Autoimmune Pancreatitis - A Riddle Wrapped in an Enigma

Autoimmune pancreatitis (AIP) was recognized as a clinical entity, at least in the West little more than 10 years ago. Since then, studies globally, and international collaboration, have led to important advances in our understanding of its clinical features, disease course, and management, although the aetiopathogenesis of this curious disease remains to be fully elucidated. Types 1 and 2 AIP have been described, of which type 1 is the commonest form, and best defined. International consensus now recognizes it as one of the many clinical manifestations of IgG4-related disease, and is now termed IgG4-related pancreatitis (IgG4-RP). The disease is not confined to a particular race, gender, or age, but often presents after the fifth decade in men. A common presentation is with jaundice due to low bile duct obstruction related to diffuse pancreatic enlargement (historically often leading to a misdiagnosis of cancer). Acute pancreatitis is unusual. Other organ involvement is a particular feature, including biliary disease, retroperitoneal fibrosis, generalized lymphadenopathy, renal, and lung involvement. No single test makes the diagnosis, and diagnostic criteria for type 1 AIP/IgG4-RP, which incorporate clinical, laboratory, radiological, pathological, and therapeutic parameters should be applied. A particular attempt should be made to make a histological diagnosis, which is characterized by an IgG4-positive lymphoplasmacytic infiltrate. Management is not based on randomized studies, but corticosteroids are the mainstay of treatment, providing rapid clinical and radiological benefit. However, clinical relapse is common (particularly in type 1 AIP, and in those with associated other organ involvement). Additional immunosuppression may be required, including azathioprine, and rituximab may play an emerging role. The disease course is variable, but loss of organ function (especially pancreatic exocrine failure and pancreatic atrophy) may occur.