Remitting seronegative symmetrical synovitis with pitting oedema syndrome with pleural, pericardial and peritoneal serositis

We report an exceptional case of remitting seronegative symmetrical synovitis with pitting oedema (RS3PE) in a woman in her 70s presenting with extensive serositis, including pericardial, pleural and peritoneal effusions. Serositis is an unusual finding in RS3PE, and while a few cases with pleural or pericardial effusion have been described, the presence of ascites has not been previously reported in idiopathic RS3PE without associated malignancy. The patient exhibited classical features of RS3PE along with systemic inflammation and responded well to corticosteroids and methotrexate. This case expands the clinical spectrum of RS3PE and highlights the need to consider this diagnosis in elderly patients with unexplained polyserositis and inflammatory arthritis.