| BackgroundAbnormal muscle response(AMR)has been considered as a specific electrophysiological index for the diagnosis of hemifacial spasm(HFS).In microvascular decompression(MVD),surgeons usually evaluate the reliability and validity of the decompression by observing whether the AMR disappears or not.However,its predictive value has always been controversial when using the traditional qualitative method.ObjectiveThe objective of this work was to trace the changing AMR-elicited threshold value quantitatively and to analyse the possible reasons for the inconsistencies between the intraoperative observation and the postoperative results in traditional monitoring,so that a meliorated method of AMR monitoring could be given.MethodsSeventy two consecutive patients with primary HFS treated by MVD in department of neurosurgery,China-Japan friendship hospital between January 2014 and June 2014 were included in this study.A single square stimulus with intensities from 1mA to 100 mA was applied in AMR monitoring.The AMR-elicited threshold value and the amplitude of the main AMR waveform were traced throughout all surgical procedures.Those changes were divided into five patterns,including pattern A(stable disappearance),pattern B(major fluctuation),pattern C(minor fluctuation),pattern D(decreased amplitude only)and pattern E(stable persistence).As comparison,the traditional binary classification was also applied,dividing the changes into two patterns,including pattern disappearance and pattern persistence.According to the postoperative symptom,the clinical outcomes of the patients were classified into the following three groups:immediate cure,delayed cure,and no cure.Those two classifications were analysed and compared together with the postoperative clinical outcomes.Results(1)The mean follow-up duration was 27 months.Of the 72 patients,44 were immediately cured and 24 were delayed cured,the remaining 4 were proved to be not cured in their follow-up periods.(2)The numbers of patient in patterns A to E was presented below:pattern A(stable disappearance)26,pattern B(major fluctuation)12,pattern C(minor fluctuation)16,pattern D(decreased amplitude only)13 and pattern E(stable persistence)5.When traditional binary classification applied,the numbers of patient in pattern disappearance and persistence were 41 and 31,respectively.(3)The percentages of patterns A to E in group of immediate cure were 57%(25/44),16%(7/44),9%(4/44),16%(7/44),and 2%(1/44),respectively.The percentages of patterns A to E in group of delayed cure were 4%(1/24),21%(5/24),50%(12/24),25%(6124),and 0%(0/24),respectively.Those 4 cases in group of not cure(100%,4/4)were found all in pattern E.The difference in the constituent ratio was significantly different between any two groups.(4)When traditional binary classification applied,the percentages of patterns disappearance and persistence in group of immediate cure were 66%(29/44)and 34%(15/44),respectively.The percentages of patterns disappearance and persistence in group of delayed cure were 50%(12/24)and 50%(12/24),respectively.Those 4 cases in group of not cure(100%,4/4)were found all in pattern persistence.The difference in the constituent ratio was not significantly different between any two groups.Conclusions(1)A quantitative method by applying a wide range of stimulus intensities could discriminate more patterns of intraoperative AMR changes than traditional qualitative method.(2)The changes of the AMR-elicited threshold values might reflect the excitability of abnormal facial motor neurons but not the binary statuses of offending vessels(contact with the root exit zone of the facial nerve or not). |
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