Periarticular Other Iatrogenic Immunodeficiency-associated Lymphoproliferative Disorder Mimicking Knee Synovitis in a Patient with Rheumatoid Arthritis.

Other iatrogenic immunodeficiency-associated lymphoproliferative disorders (OIIA-LPDs) develop in patients with rheumatoid arthritis (RA) during treatment with disease-modifying antirheumatic drugs (DMARDs). Periarticular OIIA-LPDs are rare and poorly understood. An 81-year-old woman with RA presented with knee swelling, a fever, and weight loss. Imaging studies revealed bone erosion and a 18F-fluorodeoxyglucose uptake around the knees. A histopathological analysis was consistent with diffuse large B-cell lymphoma, confirming the diagnosis of OIIA-LPD. Discontinuation of DMARDs resolved the knee swelling and prevented further bone erosion. This report highlights the importance of considering OIIA-LPDs in patients with RA, atypical joint swelling, and systemic symptoms.