Teaching Case

A 58 year, female with history of SLE under medication presented to the emergency department with complaints of excruciating knee pain radiating to thigh. She reported similar pain about a week back for which she attended the emergency department and was given pain medications, after which the pain subsided. No history of trauma was given. The patient was referred for emergency ultrasound to rule out DVT or ruptured baker’s cyst. X-ray pelvis was done to rule out avascular femoral necrosis.

X-ray pelvis was within normal limits. Ultrasound of right knee was negative for baker’s cyst or DVT with small amount of suprapatellar knee joint effusion and medial extrusion of the body of medial meniscus. Since the severity of pain was out of proportion to the imaging findings, MRI was advised.

MRI with contrast showed a long segment of diffuse marrow disease appearing T1 hypointense, T2/STIR hyperintense with heterogeneous contrast enhancement involving the proximal & mid shaft of femur with surrounding enhancing periosteal edema and nodular extra-osseous soft tissue component exhibiting restricted diffusion. Small focal areas of endosteal erosion in the posterior cortex of proximal femoral shaft. However, no frank cortical breach was seen.  A small similar area of marrow signal abnormality was noted in the right intertrochanteric region.

PET CT was done which showed multifocal areas of increased uptake involving the bilateral femurs, angle of right mandible, left glenoid, left 9^th rib, L2, L4 and L5 vertebral bodies, left pubis & left iliac bone. No significant regional lymph nodal disease noted.

A USG guided biopsy was performed of the soft tissue component adjacent to the right femur. Histopathological diagnosis of diffuse large B cell lymphoma (DLBCL) was given.

Background

Lymphoma represents a relatively well-recognized malignant phenomenon associated with lupus.[1]. Primary bone lymphoma is a rare extranodal presentation of non-Hodgkin’s lymphoma. Primary bone diffuse large B-cell lymphoma (DLBCL) is the most common pathological type, comprising about 80% of PBL.[2]A study examining predictors of increased lymphoma risk in systemic lupus suggested a potential role of cyclophosphamide and high cumulative steroid use. [3]

Clinical Perspective

Fever, adenopathy, weight loss are shared clinical features in SLE-related lymphoma and infections complicating SLE. Bone pain & swelling are the most common presenting symptoms of PBL. However, these features are not typical of lymphoma and can be associated with other marrow infiltrative etiologies. Therefore, a thorough assessment of the duration and chronicity of symptoms, exhaustive exclusion of other potential etiologies, and examination of tissue and bone marrow biopsies are essential in arriving at the right diagnosis. [4, 5] 

Imaging Perspective

MR imaging feature that is suggestive of infiltrative processes such as PBL is the replacement of bone marrow, especially in the setting of near-normal radiographic findings. Another and even more specific feature of round cell tumours such as lymphoma is the relatively minimal cortical destruction in the presence of extensive soft tissue and marrow involvement. Observation of these two factors in patients with suspected bone lymphoma will add a further degree of certainty to the diagnosis. FDG-PET exhibits increased uptake and demonstrates other areas of involvement. CT scan is helpful in evaluating erosion and biopsy guidance.  Lastly, the consideration of lymphoma in the appropriate differential diagnosis is important to ensure that an adequate biopsy sample be obtained for immunophenotyping and other analysis. [6]

Take-Home Message / Teaching Points

Primary bone lymphoma should always be considered as a differential diagnosis in patients exhibiting diffuse marrow changes with soft tissue component and relatively little cortical destruction. MR imaging in conjunction with PET/CT and biopsy is helpful in suggesting the diagnosis leading to early treatment.

Written informed patient consent has been obtained.