Botulinum Toxin Efficacy in Upper Limb Tremor: A Systematic Review and Meta-Analysis.

[BACKGROUND] Essential tremor (ET) and dystonic tremor syndrome (DTS) can be treated using botulinum toxin (BoNT) injections. Previous reviews lacked an assessment of the certainty of evidence and focused solely on clinician-reported outcomes. Additionally, studies have demonstrated interindividual variability in BoNT efficacy.

[OBJECTIVE] The aim of the study was to assess the efficacy and safety of BoNT injections for ET and DTS of the upper limbs, and to identify factors associated with BoNT efficacy.

[METHODS] We systematically searched Pubmed, Embase, Cochrane Library, and Web of Science databases for studies on BoNT injections in ET and DTS of the upper limbs. The certainty of evidence was rated using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach. Outcomes from randomized controlled trials (RCTs) were pooled as standardized mean differences (SMDs).

[RESULTS] We identified 5 RCTs, 6 open-label trials, and 6 retrospective cohort studies. Meta-analysis of post-intervention scores showed a moderate effect on patient-reported change (SMD: 0.58 [95% confidence interval [CI]: 0.39, 0.78]), no effect on clinically rated tremor severity (SMD: 1.69 [95% CI: -3.80, 0.42]), and no effect on grip strength (SMD: -0.63 [95% CI: -1.37, 0.10]). In contrast, meta-analysis using change-from-baseline scores showed an improvement of clinically rated tremor severity (SMD: -1.12 [95% CI: -1.70, -0.54]). Certainty of evidence ranged from low to very low. No clear associations between BoNT efficacy and tremor phenotypes or injection strategies were identified.

[CONCLUSIONS] Patient-tailored BoNT injections may be effective and safe for ET and DTS. More trials are needed to confirm efficacy and safety, identify which tremor phenotypes benefit the most, and optimize injection strategies.