Epidermal spongiotic Langerhans cell collections, but not eosinophils, are a clue to the diagnosis of allergic contact dermatitis: A series of 170 clinically- and patch test-confirmed cases

Background: Allergic contact dermatitis cannot be reliably differentiated from other forms of spongiotic/eczematous dermatitis by histology alone. Textbooks and recent studies have variably supported the specificity of dermal eosinophils, eosinophilic spongiosis, and Langerhans cell collections, among other features. Objective: To assess which histopathologic features favor a diagnosis of allergic contact dermatitis. Methods: In this case control study with prospective validation, patients were evaluated by patch testing and skin biopsy. Lesional histopathologic features were independently assessed. Results: One hundred seventy cases fulfilled inclusion criteria. Langerhans cell collections were more likely to be found in allergic contact dermatitis (29/111, 26%) (P = .03). Heavy dermal eosinophilic infiltration was associated with diagnoses other than allergic contact dermatitis. No significant differences were found for any other predictor variables. Limitations: Mostly retrospective study with small validation sample. Conclusion: This largest study to date is the first to independently confirm Langerhans cell collections as the single histopathologic feature most closely associated with allergic contact dermatitis.