Bite-sized advice for busy GPs
Many patients do not expect freezing of warts to hurt beyond the initial discomfort. But this is not usually the case you should warn them that cryotherapy will burn the skin and the area will feel like any other burn for several days. They should also be warned that blistering may occur.
Thick scale and keratin crusting will reduce the effect of cryotherapy and should be removed before treatment to increase the chances of success.
Cryotherapy may be used for the treatment of basal cell carcinomas, but there is a high incidence of recurrence and no histological proof of diagnosis or cure, so it should probably not be used for BCCs in the primary care setting. For similar reasons, cryotherapy should not be used for moles.
Cryotherapy may cause scarring, resulting in hair loss in affected areas or deformity of nails when used around the matrix. The risk of scarring is directly proportional to the degree
Cold may penetrate deep below the surface of the skin, affecting structures such as nerves and tendons. Care should always be taken in vulnerable areas, such as over the head of the fibula (common peroneal nerve), the elbow (ulnar nerve) and the lateral palmar aspect of the fingers (palmar digital nerve).
Permanent hypo- or depigmentation may occur following cryotherapy. This is especially important when treating people with black or brown skins who may be happy to be rid of their wart, but not at the cost of permanent hypopigmented patches. Only use cryotherapy on the faces of these patients as a last resort.
If cryotherapy is considered for the lower limbs, always consider the risk of poor healing and ulceration, especially in people with peripheral vascular disease. This is especially relevant when using cryotherapy to treat Bowen's disease.
Manipulation of the skin overlying tendons, and also spraying the aerosol at an oblique angle rather than vertically, may reduce the risk of tendon damage in at-risk areas.
Aerosol cryotherapy agents are available OTC for the treatment of viral warts, but these only produce temperatures of -50°C against -196°C achievable with liquid nitrogen. This makes them less effective, but with less risk of tissue damage
Inflammation after cryotherapy is thought to be prostaglandin mediated. If necessary, topical clobetasol cream and oral aspirin may help.
Nigel Stollery is a GP and dermatological clinical assistant in Kibworth, Leicestershire