Recurrent Pleural Effusion: Not Tuberculosis and Not a Malignancy Either

A 47-year-old male with signs of metabolic syndrome, tobacco exposure of 3 pack years and a medical history of pancreatitis and myocardial infarction presented with unilateral pleural fluid which evolved to recurrent sometimes bilateral pleural fluid. Despite rigorous diagnostic efforts a clear diagnosis could not be established. Eventually on an abdominal ultrasound pancreatic abnormality was detected leading to a suspected diagnosis of autoimmune pancreatitis and giving way to a diagnosis of pleurisy due to Immunoglobulin G4 Related Disease (IgG4 RD) based on the 2019 ACR/EULAR classification criteria for IgG4 RD. Treatment with corticosteroids followed by rituximab resulted in sustained resolution of the pleural fluid and patient improvement.