A New Great Mimicker: A Rare Case Of Igg4-Disease With Isolated Sclerosing Cholangitis

INTRODUCTION: Immunoglobulin G4-related disease (IgG4-RD) is a rare newly discovered systemic immune-mediated fibroinflammatory disease of unknown etiology that can involve multiple organs. IgG4-RD has a broad spectrum of entities. IgG4-related sclerosing cholangitis is the biliary manifestation of IgG4-RD, typically occurring together with type 1 AIP, but isolated IgG4-SC accounts for only 8% of IgG4-RD cases. Although the mainstay of IgG4-SC treatment is steroid (with and /or without immunosuppressants), but clinical studies are still scarce about this disease. CASE DESCRIPTION/METHODS: We present a rare and challenging case of a 60-year-old male who presented with steatorrhea and elevated liver enzymes without clinical signs of obstructive jaundice. Imaging revealed mild intrahepatic biliary ductal dilatation and mild wall thickening with no evidence of pancreatitis or mass. Esophagogastroduodenoscopy (EGD) and small bowel biopsy were unremarkable for malabsorption disorders. ERCP and EUS-FNA were inconclusive but excluded malignancy. However, a high index of suspicion for IgG4 has driven to check serology and surprisingly it has revealed a strongly elevated IgG4 level. The patient was started on steroid and later immunomodulator with subsequent clinical and serological improvement as well as resolution of the biliary ductal dilatation on imaging afterward.We here report a unique case of isolated IgG4-related sclerosing cholangitis with uncommon presentation and in the absence of AIP, diagnosed by clinical correlation, serology, response to steroids, and exclusion of other possible disorders. DISCUSSION: IgG4-RD is a newly recognized disease in the early 2000s, with unknown exact prevalence. The disease is difficult to diagnose and still does not have its own unique International Statistical Classification of Diseases and Related Health Problems (ICD)-10 code. IgG4-RD can mimic other autoimmune rheumatic diseases such as Sjögren's syndrome (SS), systemic lupus erythematosus (SLE), and granulomatosis with polyangiitis, as well as a number of other conditions. An isolated IgG4-SC may also mimic other conditions such as primary sclerosing cholangitis (PSC) and cholangiocarcinoma (CCA); therefore, physicians must carry a high index of suspicion for this under-recognized disease as IgG4-SC can respond to steroids in comparison to malignancy which is treated with surgical intervention. Early diagnosis and treatment are required to prevent irreversible fibrosis, biliary sepsis, and hepatic failure.Figure 1.: ERCP showing normal biliary tree with no focal lesions.