Prognostic value of intra-operative lateral spread response monitoring during microvascular decompression in patients with hemifacial spasm.

Hemifacial spasm (HFS) has characteristic and specific electrophysiological features, primarily the lateral spread response (LSR). The aim of this study was to evaluate the correlation between changes in the lateral spread response during microvascular decompression (MVD) and the clinical outcome after MVD. Seventy-two patients with HFS who were treated with MVD were included in this study. Intra-operative facial electromyography (EMG) was performed and brainstem auditory evoked potentials were monitored. In 32 (44.4%) patients, the LSR persisted after MVD. Among these 32 patients, 11 had mild HFS at discharge and six had mild HFS at the 6 month follow up. Out of the 40 patients in whom the LSR disappeared intra-operatively after MVD, five had mild HFS at discharge and four had mild HFS at the 6-moth follow up. The clinical outcome of HFS after MVD does not always correlate with intra-operative EMG abnormality. Therefore, the prognostic value of intra-operative LSR monitoring with respect to long-term results is questionable.