Quantification of the efficacy of botulinum toxin type A by digital image analysis

Background. Botulinum toxin type A (BT-A) is increasingly being used by der matologists for correction of frown lines. Because objective measurements o f clinical results appear to be difficult, several different treatment prot ocols have been issued purely empirically or on the basis of subjective rat ings. Objective. Our purpose was to establish objective parameters to measure the efficacy of BT-A for correction of hyperkinetic facial lines. Methods: Thirty consecutive patients received BT-A injections for correctio n of facial expression lines. For each patient a full range of facial expre ssions was recorded by means of a digital imaging system that allowed ident ical positioning and illumination before and after treatment. Computer-assi sted measurements of brow mobility were used to measure muscular paralysis. Results: Reproducibility of serial photographs by means of a digital overla y technique, vas confirmed by 4 independent observers. Upward mobility of b rows was decreased to 35% at 2 weeks and 71% at 12 weeks after treatment. I n contrast, inward mobility (frowning) was decreased to 7% at 2 weeks and 5 7% at 12 weeks. Brow-to-brow distance in repose increased with treatment by 13% and displayed a negative correlation with age. Conclusion: The effects of BT-A on upper face muscular activity can reprodu cibly be measured by digital image analysis; this is a valuable tool for cl inical documentation and evaluation of treatment efficacy. Onset and offset of the effects of BT-A display a longer time course than previously assume d. Tissue qualities such as elasticity contribute measurably to smoothing f acial expression lines after BT-A treatment and correlate inversely with ag e.