Definition:

Immunoglobulin G4-related disease is a distinct clinical entity characterised by hyper-IgG4 gammaglobulinemia and IgG4 positive plasma cell infiltration in the tissue. Other characteristic features of this syndrome include mass-forming lesion with fibrosis and prompt and good response to corticosteroids. This disease includes Mikulicz's disease (MD), autoimmune pancreatitis, sclerosing cholangitis, Kuttner's tumour, inflammatory pseudotumor of the lung, liver, and breast, retroperitoneal and mediastinal fibrosis, interstitial nephritis, autoimmune hypophysitis, and many other inflammatory conditions in multiple organs. Glucocorticoids are the mainstay of treatment; recently, rituximab, a select B-cell depleting agent, has been shown to provide an excellent clinical response in select patients.