistence (group AMR-B) of AMR. With regard to FMEPs, patients were classified into one of the two groups according to the ratio of the final to baseline FMEP amplitudes recorded for the orbicularis oculi muscle: one group with a ratio of <50% (group FMEP-A), and the other with a ratio of ≥50% (group FMEP-B).
  
  
  RESULTS
  Twenty-one of the 26 (81%) patients in group AMR-A were assigned to group FMEP-A, whereas 9 of the 17 (53%) patients in group AMR-B were assigned to FMEP-B (P < 0.05). In 38 of the 40 (95%) patients in whom the AMRs disappeared or persisted at amplitudes <50% that at the baseline, HFS had subsided at the final follow-up. Forty of the 42 (95%) patients whose FMEP amplitude ratios indicated reduction in the amplitudes from the baseline, had complete relief of the symptoms. Nineteen of the 20 (95%) patients whose AMRs disappeared after MVD experienced immediate relief of their symptoms after the operation. With regard to 14 of the 20 (70%) patients whose AMRs persisted at the final recordings, the symptoms of HFS improved over time and eventually subsided (P < 0.001).
  
  
  CONCLUSIONS
  Intraoperative monitoring of both AMR and FMEP during MVD may be useful in predicting the postoperative outcomes in HFS patients. The AMR-related findings may help to predict whether HFS disappears immediately after surgery or some time later.
authors.affiliation: Department of Neurosurgery, Brain Research Institute, University of Niigata, Asahimachi-dori, Chuo-ku, Niigata-City, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Fukuda
authors.forename: Makoto
authors.initials: M
authors.lastname: Oishi
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Takao
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hiraishi
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Sato
authors.forename: Yukihiko
authors.initials: Y
authors.lastname: Fujii