Localization modalities for botulinum neurotoxin injection

Botulinum toxin is a targeted therapeutic that acts primarily at the site of injection. Various approaches have been taken to guide injection into the selected muscle, gland, organ or other body area. Guidance methodologies that can be used in the office setting for skeletal muscle and salivary gland percutaneous injection include uninstrumented manual needle placement, electromyography (EMG), electromyography with electrical stimulation (e-stim), ultrasound (US) and combined guidance (US + EMG or US + e-stim). This article reviews the advantages, disadvantages, and accuracy of each method and the impact of each guidance technique on therapeutic outcome for muscle and salivary gland injections. Overall, manual placement may suffice for large and superficial muscles, however, all instrumented techniques improve accuracy. Electromyography can uniquely provide information on muscle activity, while e-stim can aid injection in patients who cannot voluntarily activate a selected muscle. Ultrasound is the only technique that can visualize internal structures, allowing identification of a safe trajectory for injection of small or deep targets that might otherwise be inaccessible.