Nummular eczema and contact allergy: a retrospective study.

Etiopathogenesis of nummular eczema is obscure; many causative factors have been proposed. Only a few studies investigated the relevance of contact allergy. This retrospective study aimed to investigate the role of contact allergy in the underlying mechanism of nummular eczema. From the 29,323 consecutive patients, we patch-tested for eczematous dermatitis of various type, 1022 (3.5%) with nummular eczema were enrolled. Data were collected for each patient, including age, sex, occupation, symptoms onset and duration, onset and spread sites, and clinical evidence or history of atopy. Histological analyses of acute phase lesions were carried out in some patients. Peak incidence of age at disease onset was found in the third decade of life. Predominant sites of lesions were upper (75.8%) and lower (64.5%) limbs, followed by trunk, dorsum of the hands, and face and neck. Three hundred thirty-two (32.5%) of 1022 patients showed positive reactions to 1 or more allergens. Highest sensitization rates were found with nickel sulfate (10.2%), potassium dichromate (7.3%), and cobalt chloride (6.1%). Histopathology showed less pronounced spongiosis in atopic subjects and the elderly. Because this study demonstrates that contact allergy is common with nummular eczema, patch testing is strongly advisable in every patient with persistent nummular dermatitis.