The Effect of Micro-Focused Ultrasound Treatment on Intradermal Botulinum Toxin Type A Injection

Botulinum toxin type A (BoNT-A) injection and micro-focused ultrasound with visualization (MFU-V) are becoming increasingly popular for various esthetic conditions. However, performing MFU-V subsequently to BoNT-A injection may diminish the efficacy of BoNT-A. Previous reports have indicated the impact of various energy-based devices on BoNT-A. Nevertheless, the influence of MFU-V on BoNT-A has yet to be investigated. Thus, this study aims to evaluate the effect of MFU-V on BoNT-A injection and to determine the optimal interval between each treatment. A randomized controlled study was conducted on 15 subjects. Each participant was assigned to receive four sites of intradermal BoNT-A injection on their forehead. Following BoNT-A injection, these locations were randomized to receive either no MFU-V treatment or further treatment with MFU-V (superficial transducer, 10.0 MHz, 1.5 mm) on the same day, Day 7, or Day 14. On Day 28 following injection, the anhidrosis area was measured using the iodine starch test to objectively evaluate the result. In comparison to the control site (1.10 cm²), the anhidrotic area was significantly smaller in all MFU-V treated sites (0.74 cm² in immediate MFU-V treatment, <i>p</i> < 0.001; 0.90 cm² in MFU-V Day 7, <i>p</i> = 0.005; 0.93 cm² in MFU-V Day 14, <i>p</i> = 0.021). There were no serious and esthetic complications reported in our study. <b>In conclusion,</b> MFU-V with a superficial depth transducer significantly reduced the efficacy of intradermal BoNT-A injection, especially within two weeks following BoNT-A injection. After BoNT-A injection, we recommend MFU-V treatment should be avoided for at least two weeks. Further study is required to evaluate the optimal interval between these two treatments.