Treatment of recalcitrant plantar hyperhidrosis with type-A botulinum toxin injections and aluminum chloride in salicylic
acid gelMontreal University Hospital Center, Hôpital Saint-Luc, Montreal, Quebec. firstname.lastname@example.org
Dermatology Online Journal 14 (2): 5
Case 1—a 32-year-old man was first seen on October 20, 2003 for a disabling plantar hyperhidrosis (HH) and bromhidrosis (BH) from which he suffered since his adolescence. Topical application of 55 percent aluminum chloride hexahydrate (AC) in 6 percent salicylic acid (SA) gel for a period of four weeks did not improve his HH. On November 3rd 2003, he was injected with Botulinum Toxin Type A (BTX-A, Botox® Allergan Pharmaceuticals, Irvine, California) at a dose of 200 mouse units (mu) per sole. Anesthesia was achieved through the nerve block technique. The patient had difficulty walking for several hours after this technique. Because the plantar HH did not improve a month after the injections, instead of resorting at still higher doses, topical 55 percent AC in 6 percent SA gel was resumed and the plantar HH and BH were brought under control within days. The initial application was nightly, reduced later to once a week or less.
Case 2—an 18 year-old woman was first seen on November 15, 2005 because of her recalcitrant plantar HH. Topical application of 55 percent AC in 6 percent SA gel for a period of 4 weeks failed to provide improvement. On January 16, 2007, the patient was treated with 150 mu of BTX-A per sole on both feet. Needle-free anesthesia was used as the analgesic method [1, 2, 3]. Because BTX-A injections proved to be inadequate to control plantar HH a month after their administration, 55 percent AC in 6 percent SA gel was resumed and within days HH became under control. The gel application was initially once daily, and was later tapered down to once every 7-10 days.
Botulinum toxin type A is known to be a safe and effective treatment for axillary and palmar hyperhidrosis [4, 5], but little is known about its effect on plantar hyperhidrosis or its appropriate dosage. Although 100 mu may seem an adequate dose for the palm, plantar hyperhidrosis requires much higher doses. Few reports exist in the literature describing the adequate dose of BTX-A per sole. Recommended doses vary from 50 to 250 mu of BTX-A per sole [6, 7, 8]. I found that the average dose of BTX-A per sole is closer to 200 mu. Even at these high doses, the results of BTX-A injections may still be inadequate, forcing the clinician to either increase the dose, add a topical medication and iontophoresis or resort to surgery. The risk of antibody formation may also increase with these high doses [9, 10, 11].
Lowe et al.  suggested that when BTX-A injections alone fail to control palmar hyperhidrosis, the addition of topical aluminum chloride could provide more efficacy. The use of aluminum chloride in salicylic acid gel may enhance even further this efficacy [12, 13]. Knowledgeable pharmacists are capable of preparing extemporaneous formulations, ranging from 15 to 55 percent aluminum chloride in a hydroalcoholic gel containing 2-6 percent salicylic acid tailored to patient's tolerance and need. It is of note that although both patients failed to respond to 55 percent aluminum chloride in 6 percent salicylic acid gel and BTX-A injections when used alone, they responded with a successful outcome when these regimens were combined. Aluminum chloride in salicylic acid gel offers the following advantages in the treatment of palmoplantar hyperhidrosis:
- It may be used as a first line therapy for palmar and plantar hyperhidrosis because alcohol gel is better tolerated than an alcohol solution. The rationale of using SA in the gel vehicle is to enhance the penetration of AC through the thick horny layer present on the palms and soles and, having antiperspirant properties of its own, it could act synergistically with AC to enhance its antiperspirant effect. Moreover, although AC is soluble 1 in 1 in water, it is only soluble 1 in 4 in ethanol. In this extemporaneous gel vehicle, AC is dispersed in the form of microcrystals, and could reach supersaturated concentrations of up to 55 percent [12, 13].
- It may be used as adjunct treatment to iontophoresis when iontophoresis alone fails to control HH.
- It may be used as an adjunct treatment to BTX-A when BTX-A alone fails to show any improvement of palmar or plantar HH, a month after its injection.
- It may be used to extend the interval between BTX-A injections, especially when the effect of BTX-A starts to fade. High doses of BTX-A, coupled with shorter intervals between injections have the potential of inducing neutralizing antibodies which render BTX-A injections totally ineffective [9, 10, 11].
It is also worthwhile mentioning that case # 1 did not like the nerve block method prior to BTX-A injections because he was not able to walk for several hours after this treatment. It was fortunate that BTX-A injections were no longer needed because he was still under control with a maintenance treatment of his topical 55 percent AC gel once every 10 days when last contacted. Case # 2 had needleless anesthesia with a needle-free device (Med-Jet MBX® ) and had no difficulty walking after her BTX-A injections. She was satisfied with the needle-free anesthesia technique and would return for re-injection with BTX-A as needed.
Although, technically it would be possible to inject BTX-A directly into the dermis through the needle free device, this method was not favored for fear of partial denaturation of BTX-A that could occur with the violent agitation during its injection. Naumann et al. , when comparing BTX-A injection for focal HH through Dermojet® versus needle, found that needle injection was much more effective in reducing hyperhidrosis. Nevertheless, direct BTX-A injection through the needle free device may be used in the needle phobic patient. In the last three years I have used needle free lidocaine anesthesia, instead of the traditional nerve block, prior to BTX-A injection with needle to circumvent the potential complications of the nerve block. One study confirmed that BTX-A potency is not affected by the presence of lidocaine  and even suggested to reconstitute the toxin in lidocaine instead of unpreserved saline. Also, the availability of anticontaminant disposable devices  that take a few seconds to change between patients, allows the treatment of more than one patient in a same setting before sterilizing the needle-free device. The modified Bier block  is one good alternative to provide anesthesia prior to BTX-A injection with a needle.
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