Abstract

An 84-year-old gentleman with a history of chronic lymphocytic leukemia/small lymphocytic lymphoma was referred for suspected cutaneous T-cell lymphoma (CTCL). His clinical photographs revealed red-brown papules with background erythema on the extremities and the submitted clinical impression was eczematous dermatitis versus CTCL. He also reported numbness in his distal extremities attributed to ibrutinib. Skin biopsy showed a superficial and deep periappendageal, perineural, and interstitial infiltrate of numerous lymphocytes, histiocytes forming loose microgranulomas, and plasma cells. Lymphocytes were CD3-positive and displayed slightly enlarged, hyperchromatic, irregular nuclei and limited tagging of the dermal-epidermal junction. T-cell clonality studies were positive for clonal rearrangement of TRG and TRB. In addition, examination of IGH and IGK revealed a clonal B-cell population. These results prompted referral for possible granulomatous mycosis fungoides. Additional immunohistochemical stains demonstrated that the epidermotropic lymphocytes were positive for CD8, TIA-1, and TCR-beta F1 with diminished CD7 expression. Because of the granulomatous nature of the infiltrate and the prominent inflammation of neurovascular bundles, special stains for microorganisms were also performed. Fite and Ziehl-Neelsen stains revealed numerous acid-fast bacilli within nerves and histiocytes, diagnostic of leprosy. While false-positive gene rearrangement studies have been reported in inflammatory conditions, it is a less well recognized phenomenon in the setting of infection. This case reinforces that, despite immunophenotypic aberrancies and identification of a clonal T-cell population, infection should be excluded before a diagnosis of granulomatous mycosis fungoides is rendered.

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