Defining urticarial dermatitis: a subset of dermal hypersensitivity reaction pattern.

BACKGROUND Urticarial dermatitis may represent a useful term for a subset of a reaction pattern designated most commonly as dermal hypersensitivity by pathologists. The term is not commonly used, and requires definition to determine whether it is clinically relevant. OBJECTIVES To define urticarial dermatitis and distinguish it from other urticarial reaction patterns and to review the frequency with which dermatologists can recognize clinical settings that match the biopsy findings of urticarial dermatitis. DESIGN Retrospective analysis of clinical and/or histological diagnosis of urticarial dermatitis, applying strict histological criteria in a center using urticarial dermatitis as a diagnostic term in 190 archived reports. SETTING Tertiary referral dermatopathology service reporting for dermatological practices in Sydney, Australia. MAIN OUTCOME MEASURES The correlation between clinical and histological diagnoses of urticarial dermatitis and alternate diagnoses was analyzed. The frequency of positive immunofluorescence findings for bullous pemphigoid was determined in a subset of patients with urticarial dermatitis in whom this test was ordered to exclude prodromal bullous pemphigoid. RESULTS Urticarial dermatitis was the histological diagnosis in at least 1 biopsy result in 148 patients, and matched the provisional clinical diagnosis in 49 (33.1%) patients. Urticarial dermatitis was the only diagnosis provided in 21 patients. The main alternate clinical diagnoses provided were early bullous pemphigoid or dermatitis herpetiformis (47 patients [31.8%]), dermatitis (39 patients [26.4%]), drug reaction (35 patients [23.6%]), urticarial vasculitis (24 patients [16.2%]), and urticaria (12 patients [8.1%]). In 91 patients with a clinical diagnosis of urticarial dermatitis, the histological diagnosis in at least 1 biopsy result was matched in 49 patients (53.8%); other histological diagnoses included dermatitis (21 patients [23.1%]), papular urticaria (12 patients [13.2%]), drug reaction (6 patients [6.6%]), and urticaria (3 patients [3.3%]). Review of 38 direct immunofluorescent results for prodromal bullous pemphigoid and a biopsy finding of urticarial dermatitis revealed only 3 positive results (7.9%). CONCLUSIONS Urticarial dermatitis seems to be a useful histological and clinical term for a subset of the dermal hypersensitivity reaction pattern. Although the clinical presentation is not restricted to a specific entity, eczema and drug reactions seem to be the most frequent clinical associations; and in a subset of patients, urticarial dermatitis remains as a recognizable reaction pattern. Urticarial dermatitis without eosinophilic spongiosis is not a reliable indicator for bullous pemphigoid, because the findings of immunofluorescence are often negative.