Should local anesthetics be banned during treatment of palmar hyperhidrosis with botulinum toxin A?Montreal University Hospital Center, Hôpital Saint-Luc, Montreal, Quebec. email@example.com
Antranik Benohanian MD
Dermatology Online Journal 13 (3): 33
I read with great interest the comments by Lim and Seet on the possible long-term effects of prolonged and repeated injections of local anesthetics and the permanent neurotoxicity that may result [1, 2].
Paracelsus, one of the pioneers of toxicological science, about 400 years ago, stated that there are no toxic materials, there are only toxic doses. The average lidocaine volume per spurt delivered through the needle free injector Med-Jet® MBX (manufactured by MIT Canada, a subsidiary of Medical International Technology USA) prior to the injection of botulinum toxin type A (BTX-A) with needle is 0.02 mL per site [3, 4, 5]. Assuming that 40-50 such sites are to be injected per hand, the total volume will hardly exceed 1 ml. This is in agreement with the recommendations brought up by the authors of the referenced article by Lim and Seet as follows: "other than using the lowest possible concentration and dosage of local anesthetics, no other option is currently available to prevent local-anesthetic induced direct neurotoxicity" . Further, this volume of 1 ml of lidocaine is much less than that used in a traditional nerve block, the latter being 5 to 6 times more.
Although not recommended by the manufacturer, reconstitution of BTX-A in lidocaine, originally published by Gassner , started to gain popularity when two other studies confirmed that toxin potency is not affected [7, 8]. Based on the results of their study, Vadoud-Seyedi and Simonart concluded that reconstitution of BTX-An in lidocaine jeopardizes neither the short-term nor the long-term results achieved with BTX-A in the treatment of axillary hyperhidrosis (HH) . Moreover, they even recommend that the procedure be evaluated for patients with palmar and plantar HH to eventually replace peripheral nerve blockade . However, the authors did not elaborate how they would deliver the diluted BTX-A through the densely innervated dermis of the palm where eutectic mixtures of local anesthetics such as Emla® fail to control the pain caused by the needle prick during BTX-A injection. One valid option would be through needle free lidocaine injection (jet anesthesia). The injectate, delivered through the MED-JET® is directed through a small orifice about four times smaller than a 30 G needle. As most of the pain occurs during the piercing of the skin itself, the smaller the orifice the better the pain control will be. The high speed penetration during jet anesthesia is another factor contributing to the reduction of pain. The amount of pain generated by jet anesthesia is no more than that induced by an elastic band snapped against the palmar skin. Conversely, lidocaine injected with a needle will not be of any help to relieve the pain during the needle prick itself.
Similarly, Alam et al. found that the use of preservative-containing saline to reconstitute BTX-A can significantly decrease patient discomfort on injection . The preservative used was benzyl alcohol, which, besides having anesthetic properties, may also prolong the stability of the product with refrigeration for 5 weeks. Their work was based on facial skin.
In my practice, I have found that BTX-A injections, topical aluminum chloride formulations  and iontophoresis, when used in combination, may act synergistically to (a) reduce the BTX-A dose and (b) extend the interval between BTX-A injections beyond the 3-month period mentioned by Lim and Seet . Low BTX-A doses together with longer intervals between their injections not only lower the treatment cost but may also prevent antibody formation that neutralizes the effect of BTX-A .
Even though cryo-analgesia is considered by many to be a useful technique to inject BTX-A for palmar HH, difficulty is encountered when the diluted BTX-A is injected into frozen tissues , this will need a wait of 2-3 seconds per site in order that the tissue warms up before injecting the drug. This is not an issue with jet anesthesia, which, when delivered through an appropriate device, remains one of the convenient ways to treat palmar HH. The technique can be viewed at http://www.benohanian.com/multimedia/AVSEQ02_1.wmv.
Dimache et al. reported that jet injectors can be safely used in the medical practice if they are protected by the sterile anticontaminant disposable device . The Med Jet MBX is now equipped with a sterile disposable anticontaminant nozzle, easily replaced within a few seconds, that may allow treatment of more than one patient without necessarily undergoing a thorough sterilization of the equipment.
There is no perfect, completely painless and risk-free treatment for palmar hyperhidrosis. Luckily, as a recent article in Therapy shows , there are now more options available than in the last century. It is important to constantly review what scientific information is available on each approach to ensure the most appropriate choice in each case.
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2. Lim EC, Seet RC. Another injection-free method to effect analgesia when injecting botulinum toxin for palmar hyperhidrosis: cryoanalgesia. Dermatol Online J. 2007 May 1;13(2):25.
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