PracticalDermatology

Multiple methods for improving patient comfort during botulinum toxin injections for hyperhidrosis have been implemented and reported in the literature, including nerve blocks, anesthetic creams, or cooling methods involving ice packs, ethyl chloride spray, or cold air devices, such as a Zimmer.^1-3 Nerve blocks have shown to be particularly effective for palmar and plantar injections. However, this method is invasive, requires precise technique, and involves the risk of nerve injury.1 In addition to the latency period required to achieve anesthesia, topical anesthetic creams only reach a limited level of anesthesia.^2-3 Lidocaine/prilocaine 2.5%-2.5% (EMLA) cream has been shown in separate studies to provide inferior local anesthesia in comparison to skin cooling with either ethyl chloride spray alone or ice application alone immediately prior to injections for botulinum toxin treatments involving the forehead and palmar areas.^2-3 Cryotherapy with liquid nitrogen is an often-overlooked skin cooling anesthetic option for botulinum toxin injections. Liquid nitrogen is easily accessible in most dermatologist offices without requiring the purchase of extra supplies. It is noninvasive, and there is no latency period prior to producing an anesthetic effect.

Liquid nitrogen cryotherapy is a cornerstone therapeutic instrument in dermatology for a number of conditions.4 The liquefied gas reaches a temperature of -196° Celsius (-321° Fahrenheit) as it freezes and destroys skin lesions while producing a mild stinging sensation and sometimes a blister.4 The technique used to destroy these lesions varies depending on the condition being treated in terms of the time of freeze-thaw cycles, margins, number of sessions, and length of intervals between treatments.4 To achieve these therapeutic outcomes, different techniques of freezing are utilized, but typically the spray of liquid nitrogen is administered at a 90° angle to the skin in close approximation from about 1-2cm away, thereby freezing the localized skin along with the associated margins, which subsequently turn a white color.4 When held at a distance of 8-10cm from the skin, the spray’s freezing effect on a very local area of skin is diminished to a cooling effect on a larger surface area (Figure 1).

Figure 1. Demonstration of cryotherapy method being utilized for anesthesia immediately prior to botulinum toxin injections to the palm for palmar hyperhidrosis.

A couple of seconds before the surgeon is about to start the injection procedure, an assistant can start spraying the liquid nitrogen in the treatment area and should continue in the path that the surgeon will follow. The endpoint of the liquid nitrogen spray is to provide cooling and anesthesia, and it should not be held in the same place long enough to cause frosting. An anesthetic effect similar to that resulting from ice pack application, ethyl chloride spray, or a Zimmer cold air device is produced from this cooling sensation. We have used this technique repeatedly in all skin types with no residual side effects, and specifically, no post-inflammatory pigmentary changes.

When used from this extended distance from the skin, liquid nitrogen cryotherapy can be utilized to safely and can effectively alleviate pain associated with botulinum toxin injections for hyperhidrosis. This method is underutilized and has not been previously described in the literature, despite its effectiveness, ease, and the superiority and practicality of cooling methods in comparison to nerve blocks and anesthetic creams.

Neither author has any relevant financial conflicts of interest to disclose.

1. Solomon P. Modified Bier block anesthetic technique is safe for office use for botulinum A toxin treatment of palmar and plantar hyperhidrosis. Dermatology online journal. 2007;13(3).

2. Alsantali A. A comparative trial of ice application versus EMLA cream in alleviation of pain during botulinum toxin injections for palmar hyperhidrosis. Clinical, cosmetic, and investigational dermatology. 2018;11:137.

3. Irkoren S, Ozkan HS, Karaca H. A clinical comparison of EMLA cream and ethyl chloride spray application for pain relief of forehead botulinum toxin injection. Annals of plastic surgery. 2015 Sep 1;75(3):272-4.

4. Cranwell WC, Sinclair R. Optimising Cryosurgery Technique. Australian Family Physician. 2017 May;46(5):270-4.