Rare Case of Primary Bone Lymphoma.

Primary bone lymphoma (PBL) is a rare entity defined as a lymphoid neoplasm of bone that occurs in the bone without involvement of lymph nodes or other extranodal sites. In this report, we present a case of an elderly female with PBL who presented with regional lymphadenopathy and cutaneous lesions mimicking the primary cutaneous diffuse B-cell lymphoma (PCDBCL), leg type. This review describes the case of a 73-year-old female with primary bone lymphoma who presented with cutaneous lesions and regional lymphadenopathy. She was initially diagnosed with Paget's disease of bone but ultimately presented to the emergency room with a pathologic fracture of the left tibia and painful overlying cutaneous lesions. Imaging studies, including X-ray and computed tomography (CT) scans, along with a tibial biopsy, revealed findings consistent with PBL, characterized by large lymphoid cells that were positive for CD10, CD20, and Bcl6, with a high Ki-67 index. The diagnosis was confirmed despite the atypical cutaneous involvement. Due to her age, low-performance status, and extranodal disease, the patient was classified as high-intermediate risk according to the National Comprehensive Cancer Network International Prognostic Index (NCCN-IPI) criteria. The presence of extranodal involvement also placed her at intermediate risk for central nervous system (CNS) disease. The clinical presentation of PBLs is often nonspecific, and diagnostic criteria noted in the literature vary, making for a difficult diagnosis in clinical practice. To our knowledge, this patient is the first documented case of PBL with concurrent cutaneous manifestations and regional lymph node involvement. This case report and literature review investigate the possibility of PBLs presenting with lesions extending beyond the initial area of bony involvement.