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Background <p>Botulinum neurotoxin type A (BoNT-A) is widely used to treat masseter hypertrophy, but its long-term structural effects remain unclear. While animal studies suggest reversible and irreversible remodeling, human data on microstructural changes are limited. Ultrasound elastography (USE) offers a non-invasive method to quantitatively assess muscle elasticity and detect fibrosis risk.</p> Methods <p>A prospective self-controlled trial enrolled 14 subjects (28 masseter muscles) aged 21–27 years. Masseter thickness and standardized USE measurements (shear wave velocity, V median) were performed at baseline and 1, 3, and 6&#xa0;months post-injection. Statistical analysis included paired t-tests and Spearman correlation.</p> Results <p>Masseter thickness decreased significantly by 28.9–31.5% at 1–3 months (<i>p</i> ≤ 0.05), with partial recovery (47.4%) by 6 months. V median (elasticity) declined at 1–3 months (2.53&#xa0;±&#xa0;0.46&#xa0;m/s to 2.10&#xa0;±&#xa0;0.45 m/s, <i>p</i>&#xa0;≤&#xa0;0.05), but returned to baseline by 6&#xa0;months (2.70&#xa0;±&#xa0;0.68&#xa0;m/s, <i>p</i>&#xa0;&gt; 0.05), indicating reversible structural adaptation. Thickness and elasticity changes were uncorrelated, suggesting distinct recovery mechanism.</p> Conclusion <p>BoNT-A induces transient masseter atrophy and elasticity reduction, with full elastic recovery by 6 months despite incomplete volume restoration. 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.</p> Level of Evidence II <p>This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors <a href="http://www.springer.com/00266">www.springer.com/00266</a>.</p>

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Longitudinal Assessment of Masseter Muscle Elasticity Changes After BoNT-A Injection Using Ultrasound Elastography: A Prospective Self-Controlled Study

  • 期刊论文

  • 发表日期：

    2025年12月1日

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  • Mengyue Yan,
  • Yuna Luo,
  • Qian Wu,
  • Minghao Zhao,
  • Yuzhi Qiu,
  • Hongli Chai,
  • Ying Jia,
  • Panxi Yu,
  • Jianjian Lu

摘要

Background

Botulinum neurotoxin type A (BoNT-A) is widely used to treat masseter hypertrophy, but its long-term structural effects remain unclear. While animal studies suggest reversible and irreversible remodeling, human data on microstructural changes are limited. Ultrasound elastography (USE) offers a non-invasive method to quantitatively assess muscle elasticity and detect fibrosis risk.

Methods

A prospective self-controlled trial enrolled 14 subjects (28 masseter muscles) aged 21–27 years. Masseter thickness and standardized USE measurements (shear wave velocity, V median) were performed at baseline and 1, 3, and 6 months post-injection. Statistical analysis included paired t-tests and Spearman correlation.

Results

Masseter thickness decreased significantly by 28.9–31.5% at 1–3 months (p ≤ 0.05), with partial recovery (47.4%) by 6 months. V median (elasticity) declined at 1–3 months (2.53 ± 0.46 m/s to 2.10 ± 0.45 m/s, p ≤ 0.05), but returned to baseline by 6 months (2.70 ± 0.68 m/s, p > 0.05), indicating reversible structural adaptation. Thickness and elasticity changes were uncorrelated, suggesting distinct recovery mechanism.

Conclusion

BoNT-A induces transient masseter atrophy and elasticity reduction, with full elastic recovery by 6 months despite incomplete volume restoration. 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.

Level of Evidence II

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.