Abstract: 【Abstract】 Objective To investigate changes in thickness of the skin and muscular layer during the treatment with botulinum toxin A injections in patients with glabellar lines. Methods Twenty-six subjects with moderate to severe glabellar lines were enrolled into this study, who received botulinum toxin A injections in Peking Union Medical College Hospital from August 2017 to February 2018. Before the injections, 4 and 16 weeks after the injections, thickness of the dermis at the injection site was measured by using 50 MHz high-frequency ultrasound, and full thickness of the skin and thickness of the muscular layer were measured with 20 MHz high-frequency ultrasound. Repeated measures analysis of variance, paired t-test and Bonferroni method were used to compare the pretreatment and posttreatment tissue thicknesses measured by using high-frequency ultrasound. Results Before the injections, the thickness of the dermis, full thickness of the skin, thickness of the muscular layer were 2.01 ± 0.48, 4.32 ± 0.73 and 4.51 ± 0.67 mm respectively. No significant difference was observed among the pretreatment, 4- and 16-week posttreatment thickness of the dermis （F = 1.94, P = 0.199）, while there were significant differences among the pretreatment, 4- and 16-week posttreatment full thickness of the skin and thickness of the muscular layer （F = 6.28, 24.19, P = 0.020, < 0.001 respectively）. Four weeks after the injections, the full thickness of the skin significantly increased （4.88 ± 0.93 mm, t = 3.72, P = 0.004）, while the thickness of the muscular layer significantly decreased （3.82 ± 0.79 mm, t = 4.65, P = 0.001）compared with the pretreatment thicknesses. Sixteen weeks after the injections, the full thickness of the skin （4.61 ± 0.73 mm） and thickness of the muscular layer （4.38 ± 0.90 mm） did not significantly differ from those before and 4 weeks after the injections （all P > 0.0167）. Conclusions Botulinum toxin A injections can change the thickness of the subcutaneous tissue and muscular layer. High-frequency ultrasound can be applied to the evaluation of efficacy and follow-up after the treatment of glabellar lines with botulinum toxin A injections.

Key words: Ultrasonography, Botulinum toxins, type A, Dermis, Subcutaneous tissue, Muscular layer, Glabellar lines, High-frequency ultrasound, Skin thickness