Symmetrical polyarthritis in IgG4-related sialadenitis: a diagnostic challenge with seronegative rheumatoid arthritis.

Background: IgG4-related disease (IgG4-RD) is a systemic fibro-inflammatory condition characterized by elevated IgG4 serum levels and tissue infiltration by IgG4-positive plasma cells. While often presenting with organ-specific involvement, such as sialadenitis or pancreatitis, its rheumatologic manifestations are rare and poorly understood. IgG4-RD often overlaps with autoimmune diseases such as rheumatoid arthritis (RA), posing a diagnostic challenge, particularly in seronegative presentations.