Monitoring of Facial Evoked EMG for Hemifacial Spasm: a Critical Analysis of its Prognostic Value

Abstract

Microvascular decompression (MVD) has come to stay as an effective way of treating hemifacial spasm. But it remains to be seen how much each of the electrophysiological monitoring techniques (intra-operative) are contributing to its increased efficacy. Their role as indicators for re-exploration or recurrence is to be evaluated with more studies. We have used the lateral spread response in those patients who had distinctly abnormal recording on the ipsilateral side, studied the intra-operative changes during MVD and correlated with the outcome of surgery. 38 patients operated for HFS, were selected for intra-operative monitoring of abnormal muscle responses. In 17 patients, there was persistence of abnormal muscle responses in the immediate postoperative period and only 6 of them had mild HFS. Two of 21 patients who had disappearance of abnormal responses had persistent mild HFS; but in all cases, the HFS disappeared within 3 months. So we found that the intra-operative recording was really not reliable in predicting the immediate postoperative outcome. However the outcome at 3 months suggested that waiting for some time before re-exploration is a better option, especially if the HFS had become mild.

Utility of intraoperative electromyography in microvascular decompression for hemifacial spasm: a meta-analysis

“…All studies in the English-language literature (searched with Ovid Medline) with > 30 patients, containing data on the presence or absence of the AMR at the conclusion of MVD and presence or absence of spasms at followup were included. 3,6,7,9,11,12,21,27,31 In these series, patients in whom the AMR disappeared during dural opening or manipulation of the cerebellum were discarded from analysis. Mooij et al 24 presented their data in an intuitive fashion.…”

“…12,[17][18][19]31 Since HFS disappears or gradually resolves over time in many patients in whom the AMR persists intraoperatively, however, many authors have questioned the usefulness of intraoperative EMG. 3,9,11,28 In a large study evaluating 300 patients, Kong et al 12 found a sta- tistical difference at the 1-year follow-up in the outcomes between 2 groups based on whether the AMR resolved or persisted. Their report is the only one that shows a statistically different outcome in cases in which the AMR did not resolve.…”

“…1,3,9,11,28 To date, there are no reported randomized controlled trials of intraoperative EMG that were designed or powered to study cure of HFS as the primary end point. Because the majority of surgeons performing MVD for HFS believe strongly about the use of intraoperative EMG, it is unlikely that a large prospective, randomized multicenter trial will be undertaken.…”

“…17 While several retrospective and prospective studies have strongly supported its use, 6,21,27,31 several other studies have failed to show that intraoperative EMG improves outcome (that is, a cure of HFS). 1,3,9,11,28 To date, there are no reported randomized controlled trials of intraoperative EMG that were designed or powered to study cure of HFS as the primary end point. Because the majority of surgeons performing MVD for HFS believe strongly about the use of intraoperative EMG, it is unlikely that a large prospective, randomized multicenter trial will be undertaken.…”

Intraoperative cranial nerve monitoring

“…30,33,42,60,65,83 Moller and Jannetta 60 reported the outcome of 67 consecutive patients who underwent MVD for hemifacial spasm with intraoperative monitoring of the LSR. Of the 44 patients in whom the LSR disap-peared during surgery, 42 were free from hemifacial spasm postoperatively.…”