Microwaves have radiofrequencies within the nonionizing electromagnetic spectrum, which includes infrared waves and longer radio waves. Microwaves have the ability to heat substances through a process termed diathermy, which has been used for decades to coagulate tissue during surgery. These waves are relatively selective, preferably heating tissues with high water content, such as glands, by taking advantage of the greater dipolarity of water molecules compared to fat. This property proved useful in AH by enabling the design of a device to penetrate to the deep layer of subcutaneous dermal tissue with wavelengths of 5.8GHz. At that level (2 and 5mm deep), eccrine and apocrine glands can be destroyed through thermolysis. Histology shows that they are then replaced by fibrosis.14 The device (miraDry; Miramar Labs, Sunnyvale, CA, USA) protects the dermis and epidermis by a combined system of suction and cooling of the skin. Suction facilitates uniform treatment and prevents surrounding tissues (e.g., nerve endings in the brachial plexus) from being harmed. Two reviews by Jacob2 and Johnson et al.15 treat these principles and mechanisms of action in greater detail.

The procedure can be summarized in 3 steps. First a template that is sized to match the surface of the axillary vault is placed on the skin to guide marking landmarks, which show where the device's handpiece will be placed in a later step (Fig. 1A). Second, tumescent anesthesia is applied to the area (Fig. 1B). The actual treatment is given in the third step, in which the tip of the handpiece is applied to release microwave energy at the previously marked points (Fig. 1C). The device has different treatment settings. The program automatically used for the upper part of the axilla, where the brachial plexus is close to the surface, is the lowest setting (level 1) to safeguard against accidental injury. The remaining area of the axilla can be treated at the maximum setting (level 5), especially if tumescent anesthesia has been provided. An area 10×30mm is treated each time the handpiece is applied. Thus, depending on the size of the axillary vault, between 12 and 39 applications will be made. Depending on what treatment level is used (higher levels require a longer session), the procedure lasts between 25 and 40minutes per axilla.

Figure 1.

A, Template marks placed before treatment. B, Application of tumescent anesthesia. C, Application of microwaves with the handheld device.

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The procedure is painful so local anesthesia must be provided. The templates also include points showing where the anesthetic should be injected. The number of injections ranges from 26 to 60 on each side, depending on the size of the axillary vault. Such a large number of infiltrations is also painful, even if an insulin or mesotherapy needle is used. Tumescent anesthesia is therefore preferred today. This safe technique is also applied in other clinical settings, including AH treated by curettage.12 A high volume–between 80 and 120mL, depending on the size of the vault–of a mixture of epinephrine and a 1% lidocaine solution in physiological saline is injected into each axilla. The procedure to provide tumescent anesthesia is practically painless and allows higher levels of microwave energy to be applied, making for greater efficacy. In addition, brachial plexus injury is less likely because the high volume of saline and anesthetic insulates the tissues. Finally, this technique uses less anesthetic than the initially recommended local anesthetic procedure.

Nearly all patients experience painful local inflammation and develop subcutaneous nodules (Fig. 2) that gradually disappear over the course of the first week. Also often observed is local bruising, a result of the suction applied. Oral anti-inflammatory medication is therefore routinely prescribed for the first 72hours, along with application of a cold pack. Discomfort can sometimes last several weeks or occasionally as long as 3 to 4 months, but without interfering with daily activities.

Figure 2.

Local inflammation and subcutaneous nodules after treatment.

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The only important complication described in the literature is neuropathy, reported in 2 cases. One patient had medial and cubital nerve damage that resolved fully by 12 months with rehabilitation.16 Paradoxically, that patient had been treated at the lowest energy setting and had received tumescent anesthesia, under optimal procedural conditions that usually safeguard against nerve damage. The other patient had neuropathy associated with muscle weakness, a clinical picture that resolved in 6 months.17

Compensatory hyperhidrosis seems to be a rare complication. It was reported in 2 patients, one of whom presented persistent facial sweating after the procedure.3 Finally, another possible complication is permanent hair loss, an effect that has been described in 26% of patients.17 This side effect has led to current interest in studying microwave therapy as a novel means of hair removal, especially for gray hair.

A few trials and case series have provided information on this newly available modality.3,14,17,18 Noteworthy was the randomized multicenter trial of Glaser et al.,3 who compared microwave treatments to sham treatments in 120 patients. Follow-up lasted 12 months in the treatment group of 81 patients. All enrolled individuals had scores of 3 or 4 on the Hyperhidrosis Disease Severity Scale (HDSS) (Table 1). Statistically significant improvement was observed 1 or 2 months after treatment in the active treatment group, where disease severity decreased in 89% of the patients (vs 54% in the sham-treatment group, P<.001). The effect difference was maintained at the 6-month follow-up. When the outcome measure of efficacy was a reduction of 2 or more points on the HDSS scale, 67% of patients in the active treatment group achieved success (vs 13% in the sham-treatment group). A similar degree of efficacy was maintained in the microwave-treated group at 12 months.

Ninety percent in a series of 31 patients showed improvement 12 months after microwave treatment (reaching HDSS scores of 1 or 2 from baseline scores of 3 or 4).17 Patient satisfaction with treatment was high in 90%. Finally, 83% of a series of 11 patients with both AH and bromhidrosis reported HDSS scores that were 2 points lower 7 months after treatment.14

Bromhidrosis–a problem that can appear along with AH or in isolation–is another promising new indication for this therapy because microwaves are able to eliminate apocrine glands. A substantial number of patients in the series analyzed by Hong et al.17 mentioned they perceived no unpleasant body odor after treatments. Similarly, 93.8% of the patients in the series of Lee et al.14 reported a good or excellent response of body odor to microwave therapy. Only certain surgical techniques19 or certain laser therapies (e.g., interstitial Nd:YAG 1444nm treatments20 have been able to offer a degree of relief to patients with this problem to date.

Cost is one of the most important problems of microwave therapy mainly because of the price of consumables and the time invested by staff who apply the treatments. No cost comparisons have been made between this modality and others, but we can calculate that 2 microwave sessions would cost as much as 6 BTX-A treatments priced around €500 per session. BTX-A has a mean duration of effect of 8 months. Therefore, the investment in microwave treatment will have paid for itself in about 4 years.