Longitudinal Assessment of Masseter Muscle Elasticity Changes After BoNT-A Injection Using Ultrasound Elastography: A...

Area of Science:

• Muscle physiology
• Medical aesthetics
• Diagnostic imaging

Background:

• Botulinum neurotoxin type A (BoNT-A) injections are common for masseter hypertrophy.
• Long-term structural changes and fibrosis risk in masseter muscles post-BoNT-A are not fully understood.
• Ultrasound elastography (USE) is a non-invasive tool for assessing muscle elasticity and fibrosis.

Purpose of the Study:

• To investigate the long-term microstructural effects of BoNT-A on masseter muscles.
• To evaluate the utility of ultrasound elastography (USE) in monitoring these changes.
• To assess the reversibility of masseter muscle remodeling after BoNT-A treatment.

Main Methods:

• A prospective self-controlled trial involving 14 participants (28 masseter muscles).
• Measurements of masseter thickness and USE (shear wave velocity, V median) at baseline and 1, 3, and 6 months post-injection.
• Statistical analysis using paired t-tests and Spearman correlation.

Main Results:

• Masseter thickness significantly decreased (28.9-31.5%) at 1-3 months, with partial recovery by 6 months.
• Muscle elasticity (V median) decreased at 1-3 months but returned to baseline by 6 months, indicating reversible adaptation.
• Changes in muscle thickness and elasticity were uncorrelated, suggesting distinct recovery pathways.

Conclusions:

• BoNT-A induces transient masseter muscle atrophy and reduced elasticity.
• Full elastic recovery occurs by 6 months, while volume restoration is incomplete.
• USE is effective in tracking reversible microstructural remodeling and differentiating atrophy from fibrosis, aiding treatment monitoring.