Ultrasound visualization of Botulinum toxin injection: Identifying clinical correlates to optimize outcomes in spasticity management.

Background: Botulinum toxin injections are well established and commonly used for spasticity management. Clinicians strive to optimize outcomes from toxin injections. One potential complication is toxin spread beyond the intended muscle, which can lead to unwanted weakness. The utilization of ultrasound allows direct visualization of target muscles and identification of toxin leakage from the target muscle. Ultrasound evaluation of clinical factors that correlate to toxin leakage have not been studied.

Objective: To identify cases of botulinum toxin injectate leak beyond the targeted muscle during ultrasound-guided spasticity injections and associate cases of leak with predictive clinical factors, which include muscle size, fibroadipose changes, and number of previous injections.

Design: This was a prospective observational study.

Setting: An outpatient clinic in an academic medical center.

Patients: Patients who demonstrated wrist flexor spasticity warranting intervention were invited to participate.

Interventions: Patients received standard-of-care spasticity management with injection of onabotulinumtoxinA into the flexor carpi radialis muscle based upon clinical presentation and prescribing guidelines. Ultrasound video was recorded, and a blinded review was conducted by the study team.

Main outcome measures: The primary outcome measure was visualized leak of injectate on recorded ultrasound video. Documented leak was then associated with clinical factors including diameter of the flexor carpi radialis, volume of injectate used, history of prior injections, and fibrotic change of the muscle.

Outcomes: The study included 54 patients, 77.8% of whom had an underlying diagnosis of cerebrovascular accident. Injectate leak was observed in 18.5% of injections and could not be confirmed in 9.3% of injections. Multivariable analysis demonstrated increased odds of leak with higher Modified Heckmatt Scale score. No statistically significant increase in leak was noted with higher volume of injectate or smaller muscle diameter.

Conclusion: Extramuscular leak of botulinum toxin injection may be associated with fibroadipose muscle change.