[citation needed] Reported cases do include some significant symptoms or findings however: IgG4-RD can involve one or multiple sites in the body.

Other affected sites, confirmed on histology to be manifestations of IgG4-RD, include: heart;[14] hard palate,[51] esophagus,[26][27] stomach,[52] small intestine,[53] rectum,[54] adrenal gland,[55] ovary,[56] uterus,[24] ureter,[57] bladder,[58] urachus,[59] and synovium.

[citation needed] Radiologic evidence suggestive of involvement of the superior vena cava[14] and seminal vesicle[61] has been reported in confirmed cases of IgG4-RD.

Whatever area of the body is involved, the hallmark histopathological features of IgG4-RD are:[3][32][33] Other histopathological features associated with IgG4-RD are: In an article from 1977, histological research into 349 cases of Küttner's tumor (now known as 'IgG4-related sialadenitis') identified four distinct stages of the fibroinflammatory process:[62] This may reflect the inflammatory process and development of fibrosis that occurs in other organs involved in IgG4-RD.

Urgent treatment is advised with certain organ manifestations, such as aortitis, retroperitoneal fibrosis, proximal biliary strictures, tubulointerstitial nephritis, pachymeningitis, pancreatic enlargement and pericarditis.

In untreated patients with active disease, the recommended first-line agent for induction of remission is glucocorticoids unless contraindications exist.

However, where advanced fibrotic lesions have resulted in irreversible damage, the response to glucocorticoids and other current treatment options may be poor or even absent.

Although not validated yet in clinical trials, the common induction regime is prednisolone 30–40 mg per day for 2–4 weeks, then gradually tapered over 3 to 6 months.

Following a successful induction of remission, maintenance therapy might be given in some cases, for example when there is a high risk of relapse or in patients with organ-threatening manifestations.

Introducing a steroid-sparing agent might also need to be considered for relapses; however, none has been tested in prospective, controlled studies, and evidence for their efficacy beyond that offered by concomitant glucocorticoid therapy is scarce.

Research is also underway to evaluate the effect and safety of plasmablast-directed therapy with a monoclonal antibody (XmAb5871, obexelimab) which inhibits B-cell function without depleting these immune cells.

[66] 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.