IgG4-related disease is a novel
lymphoproliferative disorder that shows hyper-IgG4-γ-globulinemia and IgG4-producing plasma cell expansion in affected organs with fibrotic or sclerotic changes. Patients show systemic inflammatory conditions and various symptoms depending on the affected organ. Since the first report of patients with elevated serum
IgG4 in sclerosing
pancreatitis in 2001, various systemic disorders described by many names have been reported. Despite similarities in the organs involved in IgG4-related
Mikulicz's disease and Sjögren's syndrome, there are marked clinical and pathological differences between these conditions. Most patients diagnosed with
autoimmune pancreatitis in Japan have
IgG4-related pancreatitis [
Type 1 autoimmune pancreatitis (AIP), lymphoplasmacytic sclerosing
pancreatitis (LPSP)], a disease distinct from some of the western type [
Type 2 AIP, idiopathic duct-centric
chronic pancreatitis (IDCP),
autoimmune pancreatitis with granulocytic epithelial lesions (GEL)]. Diagnosis of
IgG4-related disease is characterized by both elevated serum
IgG4 (>135 mg/dL) and histopathological features including lymphocyte and
IgG4(+) plasma cell infiltration (
IgG4(+) plasma cells/
IgG(+) plasma cells>40%). Differential diagnosis from other distinct disorders, such as
sarcoidosis,
Castleman's disease,
Wegener's granulomatosis,
lymphoma,
cancer, and other existing conditions associated with high serum
IgG4 level or abundant IgG4-bearing plasma cells in tissues is necessary. We have begun a clinical prospective study to establish a treatment strategy (Phase II prospective treatment study for
IgG4-multiorgan lymphoproliferative syndrome: UMIN R000002311).