type 1 AIP:
pancreas involved as part of an IgG4 systemic disease + meets HISORt criteria
characteristic pancreatic histopathologic findings: lymphoplasmacytic infiltrate, storiform fibrosis, and abundant IgG4 cells.
AIP type 2:
histologically confirmed idiopathic duct centric pancreatitis w/ granulocytic infiltration of duct wall (termed GEL), but w/o IgG4 positive cells and systemic involvement.
AIP initially described as a primary pancreatic disorder, now a w/ other disorders of presumed autoimmune etiology, and has been termed IgG4 systemic disease
clinical features: IgG4-associated cholangitis, rheumatoid arthritis, Sjögren’s syndrome, ulcerative colitis, mediastinal fibrosis and adenopathy, autoimmune thyroiditis, tubulointerstitial nephritis, retroperitoneal fibrosis, chronic periaortitis, chronic sclerosing sialadenitis, and Mikulicz’s disease. Mild symptoms, u. abdominal pain, and recurrent acute pancreatitis are unusual.
not a common cause of idiopathic recurrent pancreatitis. Weight loss and new onset of diabetes may occur.
obstructive pattern on liver tests common (i.e., disproportionately elevated serum alkaline phosphatase and minimally elevated serum aminotransferases). Elevated serum levels of IgG4 provide a marker for the disease
CT: abnormalities in majority of pxs: diffuse enlargement, focal enlargement, and a distinct enlargement at head of pancreas.
ERCP or MRCP: strictures in bile duct in >1/3 of (common bile duct, intrahepatic bile duct, or proximal bile duct strictures) w/ accompanying narrowing of pancreatic portion of bile duct: AI IgG4 cholangitis: charac histologic findings: extensive lymphoplasmacytic infiltrates w/ dense fibrosis around pancreatic ducts, as well as a lymphoplasmacytic infiltration, resulting in an obliterative phlebitis.
Mayo Clinic HISORt criteria: AIP can be dx by presence of at least two of: (1) histology; (2) imaging; (3) serology (elevated serum IgG4); (4) other organ involvement; and (5) response to glucocorticoid therapy, w/ improvement in pancreatic and extrapancreatic manifestations.
Glucocorticoids: alleviate symptoms, decr size of pancreas, reverse histopathologic features; decr serum γ-globulin and IgG4, improvements in liver tests
poor response to glucocorticoids over 2- to 4-week--> raise suspicion of pancreatic cancer or other forms of chronic pancreatitis.
Types 1 and 2 AIP: highly responsive to initial glucocorticoid treatment. Relapse common in type 1, esp w/ biliary tract strictures. Most relapses occur after glucocorticoids discontinued. pxs w/ refractory symptoms and strictures generally require immunomodulator therapy. Appearance of interval cancers following a diagnosis of AIP is uncommon.