Papular urticaria

Papular urticaria

Cause

This term, with its hint that the condition is a variant of ordinary urticaria, is a misnomer. Papular urticaria is nothing more than an excessive, possibly allergic, reaction to insect bites. The source of the bites may be simple garden pests but more often is a parasite on a domestic pet. Human fleas are now rather uncommon. Often the source cannot be traced.

Presentation

Lesions are usually most common on the arms or legs. They consist of groups or lines of small itchy excoriated smooth urticarial papules (Fig. 15.1) of a uniform size that may become bullous and infected. Some clear to leave small scars or pigmented areas.

Course

Lesions tend to start after infancy, and an affected child will usually ‘grow out’ of the problem in a few years, even if the source of the bites is not dealt with. Individual lesions last for 1 or 2 weeks and recur in distinct crops, especially in the summerahence the lay term ‘heat bumps’. The lesions will disappear with any change of environment, for example by going on holiday. Surprisingly often only one member of a family is affected, perhaps because the others have developed immunological tolerance after repeated bites.

Complications

Itching leads to much discomfort and loss of sleep.

Impetiginization is common.

Differential diagnosis

The grouped excoriated papules of papular urticaria are quite different from the skin changes of scabies, in which burrows are the diagnostic feature. Atopic prurigo may be more difficult to distinguish but here there is usually a family history of atopy and frankly eczematous plaques are found in a typical distribution.

Investigations

The parents should be encouraged to act as detectives in their own environment, but some resist the idea that the lesions are caused by bites, asking why the other family members are not affected. This attitude is often supported by veterinarians who, after a superficial look at infested animals, pronounce them clear. In such cases the animal should be brushed vigorously while standing on a polythene sheet. Enough dandruff-like material can then be obtained to send to a reliable veterinary laboratory. Often the cause is a Cheyletiella mite infestation.

Treatment

Local treatment with Eurax HC ointment or calamine lotion, and the regular use of insect repellents, may be of some help but the ultimate solution is to trace the source of the bites.

Infested animals should be treated by a veterinar-ian, and insecticidal powders should be used for soft furnishings in the home. Sometimes professional exterminators are needed; but even measures such as these can meet with little success.