Symptoms are commonly attributed to other conditions and other diagnoses may have been made years before diagnosis, e.g. urinary symptoms in men attributed to common prostate conditions. Lesions may also be detected incidentally on radiological images, but can be easily misdiagnosed as malignancies.Reported cases do include some significant symptoms or findings however:

Individual organ manifestations
IgG4-RD can involve one or multiple sites in the body. With multiorgan involvement, the sites involved can be affected at the same time (synchronously) or at different unrelated periods (metachronously). Several different diseases that have been known for many years are now considered to be manifestations of IgG4-RD. These include: type 1 autoimmune pancreatitis, interstitial nephritis, Riedels thyroiditis, Mikuliczs disease, Küttners tumor, inflammatory pseudotumors (in various sites of the body), mediastinal fibrosis and some cases of retroperitoneal fibrosis. This is not a complete list, as IgG4-RD can involve any site in the body. Other affected sites, confirmed on histology to be manifestations of IgG4-RD, include:
heart; hard palate, esophagus, stomach, small intestine, rectum, adrenal gland, ovary, uterus, ureter, bladder, urachus, and synovium. Approximately 1/3 of cases exhibit increases in blood eosinophil counts, either eosinophilia or hypereosinophilia.Radiologic evidence suggestive of involvement of the superior vena cava and seminal vesicle has been reported in confirmed cases of IgG4-RD. Histology
Whatever area of the body is involved, the hallmark histopathological features of IgG4-RD are:
A dense lymphoplasmacytic (lymphocytes and plasma cells) infiltrate rich in IgG4-positive plasma cells. IgG4 immunostaining needs to be specifically requested and performed in order to detect IgG4-positive plasma cells.
Trials
Research is also underway to evaluate the effect and safety of plasmablast-directed therapy with a monoclonal antibody (XmAb5871) which inhibits B-cell function without depleting these immune cells. XmAb5871 targets CD19 with its variable domain and has an Fc domain that has increased affinity to FcγRIIb. Epidemiology
As recognition of IgG4-RD is relatively recent, there are limited studies on its epidemiology. It is therefore difficult to make an accurate estimation of prevalence. Furthermore, age of onset is almost impossible to estimate; age at diagnosis is frequently misused as the age of onset. A 2011 study estimated the incidence of IgG4-RD in Japan at 2.8–10.8/million population, with a median age of onset of 58 years. Nomenclature
Prior to 2011, IgG4-RD used to get mentioned in the medical literature under various different names.At the 2011 International Symposium on IgG4-Related Diseases, the consensus name of IgG4-related disease was endorsed for the condition. This name had already been agreed upon as a consensus name among Japanese investigators, notably choosing not to use the term systemic as that might lead to malignant tumours in other organs getting incorrectly diagnosed as being just another manifestation of the IgG4-related condition.However, some experts at the international symposium did express reservations about naming the disease after IgG4, as its role in pathogenesis is questionable and the use of serum IgG4 concentrations as a biomarker is unreliable.An expanded term, Immunoglobulin G4-related disease, has sometimes been used also. However, this term was never referenced in the 2012 recommendations for nomenclature, and its use would appear to be erroneous.