Extrahepatic bile ducts are the most commonly involved extrapancreatic organ site in patients with type 1 autoimmune pancreatitis. IgG4-related sclerosing cholangitis (IgG4-SC) alone, without evidence of pancreatic or other organ involvement, is uncommon and is difficult to distinguish from cholangiocarcinoma preoperatively. We describe 9 patients with isolated IgG4-SC over an approximate 10-year period, each clinically suspected to have cholangiocarcinoma. We examined the clinical, radiological, cytologic (including fluorescence in situ hybridization results), and histologic features. IgG and IgG4 immunohistochemistry were performed. All 9 patients were middle-aged men who presented with obstructive jaundice. The biliary strictures involved all parts of the extrahepatic biliary tree. Serum IgG4 was slightly elevated in three of eight patients. Cytologic findings were interpreted as negative in six, atypical in one, and suspicious for adenocarcinoma in one. Fluorescence in situ hybridization revealed aneuploidy in one and was equivocal (trisomy 7) in 2. Eight of 9 patients underwent radical resection for suspected cholangiocarcinoma. There was only one case diagnosed with IgG4-SC preoperatively based on biopsy. Histologic sections revealed a prominent lymphoplasmacytic infiltrate with storiform fibrosis and marked increased IgG4-positive plasma cells (≥30/high-power field) in all specimens. Fifty percent of cases (4/8) had IgG4/IgG plasma cell ratio >40%. On median follow-up of 2.8 years, no relapse has occurred in any patient. Extrahepatic IgG4-SC may present as an isolated lesion mimicking cholangiocarcinoma. The diagnosis can be challenging. Clinicians and pathologists should recognize this to avoid major surgery.
Keywords: Autoimmune pancreatitis; IgG4; IgG4-related disease; Inflammatory pseudotumor; Sclerosing cholangitis.
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