IgG4‐related disease: a new kid on the block or an old aquaintance?

IgG4-related systemic disease is a recently recognized systemic condition characterized by unique pathological features that can affect a variety of organs. It includes a growing number of medical conditions which have the following features in common: diffuse organ swelling or focal mass formation, sclerosing storiforme (whirl-shaped) fibrosis with a lymphoplasmacytic infiltrate rich in IgG4-bearing plasma cells, as well as elevated levels of serum IgG4. It invariably responds to steroid treatment and is mostly diagnosed in elderly men. Well-known syndromes like Mikulicz's disease of the salivary or lacrimal gland, Küttner's tumour of the submandibular gland, Riedel's thyroiditis, or retroperitoneal fibrosis, as well as novel entities such as autoimmune pancreatitis type 1, are now regarded to be manifestations of this systemic disease. This article provides an overview of the epidemiology, concepts of pathogenesis, clinical presentation, proposed diagnostic approaches, treatment options, and differential diagnosis of IgG4-related disease.