A Case of IgG 4 Seronegative Type I Autoimmune Pancreatitis

Abstract

Introduction IgG related diseases (IgG4-RD) are rather distinct autoimmune gastrointestinal conditions including autoimmune pancreatitis (AIP) and sclerosing cholangitis. Patients present with organomegaly or mass, lymphadenopathy, obstructive jaundice and weight loss. The most common extra-pancreatic finding of Type 1 AIP is IgG4 Sclerosing Cholangitis which resembles Primary Sclerosing Cholangitis or cholangiocarcinoma. Case 67 y.o male with PMH of GERD, presented with 2 wk H/O generalized abdominal discomfort, weight loss, fatigue and painless jaundice. Physical Exam: Vitals WNL and positive scleral icterus. Elevated LFTs, bilirubin and Ca 19-9 were detected with normal CEA. Total IgG: 12.9 and IgG4: 0.67. Autoantibody screen negative. CT Abd/pelvis showed mediastinal lymphadenopathy, bulky pancreatic head along with tiny foci of calcifications throughout and evidence of intra and extra-hepatic biliary dilatation. MRCP showed widespread intra-hepatic duct dilatation suggestive of PSC. ERCP showed 3cm stricture in CBD and biliary stricture involving both right and left hepatic ducts. Biopsy ruled out malignancy. Patient showed clinical and lab normalization after steroid therapy which was confirmed by normal internal MRCP. Based on this clinical response and radiological evidence, a seronegative AIP with extra-pancreatic IgG4 related SC was diagnosed. Discussion Type 1 AIP, the prototype of IgG4RD is prevalent worldwide, typically affecting middle aged and older men. Sensitivity and specificity of seropositive AIP have been found to be as low as 62% and 59% respectively and studies show IgG4 seronegativity in as many as 24% cases. Despite lack of serological and histological evidence, AIP with IgG4 related SC can still be diagnosed based on history, imaging and therapeutic response as also suggested by International Consensus Diagnostic Criteria (ICDC). Conclusion: This case stresses the advantage of timely identification and treatment of seronegative IgG4 AIP and SC. Normal IgG4 levels and lack of definite histology shouldn't exclude the diagnosis when there are characteristic clinical findings and extra-pancreatic manifestations, along with distinctive imaging results. It is imperative to treat patients with steroid trial and close clinical monitoring to avoid unnecessary pancreatobiliary procedures.