Objective: To describe the outcomes of a new electromyography (EMG)-guided botulinum toxin (BT) clinic for treatment of tremor in our center.

Background: Tremor is often encountered in Movement Disorder practice, with essential tremor (ET) and Parkinson’s disease tremor (PDT) being the most common. Up to 60% of ET and PDT have inadequate response to medications^1,2. BT is an effective therapy for medication-refractory tremor³.

Method: A new EMG-guided BT clinic was set up in Aug 2024. The indication for referral to the clinic was medication-refractory or -intolerant upper limb tremor. BT injections were performed by 2 trained movement disorder specialists. All patients received onabobotulinum toxin A. The Fahn-Tolosa-Marin Tremor Rating Scale (TRS) was performed at baseline. Patients were asked to rate subjective improvement in tremor on a scale of 0 to 100%, with 0% indicating no improvement and 100% indicating tremor resolution.

Results: From Aug 2024 to Sep 2025, 22 patients were seen. Eighteen patients received BT injections under electromyography guidance. Muscles were selected based on clinical assessment. Of those who received BT injections, the baseline TRS was 21.3±8.4. Eleven (61.1%) were male. The mean age was 68.4±7.0 years. Nine patients had essential tremor (ET), 7 had PDT, 1 had dystonic tremor, and 1 had neuropathic tremor. The most commonly injected muscles were pronator teres, pronator quadratus, and supinator. The mean BT dose was 35.0±13.6U at the initial visit and 56.8±20.1U at the last visit. Overall, 12 (66.6%) reported any improvement in tremor, while 5 reported no improvement (data was missing for 1). Mean subjective improvement in tremor was 34.3±32.4% at last follow up. Improvement rates differed significantly across tremor types (ET 100% vs PDT 28.6% vs other tremor types 100%; Fisher’s exact test, p = 0.003). The most common side effect was finger weakness (N=4), which was temporary in all who developed it.

Conclusion: EMG-guided BT injection is a feasible therapeutic option for medication-refractory upper limb tremor. In contrast to existing reports³, our cohort showed varying response to BT injection amongst the different tremor types. This may be due to higher amplitude of PDT than other tremors, requiring higher doses of BT, or because PDT has rest, action and postural components and it can be challenging to determine which aspect is most bothersome to patients.

References: 1. Louis ED. Clinical practice. Essential tremor. N Engl J Med. 2001;345(12):887-891. doi:10.1056/NEJMcp010928
2. Zach H, Dirkx MF, Roth D, Pasman JW, Bloem BR, Helmich RC. Dopamine-responsive and dopamine-resistant resting tremor in Parkinson disease. Neurology. 2020;95(11):e1461-e1470. doi:10.1212/WNL.0000000000010316
3. Bellows S, Jankovic J. Botulinum Toxin for the Treatment of Tremors. Toxins (Basel). 2025;17(8):401. Published 2025 Aug 11. doi:10.3390/toxins17080401

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