Autoimmune pancreatitis is a rare type of chronic pancreatitis with characteristic clinical, radiologic, and histopathologic findings. Diagnosis of autoimmune pancreatitis is often challenging due to its low incidence and nonspecific clinical and radiologic findings. Patients with autoimmune pancreatitis and pancreatic cancer share similar clinical presentations, including obstructive jaundice, abdominal pain and weight loss. Due to these overlapping features, autoimmune pancreatitis patients are often misdiagnosed with pancreatic cancer and undergo unnecessary surgery. International Consensus Diagnostic Criteria for autoimmune pancreatitis lists 5 cardinal features to establish the diagnosis of autoimmune pancreatitis. These features include imaging, serology, other organ involvement, histopathology of the pancreas, and response to steroid therapy. Endoscopic ultrasound-guided fine needle aspiration is a routine diagnostic tool for pancreatic lesions. It is usually utilized to exclude a malignant process in autoimmune pancreatitis patients, since its role to establish a definitive diagnosis of autoimmune pancreatitis is often limited. Endoscopic ultrasound-guided-tru-cut biopsy and endoscopic ultrasound-guided fine needle using a large gauge needle (19 to 22 gauges) have been the preferred methods to obtain tissue samples for histologic evaluation. Lymphoplasmacytic infiltrates, fibrotic stroma, mildly atypical epithelial cells, periphlebitis, and obliterative periphlebitis are the common histologic findings of type 1 autoimmune pancreatitis. Meanwhile, granulocytic pancreatic ductal epithelial damage and ductal obliteration are the histologic characteristics of type 2 autoimmune pancreatitis. Immunohistochemical and molecular studies may be helpful to support the diagnosis of AIP in biopsy materials.
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