IgG4-Related Disease in a Rheumatoid Arthritis Patient- A Coincidence or Possible Association? Case Report

Abstract Immunoglobulin G4-related disease (IgG4-RD) is a newly emerging disease entity. IgG4-RD is a systemic disease characterized by swelling or masses in the involved organs, elevated serum immunoglobulin G4 (IgG4), and marked IgG4-positive plasma cells infiltration and fibrosis. The serum concentration of IgG4 increases not only in IgG4-RD but in a broad spectrum of rheumatologic and non-rheumatologic diseases. Elevated serum levels of IgG4 were demonstrated in some patients with rheumatoid arthritis (RA). Interestingly, it was suggested that RA patients who have elevated serum IgG4 levels are more prone to have higher disease activity, higher levels of autoantibodies, and poor response to methotrexate and leflunomide therapy. However, the association between RA and IgG4-RD remains elusive. Herein, we describe a case of a 64-year-old man with a known history of RA and RA-associated interstitial lung disease (RA-ILD) presented with unintentional weight loss, and a speculated lung nodule mimicking lung malignancy. As a result, he underwent a computer tomography (CT) guided biopsy of the lung nodule. Histological analysis revealed fibrous tissue with dense lymphoplasmacytic infiltrates, immunostaining indicated the presence of IgG4-positive plasma cells, serum IgG4 levels were elevated, and a definitive diagnosis of IgG4‐related disease was confirmed. He was started on Prednisone initially and then on Rituximab as a steroid-sparing agent.