Mycosis fungoides presenting as symmetric concentric patches mimicking figurate erythema

EAC: erythema annulare centrifugum MF: mycosis fungoides TCR: T-cell receptor CASE REPORT A 52-year-old white male presented to outpatient dermatology clinic for evaluation of a 4-year history of a recurrent, intermittent rash that appeared as symmetrically distributed, red annular patches on nonesun-exposed areas of his trunk and extremities. The lesions gradually expanded in concentric rings with scale over several months. The affected areas were mildly pruritic, and he experienced arthralgias with each flare. His medical history was noncontributory, and his only medication was a proton pump inhibitor, which he had been taking for many years. At an outside facility, Lyme disease testing was negative, and he was given the initial clinical diagnosis of erythema annulare centrifugum (EAC) and was treated with topical and systemic corticosteroids, which provided only temporary improvement. On examination, the bilateral upper and lower extremities had pink-red, symmetric, concentric annular patches with trailing scale covering 10% to 15% of his body surface area (Fig 1). There was no palpable cervical or axillary lymphadenopathy. Clinically, the differential diagnosis included EAC, erythema gyratum repens, tinea corporis, and mycosis fungoides (MF). Results of laboratory investigations were within normal limits. A punch biopsy and a broad shave