IgG4-related disease (IgG4-RD), formerly known as IgG4-related systemic disease, is a chronic inflammatory condition characterized by tissue infiltration with lymphocytes and IgG4-secreting plasma cells, various degrees of fibrosis (scarring) and a usually prompt response to oral steroids. In approximately 51–70% of people with this disease, serum IgG4 concentrations are elevated during an acute phase.It is a relapsing-remitting disease associated with a tendency to mass forming, tissue-destructive lesions in multiple sites, with a characteristic histopathological appearance in whichever site is involved. Inflammation and the deposition of connective tissue in affected anatomical sites can lead to organ dysfunction, organ failure, or even death if not treated.Early detection is important to avoid organ damage and potentially serious complications. Treatment is recommended in all symptomatic cases of IgG4-RD and also in asymptomatic IgG4-RD involving certain anatomical sites. Signs and symptoms
IgG4-related disease has been described as an indolent condition. Although possibly based on opinion rather than on objective assessments, symptoms, if any, are commonly described as mild in the medical literature. This can be in spite of considerable underlying organ destruction. People are often described as being generally well at the time of diagnosis, although some may give a history of weight loss. Pain is generally not a feature of inflammation. However, it may occur as a secondary effect, for example, due to either obstruction or compression. Often diagnosis is made due to the presence of painless swellings or mass lesions, or due to complications of masses, e.g. jaundice due to involvement of the pancreas, biliary tree or liver.
Fibrosis, arranged at least focally in a "storiform" pattern. "Storiform" is commonly referred to as meaning having a cartwheel pattern, but its literal meaning is the appearance of a woven mat [Latin: storea] (of rush or straw). Obliterative phlebitis. The venous channels are obliterated by a dense lymphoplasmacytic infiltrate, within both the venous walls and the lumen.Other histopathological features associated with IgG4-RD are:

Phlebitis without obliteration of the lumen. Tissue has increased numbers of eosinophils. Submandibular gland research
In an article from 1977, histological research into 349 cases of Küttners tumor (now known as IgG4-related sialadenitis) identified four distinct stages of the fibroinflammatory process:
Stage 1: Focal periductal (around the salivary ducts) infiltration of lymphocytes
Stage 2: Diffuse infiltration of lymphocytes and severe periductal fibrosis (scarring around the salivary ducts)
Stage 3: Prominent infiltration of lymphocytes, atrophy of parenchyma (i.e. loss of functional areas due to shrinkage), and periductal sclerosis (scarring resulting in hardening around the salivary ducts)
Stage 4: Marked loss of and sclerosis (hardening) of the parenchyma (functional area) - similar to the process involved in cirrhosis where there is shrinkage and loss of functional areas of the liverThis may reflect the inflammatory process and development of fibrosis that occurs in other organs involved in IgG4-RD. Diagnosis
Diagnosis requires tissue biopsy of an affected organ with characteristic histological findings. Serum immunoglobulin G4 is often elevated but this is not always the case. Treatment
The goal of treatment is the induction and maintenance of remission so as to prevent progression of fibrosis and organ destruction in affected organ(s).