Liquid nitrogen cryotherapy of common warts: cryo-spray vs. cotton wool bud

Background Viral warts represent a large workload for dermatology departments. Cryotherapy with liquid nitrogen is the most widely used method of treatment by dermatologists and is increasingly used by general practitioners in the U.K. Existing data relating to the response to cryotherapy are virtually all derived from the use of a cotton wool bud as the applicator. There is an increasing trend to use the cryo-spray to freeze warts and it has been assumed that this is equally effective. In view of the workload involved it is important to test this assumption. Objectives This prospective study was undertaken to compare these two methods of liquid nitrogen cryotherapy with regards to cure rate after 3 months of treatment. Methods Patients referred to two hospital dermatology departments with hand or foot warts were allocated to have liquid nitrogen applied with either a cryo-spray or with a cotton wool bud. Using either technique, liquid nitrogen was applied until ice-ball formation had spread from the centre to include a margin of 2 mm around each wart. Treatment was done fortnightly for up to 3 months. Plantar warts were pared and treated with a double freeze-thaw cycle. The endpoint of the study was complete clearance of all warts. Results Three hundred and sixty-three patients were enrolled, mean age 21 years (range 3-75), 188 male and 175 female. The mean duration of the warts was 98 weeks (median 78, range 2-936). The number of warts on the hands and feet varied from one to 80 (mean 5). The treatment groups were comparable with regards to baseline demographics. Two hundred and seven patients were evaluable. Cure rates at 3 months were 47% in the cotton wool bud group and 44% in the cryo-spray group (P = 0.8). Warts that had been present for 6 months or less (n = 31) had a greater chance of clearance (84%) compared with warts that had been present for more than 6 months (39%, n = 176) (P < 0.0005). Conclusions Cryotherapy with liquid nitrogen for hand and foot warts in our study was equally effective when applied with a cotton wool bud or by means of a spray.