The glabella tap reflex reveals fluctuations in the hyperexcitability of the facial nucleus with hemifacial spasm: a prospective observational study

Abstract

Background: The etiology of hemifacial spasm (HFS) remains controversial, with both peripheral and central mechanisms proposed. This study investigates the glabella tap reflex in HFS patients, exploring its relationship with facial nucleus hyperexcitability to assess its potential as a clinical marker of central pathophysiological fluctuations.

Methods: We prospectively enrolled a consecutive cohort of 69 patients with drug-refractory HFS who underwent microvascular decompression (MVD). Preoperative facial motor responses, including glabella tap-induced lateral spread and blink reflex, were assessed and recorded using standardized high-definition video. The latencies of these responses were compared using the Wilcoxon matched-pairs signed-rank test, and the correlation was assessed using Spearman analysis.

Results: Mechanical tapping of the unilateral glabella elicited simultaneous contraction of the orbicularis oculi and orbicularis oris muscles and simple blink reflex in HFS patients. No statistically significant difference was found between the latencies (p = 0.873). However, Spearman analysis revealed a moderate, statistically significant positive correlation between these two latencies (r = 0.563, p < 0.001).

Conclusion: The characteristics of the glabella tap reflex observed in HFS patients, particularly the variability in its manifestation, appear to reflect fluctuations in facial motor nucleus hyperexcitability. This reflex may serve as a readily accessible clinical marker for these dynamic central excitability states and potentially provide insights into pathways reconciling peripheral and central theories of HFS pathogenesis.

Keywords: Blink reflex; Facial nucleus hyperexcitability; Glabella tap reflex; Hemifacial spasm; Microvascular decompression.