Mechanisms and assessment of IgG4-related disease: lessons for the rheumatologist.

Recognition of IgG4-related disease as an independent chronic inflammatory disorder is a relatively new concept; previously, the condition was thought to represent a subtype of Sjögren's syndrome. IgG4-related disease is characterized by elevated serum levels of IgG4 and inflammation of various organs, with abundant infiltration of IgG4-bearing plasma cells, storiform fibrosis and obliterative phlebitis representing the major histopathological features of the swollen organs. The aetiology and pathogenesis of this disorder remain unclear, but inflammation and subsequent fibrosis occur due to excess production of type 2 T-helper-cell and regulatory T-cell cytokines. The disease can comprise various organ manifestations, such as dacryoadenitis and sialadenitis (also called Mikulicz disease), type 1 autoimmune pancreatitis, kidney dysfunction and lung disease. Early intervention using glucocorticoids can improve IgG4-related organ dysfunction; however, patients often relapse when doses of these agents are tapered. The disease has also been associated with an increased incidence of certain malignancies. Increased awareness of IgG4-related disease might lead to consultation with rheumatologists owing to its clinical, and potentially pathogenetic, similarities with certain rheumatic disorders. With this in mind, we describe the pathogenic mechanisms of IgG4-related disease, and outline considerations for diagnosis and treatment of the condition.