SIR, Many thanks are due to Deirdre Buckley and Anthony Du Vivier for their extremely comprehensive and informative review of the use of topical contact sensitizers. 1 I have been involved in a systematic review of randomized controlled trials for all local treatments for cutaneous warts; 2 during our searches we discovered two randomized controlled trials of dinitrochlorobenzene (DNCB) 3, 4 which were subsequently included in our review. Neither trial was mentioned in the review by Buckley and Du Vivier and both are worthy of comment. The trials were small (80 patients in total) and of relatively low quality but they have the advantage of being properly randomized and hence less prone to bias. Data pooled from these trials showed cure in 32 of 40 (80%) with active treatment and 15 of 40 (38%) with placebo, odds ratio 6Æ67 (95% confidence interval 2Æ44–18Æ23), random effects model.

There were no precise data concerning adverse effects in either of these trials but Rosado-Cancino et al. 3 commented that six of their 20 participants treated with DNCB sensitized only after the second application of 2% DNCB to the warts. All of these patients subsequently experienced significant local irritation, with or without blistering, when they were treated with 1% DNCB. None withdrew from the study. In our review, cryotherapy, interestingly, fared slightly less well than simple topical treatments containing salicylic acid, with much more substantial evidence for the efficacy of the latter than the former. Two trials (involving a total of 320 participants) comparing these two treatments showed them to be only of equivalent efficacy, with cure rates of approximately 60–70%. Of all the treatments reviewed, DNCB came out with the highest odds ratio for cure of warts, albeit with rather wide confidence intervals because of the small numbers in these two trials. We thought it reasonable to conclude, however, that topical immunotherapy with sensitizers such as DNCB appears to be one of the more promising therapeutic avenues for refractory warts.