Annular Plaque on the Inner Thigh

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A 54-year-old woman presented with an extremely painful and pruritic lesion on the right thigh of 1-year duration. Her medical history was significant for systemic lupus erythematosus (for which she was currently on Hydroxychloroquine) and hidradenitis suppurativa. There was no significant family history. The lesion had initially been treated with oral terbinafine by her rheumatologist based on the clinical impression of tinea cruris. However, as the lesion continued to grow with significant scar tissue formation, the patient was referred to dermatology.
Physical examination revealed a well-demarcated tumor with a central hypopigmented atrophic plaque and an overlying hyperpigmented net-like scarring area. At the periphery, there was raised hyperkeratotic border surrounded by erythema (Fig. 1).
Histopathologic features of a small punch biopsy revealed a focally crateriform epidermal invagination (Fig. 2). The specimen also exhibited a dense superficial and deep perivascular and interstitial, plasma cell-rich infiltrate with some containing Dutcher bodies (Fig. 3) and pandermal fibrosis (Figs. 4, 5). Fite stain, Gomori methenamine silver stain, and Periodic acid–Schiff–diastase stain were negative. An additional elliptical biopsy, taken three weeks later, from the raised border revealed more prominent papillomatous endophytic and crateriform irregular epidermal hyperplasia, pandermal fibrosis, a moderate to dense superficial and mid perivascular and interstitial lymphoplasmacytic infiltrate with neutrophils, and extravasated erythrocytes. All special stains for microorganisms were negative again. Although Quantiferon-TB gold test was positive, chest x-ray and mycobacterial culture from tissue were negative. Additional workup for an infectious etiology (rapid plasma reagin test and tissue cultures for fungus) was consistently negative.
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