Modelling the cryogenic treatment of warts and recommendations for changes to current clinical practice

Cryotherapy is a commonly used and recommended treatment for warts and there is wide variation in technique between clinicians applying the same mode of cryotherapy. To address this uncertainty in clinical practice a mathematical model is used to demonstrate the relationship between freezing time and tissue freezing zone for two commonly used cryogens (liquid nitrogen spray and nitrous oxide probes). It is found that nitrous oxide probes need substantially longer application time to obtain the same necrosis region as liquid nitrogen sprays. Overspray from liquid nitrogen spray is shown to lead to increased damage to healthy tissue surrounding a wart. Using a barrier of petrolatum (petroleum jelly) on the healthy tissue is demonstrated to be an effective means for limiting this damage. Changes to clinical practice to take account of these findings are recommended and need clinical trials to verify their applicability.