Botulinum Toxin in Management of Limb Tremor

Essential tremor is characterized by persistent, usually bilateral and symmetric, postural or kinetic activation of agonist and antagonist muscles involving either the distal or proximal upper extremity. Quality of life is often affected and one's ability to perform daily tasks becomes impaired. Oral therapies, including propranolol and primidone, can be effective in the management of essential tremor, although adverse effects can limit their use and about 50% of individuals lack response to oral pharmacotherapy. Locally administered botulinum toxin injection has become increasingly useful in the management of essential tremor. Targeting of select muscles with botulinum toxin is an area of active research, and muscle selection has important implications for toxin dosing and functional outcomes. The use of anatomical landmarks with palpation, EMG guidance, electrical stimulation, and ultrasound has been studied as a technique for muscle localization in toxin injection. Earlier studies implemented a standard protocol for the injection of (predominantly) wrist flexors and extensors using palpation and EMG guidance. Targeting of muscles by selection of specific activators of tremor (tailored to each patient) using kinematic analysis might allow for improvement in efficacy, including functional outcomes. It is this individualized muscle selection and toxin dosing (requiring injection within various sites of a single muscle) that has allowed for success in the management of tremors.