[Round Table: urticaria with a physical cause]

Abstract

Physical urticaria comprises a series of clinically differentiated conditions in which wheals develop as a result of physical stimuli: mechanical (friction, pressure), cold, heat, increased body temperature, exercise exposure to sunlight, vibration and contact with water. The present study reviews their clinical, diagnostic and treatment characteristics. Although the precise prevalence of physical urticaria is not know, it nevertheless represents the most common form of urticaria of known etiology in children. Symptomatic dermatographism is the most frequent presentation in children; it may be present from birth and persist indefinitely. In order to study the prevalence of dermatographism in our pediatric population, we randomly selected 238 children of both sexes (128 boys and 110 girls) aged 2 to 14 years, in the Paternal Health Care Center (Valencia, Spain). An evaluation was made of skin response 5 minutes after the application of pressure (3,200 g/cm2) along a 5-cm extent of skin on the back, using a dermatographometer. A positive response was considered when a wheal over 2 mm in diameter developed; in this context, the prevalence of dermatographism was 24%, with a significant predominance of females (33%) over males (16%). According to the data obtained from the anamnesis, 41% of the children with dermatographism referred exanthema in response to friction and pressure compatible with symptomatic dermatographism, versus only 5% of those who tested negatively. Lastly, 42% of the children with dermatographism referred intense local reaction (5 cm or more) in response to mosquito bites, versus only 16% of the children who tested negatively for dermatographism. The study of bronchial reactivity to metacholine in 17 children with dermatographism but no bronchial asthma (based on the Chatham method) proved positive in 13 cases (76%). Seven of these 17 children (41%) yielded positive skin tests (3 referred symptoms of rhinitis, with no manifestations of asthma in any case), and the metacholine challenge proved positive in 5 (71%). Ten of the children showed negative skin testing for aeroallergens - with positive metacholine testing in 8 (80%). These results indicate a high prevalence of bronchial hyper-responsiveness in children with dermatographism, suggesting the existence of an association between skin and bronchial hyper-reactivity. Skin tests with aeroallergens were made in 45 of the 58 children with positive dermatographism; 38% were found to be positive for at least one of the allergens studied, a figure that increased to 43% when only considering children over the age of 7 years. This points to a high prevalence of atopy among children with dermatographism. In order to evaluate the prevalence of dermatographism in the atopic population, we studied 100 patients in the 4-14 years age range suffering from respiratory pathology associated with sensitization to aeroallergens. A positive response to pressure (3,200 g/cm2) was observed in 47% of cases, this being significantly higher than the prevalence observed among the general pediatric population.