[Rheumatoid arthritis combined with pigmented villonodular synovitis: A case report and literature review]

We reported a case of rheumatoid arthritis (RA) combined with pigmented villonodular synovitis (PVNS) from Peking University People's Hospital. The clinical data were introduced and the related literature was reviewed. The clinical features, treatment and prognosis of the disease were summarized to improve clinicians' understanding of this rare disease and avoid misdiagnosis and delayed diagnosis. A 45-year-old female, with 15 years of RA history and unregular treatment, was admitted to the hospital with the complaint of aggravating pain and swelling in the right knee for 3 months. The puncture of the right knee was performed and there was a large amount of bloody synovial fluid that could not be explained by her RA history. Moreover, the magnetic resonance imaging (MRI) of the right knee revealed hemosiderin deposition with low-intensity signals on both T1-weighted and T2-weighted images which suggested PVNS to us. Then, the patient underwent knee arthroscopy and biopsy to assist in diagnosis. The arthroscopic appearance and pathology were consistent with PVNS and the hyperplastic synovium was removed during arthroscopy. After the operation, she did active functional exercises and took disease-modifying antirheumatic drugs to control RA. She recovered well and remained asymptomatic after half a year of follow-up. Also, there was no recurrence of the right knee. As we all know, RA is a systemic autoimmune disease characterized by chronic synovitis and joint damage. And PVNS is characterized by synovial proliferation and infiltrative process. Both of them are synovial involvement and the clinical manifestations are quite similar. PVNS has occasionally been reported in association with RA. So it is difficult to make a clear diagnosis of RA combined with PVNS. Literature was searched with RA+PVNS in the WanFang Medical Network Database and China National Knowledge Infrastructure and there were no related Chinese cases. Then we searched literature from PubMed with RA+PVNS. The cases were still rare and eventually 2 related articles were yielded including 2 similar patients. It is necessary to fully understand the disease development, complicated MRI appearance and various pathological morpho-logy. They can contribute to making a correct diagnosis which is effective to guide the proper treatment.