Case Report: Rheumatoid Arthritis Combined With Pigmented Villonodular Synovitis: A Report of Two Cases.

This report presents two rare cases of rheumatoid arthritis (RA) complicated by pigmented villonodular synovitis (PVNS), highlighting the diagnostic and therapeutic challenges posed by their coexistence. RA is a chronic autoimmune disease characterized by joint inflammation and destruction, while PVNS is a rare proliferative synovial disorder that often presents with monoarticular joint involvement. The overlap in clinical and radiological features between RA and PVNS complicates diagnosis, necessitating advanced imaging techniques and histopathological evaluation for accurate differentiation. In the first case, an 85-year-old woman with a long-standing history of RA developed PVNS in the left knee, confirmed by MRI findings of hemosiderin deposition and nodular synovial hypertrophy. In the second case, a 72-year-old woman with seronegative RA and a prior history of PVNS in the elbows presented with PVNS in the left knee, confirmed by both imaging and pathology. Both patients underwent successful treatment involving a combination of systemic therapies, including disease-modifying antirheumatic drugs (DMARDs) and biologics, as well as localized interventions, such as synovectomy and corticosteroid injections. These cases underscore the importance of integrating imaging and histopathology in managing RA patients with persistent joint symptoms, as well as the necessity for a tailored therapeutic approach to address both systemic inflammation and localized pathology. A comprehensive literature review is provided to contextualize these findings, with a focus on the role of MRI and emerging therapies, such as colony-stimulating factor-1 receptor (CSF-1R) inhibitors, in the management of PVNS.