A rare case of type 1 autoimmune pancreatitis combined with a pancreatic neuroendocrine tumor.

Abstract

Type 1 autoimmune pancreatitis (AIP) is seen as a pancreatic manifestation of immunoglobulin G4-related disease (IgG4-RD), histopathologically characterized by infiltration of IgG4 positive lymphoplasmacytes, obliterative phlebitis and storiform fibrosis.1 Despite many guidelines for AIP being established in recent years, differentiating between AIP and pancreatic neoplasm is still challenging in some atypical cases, especially in locally enlarged pancreatic tumors. A 71-year-old man with regular postoperative follow-up for jejunal gastrointestinal stromal tumor resected 6 years previously was found to have a significant growth of 3.5 cm mass in the tail of the pancreas, calcification of the pancreas, and slight dilatation of bile duct while undergoing contrast-enhanced abdominal computed tomography (CT) scan (Figure 1A). There were no signs of fever, abdominal pain, diarrhea, and jaundice, but body weight loss of 7% (5 kg) within 6 months was noted. Routine laboratory analysis revealed only mild hyperbilirubinemia (total bilirubin 1.54 mg/dl). Given the rapid tumor growth within 2 years and considered pancreatic malignant neoplasm, laparoscopic distal pancreatectomy and splenectomy were performed. Histopathological examination showed storiform fibrosis and dense lymphoplasmacytic infiltration with increased number of IgG4-positive plasma cells up to 150 per high power field (Figures 1B,C), consistent with type 1 autoimmune pancreatitis. Besides, a small tumor sized 0.4 cm was accidently found during microscopic examination, which demonstrated pancreatic neuroendocrine microadenoma with mitotic activity of 0–1/10 HPF, 2% Ki-67-positive cells and positive immunohistochemical stain of synaptophysin, chromogranin A and insulinoma-associated protein 1. Taken all together, the clinical and histopathological features suggested a diagnosis of type 1 AIP and nonfunctional pancreatic neuroendocrine tumors (grade 1). The patient thereafter started corticosteroid treatment for type 1 AIP after surgical wound recovery and was regularly followed up at the outpatient department. The number of patients with AIP is still relatively small although reports have increased in recent years with an overall prevalence rate of 10.1 per 100,000 people, mainly affecting the elderly with male predominance.2 The clinical features are generally abdominal pain and painless obstructive jaundice, with some of those affected being even asymptomatic.3 AIP is related to typical radiological images, including pancreatic enlargement with delayed enhancement and main pancreatic duct narrowing; abnormal serologic markers, including elevation of IgG, IgG4 or presence of autoantibodies; and histopathological features including fibroinflammatory change and infiltration of lymphocytes and plasma cells. Abdominal CT is regarded as a modality in a differential diagnosis between AIP and pancreatic cancer; however, the focal form of AIP reveals localized enlargement or mass-like lesion in the pancreas with delayed enhancement, thereby making it difficult to distinguish AIP from a pancreatic malignant neoplasm.1, 3 In cases with AIP, the incidence of pancreatic cancer at or after the diagnosis of AIP is approximately 1.7%,2 suggesting that the confirmed diagnosis of AIP cannot exclude the coexistence of pancreatic malignant neoplasm. For differential diagnosis, endoscopic ultrasonography-guided fine needle aspiration is a choice to validate identification.4 In patients with nonfunctional pNET <2 cm, routine surgical intervention is not recommended, although for patients with pNET >2 cm, tumor resection remains indicated,5 but in contrast, glucocorticoid is recommended when AIP diagnosed. In conclusion, AIP is an IgG4-RD of the pancreas with low prevalence compared to pancreatic cancer, although misdiagnosis of these diseases occurs especially in focal AIP. We herein report a rare case of histopathologically proven AIP where the lesion was combined with a small pNET. Not only pancreatic cancer, but pNET may also co-occur with AIP. All authors declare no conflict of interest.