Autoimmune pancreatitis (AIP) is a rare disease which is characteristically responsive to steroid treatment. Its clinical presentation mimics that of pancreatic cancer which is far more common than AIP. The price of misdiagnosis is heavy as AIP mistaken for pancreatic cancer leads to major pancreatic surgery. Similarly, pancreatic cancer misdiagnosed as AIP leads to delay in diagnosis and possible progression of cancer while receiving steroid therapy. Recently, international consensus diagnostic criteria have been formulated for the diagnosis of AIP and to distinguish it from pancreatic cancer. These criteria utilize a combination of histology, pancreatic imaging features, evidence of extrapancreatic manifestations, IgG4 serology, and response to steroid treatment. Histological confirmation of AIP is difficult preoperatively; however, noninvasive diagnosis of AIP can be made in about 50 % of patients based on radiological and serological features. In a select group of patients with specific features, a diagnostic steroid trial is appropriate. About 20 % of patients do not have any evidence of extrapancreatic organ involvement or IgG4 serum elevation; in these patients, histological confirmation is required to definitively diagnose AIP.
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