The occurrence of remitting seronegative symmetrical synovitis with pitting edema (RS3PE) after arthroplasty mimicking a periprosthetic joint infection: A case report and literature review.

Rationale: As the elderly population grows, the number of joint arthroplasty surgeries is also increasing. Periprosthetic joint infection (PJI) is a postoperative complication that occurs in 1%-2% of the arthroplasties. Once it occurs, PJI is refractory to treatment. Similar symptoms of PJI, including joint synovitis and elevated body temperature, sometimes arise because of crystal arthritis, rheumatoid arthritis, or other inflammatory diseases. Precise diagnosis is essential for determining the optimal treatment strategy.

Patient concerns: An 81-year-old female patient with a history of bilateral knee arthroplasty presented with a high fever of 38 °C and was unable to walk due to swelling and pain in the bilateral lower extremities. Infectious conditions, such as cellulitis or PJI, were suspected. Imaging findings revealed bilateral knee joint synovitis with pitting edema around the lower extremities, and cultures of bilateral joint fluids were negative. No crystals were observed in the joint fluid. Laboratory data revealed highly elevated levels of inflammatory marker; however, antinuclear antibodies, including rheumatoid factor and cyclic citrullinated peptide, were not detected.

Diagnoses: Based on bilateral synovitis with pitting edema in the lower extremities, in addition to negative culture findings and normal antinuclear antibodies, the diagnosis of remitting seronegative symmetrical synovitis with pitting edema (RS3PE) was made.

Interventions: Steroid therapy was performed. The dose was gradually reduced, with the improvement of the symptoms.

Outcomes: The inflammatory reaction promptly decreased and then normalized. With improved inflammation, the symptoms of pitting edema, pain in the bilateral lower extremities, and fluid effusion of the knee joints were reduced. She was able to walk without a cane, and her activities of daily living fully recovered.

Lessons: High fever and synovitis after joint arthroplasty do not necessarily indicate an infectious condition. Clinicians should be familiar with the occurrence of RS3PE, regardless of whether arthroplasty is performed.