Role of endoscopic ultrasound in diagnosis and management of autoimmune pancreatitis

Autoimmune pancreatitis (AIP) is a rare inflammatory disorder of the pancreas, often mistaken for pancreatic cancer. Despite definitive diagnostic criteria such as histology, imaging, serology, other organ involvement and response to therapy (HISORt), International Consensus Diagnostic Criteria (ICDC) and Japan Pancreas Society (JPS) criteria being available for AIP, making a diagnosis of AIP remain a rarity in the evaluation of a pancreatic mass or distal bile duct obstruction. A significant proportion of patients are diagnosed only after surgical resection. Endoscopic ultrasound (EUS) is the main modality for establishing diagnosis of AIP. Considering the rarity of the disease, there are no classical findings on EUS associated with AIP. Histopathology remains the crux for diagnosing AIP with need for EUS-guided sampling. Both focal and diffuse forms of AIP are described with different EUS findings in both. The focal form mimics pancreatic cancer closely. The disease is also known to have extra-pancreatic involvement with cholangiopathy also seen often in association. Diffuse involvement of the pancreas is unusual and may be rarely seen with diffuse pancreatic infiltrative diseases. The primary consideration remains differentiating AIP from carcinoma of pancreas, where EUS plays a significant role. Adjunct techniques such as EUS-guided elastography and contrast harmonic EUS can add value in diagnosing AIP. Advances in tissue sampling, including availability of better needles for core biopsy, have aided in improving the diagnostic yield of AIP. In this narrative review, we aim to highlight the increasing role of EUS for establishing diagnosis of AIP while elaborating its role in evaluation, sampling and therapeutic monitoring.