AB1571 IGG4-RELATED AUTOIMMUNE PANCREATITIS MIMICKING PANCREATIC CARCINOMA

Abstract

BackgroundIgG4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder characterized by dense infiltration of IgG4-positive plasma cells in the affected tissue. The inflammatory infiltration along with storiform fibrosis can lead to the development of tumefactive lesions that may affect any organ. Type 1 Autoimmune pancreatitis (AIP) is a rare presentation of IgG4-RD that can present as a pancreatic mass and may mimic pancreatic carcinoma.ObjectivesThe elevation of CA 19-9 is seen in autoimmune pancreatitis as well as pancreatic carcinoma. Therefore, it becomes difficult to differentiate between the two, especially in the presence of an elevated IgG4 level in the serum. We describe a rare instance of IgG4-related AIP with significantly high CA 19-9 levels.MethodsCase report.ResultsOur patient is a 65-year-old male with past medical history of IgG-4 related retroperitoneal fibrosis, who presented with the complaint of worsening right upper quadrant abdominal pain, jaundice, and weight loss.Labs showed WBC count 13.7 (4.0-9.0 x 10*3/uL) and eosinophil count 700 (50-300/cmm). ESR 94 (0-15 mm/hr) and CRP 57.9 (0-10 mg/dL). LFTs showed elevated total bilirubin 12.5 (0.1-0.2 mg/dL), alkaline phosphatase 620 (30-115 IU/L), AST 72 (5-45 IU/L), and normal ALT 52 (5-60 IU/L). Absolute CD4 count was 1152 (332-1642 cells/cmm), CD4 percentage was 80% (28-62%), CD4 to CD8 ratio was high 8.86 (0.7-4.8). CA 19-9 was elevated to 2830 (0-35 U/ml). IgG4 was elevated 162 (2-96 mg/dL).MRCP showed multiple biliary strictures and dilation of the main pancreatic duct. ERCP with stent placement was done to relieve biliary obstruction. EUS showed mass-like enlargement of the pancreatic head with atrophy, around the common bile duct (CBD). Biopsy of the CBD showed inflamed glandular mucosa, negative for malignancy. Pancreatic head biopsy showed normal stroma and benign mucosa, negative for malignancy. Patient had gradual improvement in bilirubin and CA 19-9 levels after ERCP and stent placement. He was started on prednisone which was followed by rituximab infusions. He followed up with rheumatology and had significant improvement in his symptoms and labs including a decrease in bilirubin to 2.8 mg/dL, alkaline phosphatase to 300 IU/L, and CA 19-9 levels to 100 U/ml within 1 month of discharge.ConclusionAutoimmune pancreatitis (AIP) can be difficult to distinguish from pancreatic carcinoma. High levels of CA 19-9 are usually indicative of malignancies, whereas high levels of IgG4 are characteristic of AIP. As per Van et al., the measurement of either CA 19-9 or IgG4 level alone is not accurate enough for diagnosis. However, the combination of CA 19-9 < 74 U/ml and IgG4 > 1.0 g/L distinguishes patients with AIP from patients with pancreatic carcinoma with 94 % sensitivity and 100 % specificity [1]. CA 19-9 levels can also be elevated in other GI diseases including primary sclerosing cholangitis, bacterial cholangitis, or choledocholithiasis. Differentiation between these conditions is extremely important due to the vastly different treatments and the morbidity/mortality associated with them [2,3].IgG4-RD causing biliary obstruction with CA 19–9 elevation is a diagnostic dilemma. It can be misdiagnosed as pancreatic or cholangiocarcinoma. Our patient illustrates that IgG4-RD pseudotumors can significantly elevate CA 19-9. In these cases, further testing and biopsy should be performed to rule out malignancy.