Treatment of Essential Vocal Tremor: A Scoping Review of Evidence-Based Therapeutic Modalities

Abstract

Essential vocal tremor (EVT) is an uncommon but challenging condition to manage. Several medical and interventional treatment options have been reported but efficacy remains unclear. We performed a scoping review of high-quality clinical trials to identify effective evidence-based treatments for EVT. Scoping review. Relevant studies were identified using the databases MedLine, Cochrane Central Register of Controlled Trials, and Embase. Subjective and objective outcomes for each modality were analyzed and the effect sizes were quantified using Hedges' g measure to allow comparison between studies. We identified 421 studies eligible for screening with 11 included in the final analysis. Evidence supporting effective EVT treatments was found for bilateral versus unilateral deep brain stimulation (DBS) (Hedges' g 0.65, 95% CI = 0.10-1.20) and octanoic acid (Hedges' g 1.15, 95% CI = 0.40-1.90). Evidence to support the use of methazolamide was not sufficient (Hedges' g 0.51, 95% CI = -0.64 to 1.66). Botulinum toxin (BT) injections were equivalent when comparing unilateral versus bilateral (Hedges' g -0.18, 95% CI = -1.06 to 0.70); BT did not display any advantage over propranolol (Hedges' g -0.47, 95% CI = -1.73 to 0.78) or injection augmentation (Hedges' g 0.068, 95% CI = -0.98 to 1.12). Our review finds very little high-quality evidence supporting any treatment for EVT. Octanoic acid reduced fluctuations in EVT but did not affect the perception of the tremor. In refractory cases, bilateral DBS was superior to unilateral DBS in improving subjective voice outcomes. Unilateral and bilateral BT injections were equivalent, and BT injection was not more effective than injection augmentation. Further direct comparison in well-designed prospective studies may help clarify optimal treatment for EVT patients.