Primary Bone Lymphoma of the Patella

Background: Primary bone lymphoma (PBL) is a rare bone malignancy that accounts for 7% of all bone tumors. It most commonly involves the long bones, with the distal femur and the proximal tibia being the most common locations. The majority of patients present during adulthood with pain in the absence of trauma. Methods: A case report of a 15 year-old male, with a 6-month history of insidious onset right peripatellar pain. After arriving to our clinic he presented with a 30-pound weight loss over the last year, right inguinal adenopathy and tenderness in the patellar area. Imaging showed an osteolytic lesion of the right patella and an imaging-guided biopsy was performed. Awaiting results, he presented with a non-displaced fracture of the patella while he was walking down the stairs. Treatment with a knee brace and COPAD chemotherapy regime was initiated after a diagnosis of bone lymphoma was established. Results: Our patient received 6-months of chemotherapy and knee immobilization for his pathologic fracture. There was good response to the chemotherapy and no complications arised after the fracture. Our patient is now 2-years after diagnosis, without signs of recurring disease and back to his normal daily activities. Conclusion: There are few reports of PBL arising from the patella in the literature. Most of these reports do not distinguish by age, and the few that do, show patients between 38-77 years of age. To our knowledge, this is the first report of a patellar primary bone lymphoma in the pediatric population. Anterior knee pain is extremely common and its differential diagnosis is very wide. Anterior knee pain is more commonly related to tendinitis, patellar malalignment syndrome and chondromalacia. Clinicians should keep in mind the possibility of a malignant process as a possible underlying cause when there is lack of response to conventional treatment.