Ultrasound Elastography Tracks Reversible Masseter Remodeling After BoNT-A Injections

Botulinum neurotoxin type A (BoNT-A) induces reversible changes in both masseter volume and elasticity, according to a new prospective study using ultrasound elastography (USE) to quantify structural adaptation post-injection. The findings, published ahead of print in Aesthetic Plastic Surgery, support USE as a non-invasive modality for monitoring treatment response and fibrosis risk in patients undergoing aesthetic jawline slimming.

The self-controlled study enrolled 14 participants (28 masseter muscles) aged 21 to 27 years. Investigators performed standardized ultrasound measurements—masseter thickness and shear wave velocity (V median)—at baseline and 1, 3, and 6 months following BoNT-A injection.

Significant reductions in masseter thickness were observed at 1 and 3 months post-treatment (mean decrease: 28.9%–31.5%; P ≤ .05), followed by partial volumetric recovery (47.4%) by month 6. Elasticity declined from 2.53 ± 0.46 m/s at baseline to 2.10 ± 0.45 m/s by month 3 (P ≤ .05), and then returned to baseline levels (2.70 ± 0.68 m/s; P > .05) by 6 months.

Interestingly, changes in thickness and elasticity were not correlated, suggesting that masseter atrophy and biomechanical recovery follow separate regenerative pathways. The study’s longitudinal design enabled clear differentiation between transient atrophy and potential fibrotic changes.

“BoNT-A induces transient masseter atrophy and elasticity reduction, with full elastic recovery by 6 months despite incomplete volume restoration,” the authors wrote. “USE effectively tracks reversible microstructural remodeling, distinguishing atrophy from fibrosis. These findings support USE as a tool for optimizing injection timing and monitoring functional recovery.”