Is the pre-operative lateral spread response on facial electromyography a valid diagnostic tool for hemifacial spasm?

The lateral spread response (LSR) on preoperative facial electromyogram (EMG) is a useful tool in evaluating patients with hemifacial spasm (HFS). There may be some instances where the LSR does not appear on the preoperative EMG, thus disrupting the diagnosis and treatment of HFS. In this study, we evaluated the patients who did not exhibit LSR on preoperative EMG but underwent microvascular decompression (MVD) for hemifacial spasm. We searched for patients who underwent MVD for HFS but had an absence of LSR on preoperative EMG between January 2016 and June 2018. Surgical outcomes were evaluated at 1, 3, and 6 months after surgery. Follow-up facial EMG was performed 3 months after surgery. Results were divided into two categories: (1) spasm relief within 24 h of surgery and (2) spasm was observed immediately post-operation. The following parameters were analyzed when comparing between the two groups: age, sex, affected side, duration of symptoms, and offending vessel(s). A total of 306 patients underwent MVD for HFS during the study period. Among them, 13 (4.2%) patients had no LSR on preoperative EMG. Eight patients (61.5%) were female and five patients were male. The 13 patients had a mean age of 51 years. All patients exhibited probable offending vessels in the root exit zone (REZ) of the facial nerve on preoperative magnetic resonance (MR) imaging that was confirmed during surgery. Seven patients were free of HFS immediately after surgery, though six patients were not. Only one (7.7%) patient had persisted symptom 6 months after surgery. No patients experienced recurrence of spasm, nor exhibited abnormal waves on follow-up facial EMG. LSR on facial EMG is a valuable tool for evaluating hemifacial spasm. However, although LSR did not appear on preoperative EMG, if the patient presents with typical symptoms and the offending vessels are identified on MRI, we expect good results after MVD for HFS.