Enchondroma was the differential considered and the patient attended tertiary care services for possible biopsy to ascertain the histological diagnosis. 

Guided bone biopsy revealed an aggressive lesion for a gelatinous tissue obtained. Histology showed NHL, diffuse large B cell (DLBCL) type which was infiltrating the bone. Immunohistochemistry stained for CD45 and CD20 (strong). It was negative for cytokeratin cam 5.2 and AE 1/3, CD138 and CD3 (reactive T cells). 

A final diagnosis was made of multifocal primary bone DLBCL involving the left proximal humerus and right tibia, with no other evidence of systemic involvement. The patient received treatment with standard protocol and achieved good response which was confirmed on the post treatment scans.

Discussion

Primary bone lymphoma (PBL) is a rare entity and comprises < 5% of extranodal lymphomas and < 1% of NHL. Bone pain, mass or both limited to a single focus or disseminated disease, are common presenting features. Males are more commonly inflicted with the median age at diagnoses between 40 and 60 years.¹²

What are the diagnostic criteria for primary bone lymphoma?

Differential diagnosis for PBL is based on radiographic examination and age of the patient. Metastatic carcinoma, osteosarcoma, Ewing’s sarcoma, osteomyelitis, Paget’s disease and giant cell tumour are among the list that should be considered in the differentials.¹²

Diagnosis is confirmed on clinical features, radiology findings and histology, with histology being the most definitive criteria.¹³ DLBCL is a common histology accounting for 80% of the cases. Axial skeleton has a predilection to be affected, compared to appendicular skeleton, with femur affected in one-third of case.¹³

Question 2: What are the treatment options?

Patients receive chemotherapy and radiotherapy as deemed appropriate. Randomised clinical trials for this disease are lacking. Chemotherapy alone results in favourable outcomes. Radiotherapy provides good local control but can result in treatment failure if used alone. Combination treatment with an addition of a monoclonal antibody has shown good clinical outcomes with improved survival rates.¹⁴

Question 3: What is the prognosis?

International Prognostic Index (IPI) score risk stratifies patients with DLBCL in four prognostic groups based on the following, with 1 point being assigned to each: 

• Age of ≥ 60 years
• Increased LDH levels
• Stage III/IV disease
• ECOG performance score of 2 or more 
• More than one extranodal site. 

Other risk stratification models are R-IPI, which is designed for use in patients receiving rituximab therapy, and NCCN-IPI, from the National Comprehensive Cancer Network. The risk stratification models are helpful in identifying high risk patients with DLBCL who might benefit from novel treatment modalities.¹⁵

Assessment of response to treatment is challenging since the residual bone changes and skeletal abnormalities makes it difficult to read the x-rays and MRIs. However, functional scans using PET-CT techniques can be useful. No radiopharmaceutical uptake noticed in the concerned radiological changes is satisfactory and indicative of good response to treatment.¹⁴