Another Great Imitator: Allergic Contact Dermatitis Differential Diagnosis, Clues to Diagnosis, Histopathology, and Treatment

Allergic contact dermatitis (ACD) is a type IV (delayed) hypersensitivity reaction that has a wide spectrum of presentations that often imitate or overlap with other cutaneous eruptions. Differential diagnoses to consider include infections, skin lymphoma-malignancies, inflammatory dermatoses, nutritional deficiencies, and mechanical causes of tissue damage. We discuss clues to the diagnosis of ACD, such as pruritus, localization to the area of skin contact with the allergen, recurrence with repeat exposures, and supportive skin biopsy histology. Epicutaneous patch testing remains the gold standard for diagnosing ACD. Definitive treatment is contact allergen avoidance and, when indicated, dietary restriction. With these measures, most patients will improve clinically. In cases where avoidance measures and interim topical therapies fail, ultraviolet light therapy or systemic immunosuppression may be considered. Key points 1. Allergic contact dermatitis (ACD) is a type IV (delayed) hypersensitivity reaction with a range of clinical presentations. 2. Mimickers of ACD include infections, skin lymphoma-malignancies, inflammatory dermatoses, nutritional deficiencies, and mechanical causes of tissue damage. 3. Allergen avoidance, which might include dietary restriction, is the definitive treatment for ACD.