Background: A quantitative numerical method for assessing the extent and duration of the inhibitory action of botulinum neurotoxin type A on mimetic muscles would potentially enable more detailed evaluation of the overall efficacy of this aesthetic treatment.
Aim: To evaluate skin displacement analysis (SDA) as a tool for assessment of the extent and duration of effect of incobotulinumtoxinA on mimetic muscles in the glabellar region in routine daily practice.
Methods: A total dose of 30 U incobotulinumtoxinA was injected into the fronto-glabellar region of 16 subjects. SDA was performed at baseline and during onset and recovery from incobotulinumtoxinA treatment at various timepoints up to 24 weeks after treatment. The reference point for SDA was located at the upper margin of the eyebrow, 30 mm lateral to the median line. To correlate and validate SDA results, semi-quantitative wrinkle score assessments were performed in parallel.
Results: At baseline, the mean horizontal skin displacement was 5.4 mm (standard deviation: ± 1.4 mm). During onset of action after treatment, skin displacement values decreased from baseline (100%) by 46%, 85%, and 90% at day 2, week 1, and week 2, respectively. During recovery from incobotulinumtoxinA action, skin displacement values increased to 33%, 50%, and 93% of the baseline value at 6, 12, and 24 weeks after treatment, respectively. The inhibitory effect of incobotulinumtoxinA was highly variable among subjects, ranging from 25% to 68% of the baseline value 12 weeks after treatment. Overall agreement between SDA values and wrinkle scores was good.
Conclusion: SDA represents a novel, objective method for the quantitative evaluation of the effect of incobotulinumtoxinA on mimetic muscles underlying the fronto-glabellar region, and showed good correlation with wrinkle score assessments. Both SDA and wrinkle score indicated the persistence of treatment effects 24 weeks after injection.