Treating Plantar Warts with Local Anaesthetic Infiltration - A Cautionary Tale.
Microwave therapy, using the Swift® unit, has become a mainstream treatment in the management of verrucae showing immunomodulatory effects at a cellular level and good clinical clearance rates . The data from the most recent post-marketing survey of 126 clinics covering over 8600 treatments in adults concurs with these findings [data submitted for publication]. For some patients however, the discomfort of the treatment, has led to the use of local anaesthesia by some practitioners. In a very few cases treated in this way, ulceration has been the result even when using standard energy protocols.
Even as a rare event it is interesting to uncover why the use of local anaesthesia may increase the risk of ulceration for these patients. A paper from the respected Journal of the European Academy of Dermatology and Venereology  may give some insight into this phenomenon. Published in 2015, the paper was a retrospective review of 53 patients who underwent Nd:YAG laser treatment for recalcitrant plantar warts. Of the 53 respondents, 10 were given local anaesthesia using local infiltration. Consequently, 4 patients in this group [n=40%] went on to develop tissue breakdown/ulceration whilst none of the other 43 patients undergoing treatment without local anaesthetic developed this complication. The Nd:YAG laser, like microwave, produces a rapid heating of tissues to bring about resolution. However, unlike microwave, this may be a direct destructive effect rather than by immunomodulation.
When examining the patients undergoing treatment using local anaesthetic, all received anaesthesia with lidocaine via local infiltration. The authors of this paper suggest that subcutaneous lidocaine collected in the subcutaneous tissues below the wart and consequently when the laser was applied, the collection of anaesthetic was superheated heated causing tissue damage and breakdown. Their second theory suggests that the acidity of the lidocaine may have also played a part but this perhaps, was difficult to explain how it may have led to tissue loss. As a result of these findings, the authors of the study latterly administered anaesthesia remotely from the wart - as a peripheral nerve block. Subsequently, no patients suffered ulceration as a result, but as the authors state more data is required to confirm this.
So, what can be learned from this work? Firstly, that local infiltration with local anaesthetic potential risks tissue breakdown when using heat-based energies even when standard treatment energy protocols are used. Consequently, practitioners should avoid using this technique, perhaps employing a remote nerve block to reduce the chances of ulceration or consider adopting a lower energy regime when using local infiltration of anaesthesia before treatment of warts. Of course, prospective data collected in due course will corroborate these changes in methods of application but hopefully, the overall effect will be to reduce the risk of ulceration to a minimum for patients.
1. Bristow IR, Lim W, Lee A, Holbrook D, Savelyeva N, Thomson P, Webb C, Polak ME, Ardern-Jones MR: Microwave therapy for cutaneous human papilloma virus infection. Eur J Dermatol 2017, 27(5):511-518.
2. Smith EA, Patel SB, Whiteley MS: Evaluating the success of Nd: YAG laser ablation in the treatment of recalcitrant verruca plantaris and a cautionary note about local anaesthesia on the plantar aspect of the foot. J Eur Acad Dermatol Venereol 2015, 29(3):463-467.