Background: Local injections of botulinum toxin type A (BTX-A) have been used successfully to treat focal hyperhidrosis, but because experimental data were lacking, doses have been chosen arbitrarily or empirically.
Objectives: To analyse dose dependency and duration of BTX-A-derived suppression of sweat gland activity.
Methods: Employing a standardized scheme (four injections, square 2 x 2 cm), different doses of BTX-A [Dysport(R); 2.5-120 mouse units (MU)] were injected subcutaneously at the lateral aspects of both of the lower legs in 15 healthy volunteers. Sweat tests were performed before, and 3 weeks and 6 months after, BTX-A injections. Sweating was visualized by staining with iodine starch, and quantified by capacitance hygrometry after carbachol iontophoresis, the quantitative sudomotor axon reflex test (QSART).
Results: Iodine starch staining indicated a threshold dose of 10 MU (2.5 MU cm-2) leading to visible anhidrotic skin spots after 3 weeks in all subjects. This was maintained for 6 months with doses of 50 MU (12.5 MU cm-2) or higher, but the size of the anhidrotic skin area decreased over time (P < 0.001) indicating partial recovery at the edges. After 3 weeks QSART was significantly reduced (P < 0.02) and completely suppressed by doses of 80 MU (20 MU cm-2) or more, although after 6 months QSART increased again to pre-BTX-A levels (P < 0.001). Both methods indicated that the suppression of sweating is dose dependent (QSART: r = -0.70, P < 0.001; iodine starch staining: r = 0.74, P < 0.001).
Conclusions: Our findings suggest that BTX-A effectiveness can be quantified by testing sudomotor function. For the first time threshold doses for the suppression of sweating have been defined.