| Summary: | We report the case of a 42-year-old woman with rheumatoid arthritis undergoing treatment with subcutaneous tocilizumab for the past 6 months. Three days after the administration, an asymptomatic inflammatory annular plaque of 4 cm with discrete whitish scales at the inner border margin developed at the injection site in the left iliac fossa. A smaller plaque in the left groin appeared soon after. The mycological exam was negative. Histology showed a lymphoplasmacytic superficial and deep perivascular, and periadnexal, dermal infiltrate, without epidermal changes. Lesions spontaneously regressed in 4 months. The diagnosis was clinically and histologically consistent with erythema annulare centrifugum, following the exclusion of other differential diagnoses. Erythema annulare centrifugum represents a delayed-type hypersensitivity reaction generally considered idiopathic or otherwise related to numerous triggers, including drugs such as biologics. We describe the first reported case of tocilizumab-induced erythema annulare centrifugum. This case should alert dermatologists to this relatively rare and complex entity and should raise awareness to cutaneous biologic drug reactions.
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