Lymphoma masquerading as Paget's disease of bone: a rare diagnostic challenge.

Paget's disease of bone (PDB) is a skeletal remodeling disorder diagnosed primarily via radiographs. In long bones, the early lytic stage of the disease is characterized by flame-shaped or blade of grass radiolucent bone resorption beginning in subchondral bone with variable length of extension into the metadiaphysis, and the later stages show bone expansion, cortical thickening, and coarsening of the trabeculae [1, 2]. Despite the usually diagnostic features, other considerations with overlapping appearance include aggressive benign and malignant bone tumors [3]. Malignancy such as lymphoma can present shared clinical features to PDB. When there is doubt as to the diagnosis, biopsy should be performed. A 60-year-old male presented with chronic left lower extremity pain. Radiographs showed a flame-shaped lytic lesion in the left femur with corresponding uptake on the bone scintigraphy. Radiographic features were suggestive of PDB, but due to some atypical findings, a biopsy was performed and showed small lymphocytic lymphoma (SLL) in the setting of chronic lymphocytic leukemia (CLL). This diagnosis led to the patient being promptly treated with targeted therapy and radiation. Pathologic verification is critical in an aberrant presentation of PDB to mitigate misdiagnosis and establish an appropriate therapeutic course.