IgG4 Autoimmune Pancreatitis: A G-Force Worth Fighting

Abstract

Introduction: Autoimmune Pancreatitis (AIP) is a rare but increasingly more recognized cause of chronic pancreatitis. AIP can be divided into Type 1 and Type 2, which are characterized by high amounts of IgG4 Plasma Cells and Granulocytic Epithelial Lesions, respectively. Until recently, most AIP was diagnosed in patients who underwent Pancreaticoduodenectomy due to concern for pancreatic cancer. With the advent of Endoscopic Ultrasound (EUS) and Fine Needle Biopsy (FNB), a less invasive realm for diagnosis and management is now utilized. Here we present a case of a patient with acute pancreatitis and a mysterious pancreatic mass.1304_A.tif Figure 1: CT scan image of tail of pancreas lesion1304_B.tif Figure 2: EUS image of tail of pancreas lesion1304_C.tif Figure 3: Representative H&E sections highlight a dense inflammatory infiltrate composed of lymphocytes, plasma cells and other mixed components, as well as fibrosis within the pancreatic parenchyma; C) IgG+ plasma cells, representative immunohistochemistry section; D) IgG4+ plasma cells, representative immunohistochemistry section.Case report: A 49 year old female presented with abdominal pain and a lipase of 1227. Though the patient had symptoms consistent with acute pancreatitis, she did not have any major risk factors nor familial history. CT Imaging revealed a 4 cm tail of pancreas solid mass. To rule out malignancy, an EUS was performed which showed 3.1 x 3.2 cm hypoechoic and heterogenous mass with poorly formed borders. FNB was successfully done with histopathology revealing storiform fibrosis without granulation, up to 25 IgG4 plasma cells in a high power field, and an IgG4/IgG ratio greater than 40%. The diagnosis of Type 1 AIP was made with a high serum IgG4 level of 109. Ultimately, a corticosteroid taper was initiated which brought resolution of the patient's symptomology. Discussion: Criteria for diagnosis of AIP include 5 distinct entities recognized by the mnemonic HISORt (histology, imaging, serology, organ involvement, and response to therapy). Imaging findings typically show a sausage shape of the pancreas, multifocal strictures, and a positive duct penetrating sign. Tissue histology for Type 1 AIP reveals sheets of plasma cells, storiform fibrosis, and positive IgG4 immunostaining of plasma cells. Upon diagnosis, immunoglobulin deposition within the biliary tree and hepatic parenchyma, as well as multi-organ manifestations of the more broadly termed “IgG4 related diseases” should be taken into clinical consideration. A trucut biopsy was initially indicated since fine needle aspiration (FNA) diagnostic yield was 43%. With the second generation FNB needle the use of trucut biopsy is not needed. First line therapy involves a course of corticosteroids that is typically tapered based on organ responsiveness. More recent case series include depletion of the B cell line with Rituximab for patient's refractory to steroids.