Effect of transdermal botulinum toxin on sweat secretion in subjects with idiopathic palmar hyperhidrosis

SIR, We explored whether a simple unassisted transdermal delivery of botulinum toxin type A (BTX) is effective for treating palmar hyperhidrosis. Palmar hyperhidrosis is common and troublesome. Nonsurgical treatments include topical antiperspirants, iontophoresis, anticholinergic drugs and botulinum toxin injections. Most antiperspirants contain 1–2% aluminium salts and, although convenient and effective, require repeated application and can irritate skin. Iontophoresis, although effective, has disadvantages of requiring frequent, lengthy treatment and potential skin allergy. Oral anticholinergic drugs are largely ineffective because of undesirable side-effects. BTX injections are highly effective in treating palmar hyperhidrosis with effects lasting 6 months. However, pain associated with injection is a major limitation. Surgical procedures such as thoracic sympathectomy are fairly effective but high rates of compensatory hyperhidrosis are a major negative side-effect. We have previously postulated that BTX can be administered topically, either with or without assistance by procedures such as iontophoresis or sonophoresis. This prospective study was performed at the National University Hospital, Singapore. Informed consent was obtained from 16 subjects aged 20–50 years with idiopathic palmar hyperhidrosis. The hospital ethics board reviewed and approved the study. Exclusion criteria were diabetes mellitus, polyneuropathy, anticholinergic medication, pregnancy and thyrotoxicosis. Caffeinated substances were withheld 6 h prior to testing. Subjects received 100 units of BTX (Botox ; Allergan, Irvine, CA, U.S.A.) in saline solution transdermally on the right (dominant) hand, heated with a thermal lamp before testing to achieve maximal opening of sweat pores and thus permit better BTX entry. Saline solution served as a control to the left hand. Tight-fitting powder-free plastic gloves were worn and the fluid was carefully squirted into the palmar glove side along the inside of the sleeve and the wrist tied off to prevent leakage. Gloves were worn for 2 h and subjects instructed to rub the palms to maximize BTX absorption. Sweat production was assessed using the Quantitative Sweat Measurement System (Q-Sweat; WR Medical Electronics Co., Stillwater, MN, U.S.A.) and the starch–iodine sweat test. Assessments were made 1 h prior to BTX application and at weeks 2, 4, 8, 16 and 24 following BTX application. Q-Sweat parameters included baseline sweat volume and percentage increase in poststimulation sweat volume. The starch–iodine sweat test rated sweating on a scale of 1–3: 1, sweating absent; 2, 50% sweating; 3, 80% or more sweating. Patients rated their hand sweating prior to BTX application and at weekly intervals for the first 2 months followed by monthly intervals for the remaining 4 months. Patient Sweat Scoring, subjective sweat assessment, used an analogue scale of 0–100 points: 0, no sweating; 100, most severe form of sweating. Sweat output parameters were compared between BTX and saline solution. Both subjective and objective parameters of sweat production collected from all 16 patients showed this technique of delivering BTX through the skin not to be effective. There was no statistically significant improvement (P > 0Æ01; Mann–Whitney test) at 2 and 24 weeks post-treatment in all subjects (Fig. 1).