Primary Bone Lymphoma of the Tibia Mimicking Chronic Osteomyelitis: A Case Report.

Introduction: Primary bone lymphoma (PBL) is a rare malignancy that often presents with non-specific symptoms and radiological features, making it easily mistaken for infectious or inflammatory conditions. Among its various presentations, tibial involvement mimicking chronic osteomyelitis is particularly uncommon. Case Report: We report the case of a woman in her 50s with a 6-year history of progressive pain and swelling of the left upper leg. She had previously received multiple empirical antibiotic courses for presumed osteomyelitis over 6 years without sustained benefit. Persistent symptoms and inconclusive radiology prompted further evaluation. Core and open biopsies confirmed diffuse large B-cell lymphoma of the proximal tibia. Immunohistochemistry showed positivity for CD45 and CD20, with a high Ki-67 index (60%), establishing the diagnosis. The patient underwent four cycles of R-CHOP chemotherapy. Given the associated cortical destruction and pathological fracture risk, surgical fixation was deferred. She was managed with a hinged knee brace and structured rehabilitation. At 4 months follow-up, she remained asymptomatic, mobile with a cane, and radiologically stable. Conclusion: This case underscores the diagnostic challenge of PBL when it masquerades as chronic osteomyelitis. Early tissue biopsy and immunohistochemistry are critical to avoid prolonged misdiagnosis and inappropriate therapy. Clinicians should maintain a high index of suspicion for malignancy in non-resolving bone lesions.