A Prospective Randomised Double-Blind Dose-Comparative Clinical Investigation Evaluating Skin Mechanical Property Alterations after Botulinum Toxin Type a Injections for the Treatment of Forehead Rhytides

Background: Few insights into the skin mechanical properties have been carried out, whilst the clinical evidence after interrupting the cholinergic system in human skin still remains unclear.

Objectives: We prospectively investigated the skin mechanical properties alterations in patients who received intramuscular injections of botulinum toxin A (BTX-A) for forehead rhytides and compared two injection doses.

Methods: Of the forty-two patients enrolled, half randomly received intramuscular injection with 2 units (group I) and half with 4 units (group II) of BTX-A in each injection point. The baseline and post-treatment skin mechanical parameters including gross elasticity (R2), net elasticity (R5), viscoelastic ratio (R6) and biological elasticity (R7) were measured using the Cutometer^® and compared.

Results: Treatment with BTX-A provided overall significant skin mechanical property alterations at the injection site of both treatment groups during the 16 weeks period without any significantly statistical difference between both groups. Significant decreases in biological elasticity, net elasticity and viscoelasticity properties were observed at 2 weeks follow-up and started to recover since that time. All the skin mechanical properties recovered to baseline level at 16 weeks of follow-up for both dosage groups, indicating that a higher dosage (4-units) did not conduct a longer duration until relapse when compared with the 2-unit dosage.

Conclusions: We concluded that intramuscular injection of BTX-A will significantly regulate the gross elasticity, net elasticity, functional elasticity and viscoelastic elasticity at injection point at a radius of 1.5 cm at 2 weeks, 4 weeks and 8 weeks follow-up. The potency relapsed at 16 weeks follow-up.