Botulinum Toxin in Parkinson's Disease Tremor: A Critical Evaluation of the Evidence and Clinical Practice.

Approximately 30% of patients with tremor-dominant Parkinson's disease (PD) have rest tremor that persists despite optimal dopaminergic therapy. When deep brain stimulation and focused ultrasound are unavailable or declined, the therapeutic options narrow. Botulinum toxin (BoNT) offers a targeted, titratable, reversible approach, but whether a peripheral neuromuscular blocking agent makes sense for a centrally generated tremor is a legitimate question that deserves a direct answer. This narrative critical review appraises what is currently known across PD and non-PD tremor conditions, defines the technical requirements for safe and effective injection, and provides a practical framework for patient selection and clinical management. The PD-specific literature rests on a single positive double-blind randomized controlled trial of 30 patients; all remaining data are open-label or extrapolated from other tremor conditions, and this narrative synthesis combines heterogeneous conditions, outcome scales, and toxin protocols. A recurring technical observation is that, in the available trials, individualized, EMG-guided injection has been associated with substantially lower rates of hand weakness than fixed-dose injection (reported reductions from roughly 30-70% to below 15%) while maintaining tremor reduction, although the degree of benefit and weakness risk vary with the tremor syndrome, injected muscles, baseline impairment, dose, and guidance method. The careful patient selection this approach requires helps the individual clinician and patient achieve tremor relief, but it departs from the unselected real-world PD population and introduces selection bias that makes a large, statistically representative cohort difficult to assemble. In well-selected patients at centers with the appropriate expertise, BoNT may be a clinically useful option, but routine adoption is not yet supported.