Clinical Characteristics Of Autoimmune Pancreatitis And Its Differential Diagnosis From Pancreatic Cancer

OBJECTIVE:Autoimmune pancreatitis (AIP) is a special type of chronic pancreatitis, which may misdiagnosed as pancreatic carcinoma. This study aims to determine the clinical characteristics of AIP and describe a strategy to differentiate it from pancreatic cancer using a combination of clinical, serological, radiology, and histopathological features.METHODS:A retrospective study was performed among the patients with AIP and pancreatic cancer presenting in The First Affiliated Hospital, Zhejiang University School of Medicine, China between November2009and April2014. Data of general conditions, clinical symptoms, serum markers, radiological findings, pathological results and treatment was collected for further statistically analysis. All the cases with AIP were based on the International Consensus Diagnostic Criteria in2010and the diagnosis of pancreatic cancer was confirmed by pathology.RESULTS:(1) Both occuring predominantly in elderly males, gender differences in the two groups was not significant, while the age was older in AIP group. Abdominal pain, obstructive jaundice and weight loss were the most common symptoms in patients with AIP, while in patients with pancreatic cancer, abdominal pain, abdominal distention and weight loss were often observed. The clinical manifestations were very similar in the two groups and56%of out-patients with AIP were misdiagnosed as pancreatic cancer.(2) Other organ involvement was characteristic clinical manifestation in AIP, patients with AIP who presented extrapancreatic lesions were up to50%.(3) AIP was characterized by incresed serum levels of immunoglobulin IgG and IgG4. Serum levels of Globulin, eosinophils, bilirubin, hepatic and biliary enzymes in AIP group were significantly higher than those in pancreatic cancer group(P<0.05), while tumor marker CA19-9and hemoglobin levels were significantly lower (P<0.05). The combination of CA19-9, globulin, hemoglobin and eosinophils identified patients with AIP with84%sensitivity and88%specificity, which indicated relatively high diagnostic value.(4) Ultrasound and CT were the most commonly used imaging tools in AIP and pancreatic cancer. MRCP and ERCP were effective for detecting pancreatic and biliary duct lesions. A diffusely enlarged pancreas strongly suggested AIP. However,40%of AIP also presented with segmentally/focally enlarged pancreas, which must be distinguished from pancreatic cancer. Upstream dilatation of the bile duct and lower narrowing were observed more frequently in AIP group than pancreatic cancer group, while dilatation above the narrowed area upstream of the main pancreatic duct often suggested pancreatic cancer. Part of the AIP cases presented effusion or capsule-like rim around the autoimmune pancreatitis lesions. Peripheral vascular involvement, lymphnode and other organ metastasis were characteristic of pancreatic cancer.(5) Histopathologic findings were strong evidence for the differential diagnosis of AIP and pancreatic cancer. Severe lymphoplasmacytic infiltration, especially IgG4-positive plasma cell infiltrations and storiform fibrosis were characteristic histological findings in AIP. Diagnosis of pancreatic cancer by pathological findings may be confirmed by histological identification of carcinoma cells.(6) Steroid therapy was effective for AIP. Prior to steroid therapy, patients with obstructive jaundice due to biliary obstruction should be managed by therapeutic ERCP with endobiliary stent placement and/or endoscopic nasobiliary drainage. Relapse and re-hospitalization happened in12%of the AIP patients during a period of1-2years. Pancreatic cancer patients received radical surgery or alleviative treatment depending on the stage of malignancy. CONCLUSION:Regarded as two separate entity, the treatment and prognosis of AIP and pancreatic carcinoma were completely different. Similarity of epidemiology and clinical manifestations made it difficult to distinguish AIP from pancreatic cancer. A combination of extrapancreatic organ involvement, serological, radiological and histopathological features could help differentiating between these diseases.