CLINICAL HISTORY
A 81-year old male patient presented with left knee pain refractory to non-steroidal anti-inflammatory agents for 6 months. He did not describe night sweats, fever or weight loss. Family history and the rest of medical history were unremarkable. In physical examination, swelling and tenderness was prominent on proximal part of left tibia. Arthralgic gait was observed. The laboratory evaluation was remarkable for WBC: 14.200/mm3 with 95% neutrophils, erythrocyte sedimentation rate 98 mm/hr, and CRP 3.02 were found. In conventional knee X-Ray irregularity in cortex of left proximal tibia and decrease in bone density was seen (Figure 1A). Magnetic resonance imaging showed a large, heterogeneous contrast enhancing lesion involving the medullary and cortical bone of the proximal tibia with cortical disruption and extension into the adjacent soft tissue (Figure 1B). No evidence of lymphadenopathy, organomegaly, or other mass lesions can be found on physical examination and radiologic studies. Trucut biopsy was performed. Pathological examination revealed pleomorphic cells with large nuclei in fibrous background composed of small lymphoid cells among bone trabecules (Figure 2). These cells showed strong positivity with CD20 (Figure 3) while small lymphoid cells were CD3 positive. ALK and CD30 were negative. Bone marrow biopsy was normal.

Fig 1(A,B): Malignant lymphoma of the proximal tibia. (A): Anteroposterior radiograph shows a radiolucent osteolytic lesion. (B): Coronal T1-weighted image indicates involvement of bone marrow with low-intensity signal as well as involvement of surrounding tissues

Fig 2: Large pleomorphic cells on the fibrous background admixed with lymphoid cells (H&E;, x200)

Fig 3. Diffuse CD20 expression of large cells (x400)

What is your diagnosis?

PATHOLOGIC DIAGNOSIS
Primary diffuse large B cell lymphoma of bone

1) Durr HR, Muller PE, Hiller E, et al. Malignant lymphoma of bone. Arch Orthop Trauma Surg 2002;122:10-6.

2) Misgeld E, Wehmeier A,·Krömeke O; et al. Primary non- Hodgkin’s lymphoma of bone: three cases and a short review of the literature. Ann Hematol 2003;82:440-3.

3) Krishnan A, Shirkhoda A, Tehranzadeh J, et al. Primary bone lymphoma: radiographic-MR imaging correlation. Radiographics 2003;23:1371-83.

4) Rosai and Ackerman’s Surgical Pathology, 9th edition, Mosby 2004.