A 50-year-old woman presents with progressive jaundice, weight loss, and a CA 19-9 of 890 U/mL. MRCP shows a diffusely dilated intrahepatic bile duct with a soft-tissue mass at the hepatic hilum. She is found to have IgG4 serum level of 650 mg/dL. A biopsy shows storiform fibrosis, obliterative phlebitis, and >10 IgG4-positive plasma cells per HPF. Which diagnosis most changes her management?

• A Perihilar cholangiocarcinoma (Klatskin tumor) — requiring surgical resection
• B Primary sclerosing cholangitis with malignant transformation — requiring liver transplant evaluation
• C Carcinoma of gallbladder with hilar involvement — requiring radical cholecystectomy
• D IgG4-related sclerosing cholangitis (type 1 autoimmune pancreatitis-associated biliary disease) — steroid responsive ✓

Explanation

IgG4-related sclerosing cholangitis (IgG4-SC), often concurrent with type 1 autoimmune pancreatitis, can mimic perihilar cholangiocarcinoma with obstructive jaundice and elevated CA 19-9. Key diagnostic features are: serum IgG4 >135 mg/dL (here markedly elevated), storiform fibrosis, obliterative phlebitis, and >10 IgG4-positive plasma cells per HPF on biopsy — the HISORt criteria. This diagnosis is critical because IgG4-SC is steroid-responsive (prednisolone 0.6 mg/kg/day) and does not require surgery, whereas cholangiocarcinoma requires resection. Misdiagnosing IgG4-SC as cholangiocarcinoma leads to unnecessary major surgery.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.