The patient was a 72-year-old woman with a long-standing history of localized synovial disease. She first presented with right elbow swelling and pain in 2002 and underwent surgery; postoperative histopathology confirmed pigmented villonodular synovitis (PVNS). Five years later, in 2007, she developed left elbow symptoms and had a second synovectomy with pathology again consistent with PVNS. Symptoms recurred in large joints beginning in 2021, progressing from isolated monoarticular disease to recurrent bilateral knee involvement and eventually symmetric polyarthritis affecting wrists and other small joints by April 2024.
Short sentences punctuate an extended timeline. PVNS was established early. Later, the pattern of joint involvement and systemic inflammation shifted clinicians' differential diagnosis toward inflammatory arthritis.
During an acute presentation in June 2023 laboratory evaluation demonstrated marked systemic inflammation: C-reactive protein (CRP) 175.3 mg/L and erythrocyte sedimentation rate (ESR) 116 mm/h. The patient was anemic (hemoglobin 83 g/L) and thrombocytotic (platelet count 537×10^9/L). Serologic testing for common rheumatoid markers was negative: rheumatoid factor, anti-cyclic citrullinated peptide (anti-CCP) antibody, anti-keratin antibody, and anti-perinuclear factor were all reported as negative. The authors therefore categorized the case as seronegative rheumatoid arthritis (SNRA) in the context of prior PVNS.
Right knee MRI performed before joint replacement showed severe degenerative change, suprapatellar bursitis with a large effusion, and ligamentous injuries. The imaging did not demonstrate the nodular synovial masses that characterized her earlier elbows, and clinicians could not rely on imaging alone to separate recurrent PVNS from emerging systemic arthritis.
Right knee replacement was undertaken in the setting of advanced joint disease and prior PVNS history. Intraoperatively the surgeon did not observe the nodular or mass-like synovial proliferation typical of PVNS. The postoperative synovial pathology instead revealed massive chronic inflammatory cell infiltration, small vessel proliferation, and areas of fibrinoid necrosis. The study team reported these features as consistent with rheumatoid arthritis rather than PVNS.
That histopathology shifted the working diagnosis. Where imaging and clinical history produced diagnostic ambiguity, tissue examination provided decisive evidence favoring an inflammatory arthropathy over recurrent localized synovial neoplasm.
Following the revised diagnosis the patient began disease-modifying therapy with intravenous tocilizumab 400 mg monthly combined with methotrexate 10 mg weekly. The paper reported biochemical remission of inflammation after three months: CRP fell to 0.73 mg/L and ESR to 6 mm/h. Clinical symptom details and longer-term functional outcomes beyond the three-month laboratory response were not reported in the abstract.
The authors emphasized that appropriate immunotherapy produced a rapid normalization of systemic inflammatory markers in this patient, suggesting treatment responsiveness despite seronegativity. Specifics such as dose adjustments, adverse events, or objective functional scores were not described in the source abstract.
The authors conducted a literature search across Wanfang, CNKI, and PubMed using terms pairing “rheumatoid arthritis” with “pigmented villonodular synovitis.” They identified four previously published cases and combined those with the present report to summarize features of five total patients. Demographics and patterns were heterogeneous: four females and one male; the median age at PVNS onset was 45 years (reported interquartile statistics in the source). The knee was most frequently involved (4 of 5 cases), followed by the elbow.
Temporal relationships varied between disorders. PVNS preceded rheumatoid arthritis in two patients (intervals of 3 and 12 years), RA preceded PVNS in two others (3 and 15 years), and one case had simultaneous onset. Serostatus differed across reports: four of the five patients were seropositive for RF/anti-CCP, making the index case the sole seronegative patient in the aggregated series. All five underwent synovial resection; two experienced postoperative recurrence.
Clinical overlap between PVNS and RA produced diagnostic uncertainty in this case and in the reviewed reports. The authors argued that clinicians should suspect RA when a patient with prior PVNS develops symmetric polyarthritis, and conversely consider PVNS when a patient with RA has persistent monoarticular symptoms resistant to disease-modifying therapy. They recommended integrating synovial fluid analysis, MRI characteristics, and—most critically—histopathological examination to differentiate the entities.
Limitations are present in the source. The abstract does not provide long-term clinical follow-up beyond three months of biochemical response. Detailed functional outcomes, adverse event reporting for immunotherapy, and molecular or immunohistochemical studies linking PVNS and RA in this patient were not provided. The literature synthesis is limited to case reports; no controlled data were available to quantify recurrence risk or to guide therapy choice between synovectomy versus systemic immunomodulation.
These gaps frame unanswered questions: what drives the temporal association between PVNS and RA in some patients, which biomarkers might predict coexistence, and what are the optimal surveillance and treatment strategies for patients with both diagnoses? The source calls for careful tissue diagnosis and individualized management but does not supply definitive protocols or long-term outcome data.