242 Lepromatous Leprosy Mimicking Cutaneous B-Cell Lymphoma: A Diagnostic Pitfall

Introduction/Objective Lepromatous leprosy (LL) is a chronic infection caused by Mycobacterium leprae and can present with a variety of morphologic patterns. Histologically, it may overlap with cutaneous lymphoproliferative disorders such as cutaneous B-cell lymphoma (CBCL), particularly when it presents as a dense dermal lymphoid infiltrate, potentially leading to diagnostic error. Methods/Case Report A 73-year-old female presented with multiple erythematous scaly patches on her face and torso. The clinical impression suspected a lymphoproliferative disorder. Skin biopsy revealed a dense, nodular lymphohistiocytic infiltrate with a mixture of T and B lymphocytes. Molecular studies showed a kappa light chain gene rearrangement suggestive of CBCL. However, Fite-Faraco staining revealed numerous acid-fast bacilli (AFB) within macrophages, leading to a diagnosis of lepromatous leprosy. Results NA Conclusion LL may histologically mimic CBCL, especially when the dermal infiltrate is lymphocyte-predominant and accompanied by clonal gene rearrangement. However, a key distinguishing feature is the presence of intracellular bacilli, identifiable by acid-fast staining. Misdiagnosis may result in inappropriate treatment and delayed initiation of effective therapy. This case highlights the importance of including infectious etiologies such as LL in the differential diagnosis of dense dermal lymphoid infiltrates. Special stains, clinicopathologic correlation, and a high index of suspicion are essential for accurate diagnosis and appropriate management.