Diagnosis of IgG4‑Related Sclerosing Cholangitis

MRCP Imaging Features

On MRCP, IgG4‑SC shows long biliary strictures with pre‑stenotic dilatation, while primary sclerosing cholangitis (PSC) typically presents with short, band‑like strictures. This distinction is a key imaging hallmark. 1
Absence of peripheral duct pruning on MRCP helps separate IgG4‑SC from PSC, where pruning is common. 2
Lack of biliary pseudodiverticula further supports a diagnosis of IgG4‑SC over PSC. 1
MRCP provides a 90 % sensitivity for delineating pancreatic‑biliary anatomy and detecting extra‑biliary organ involvement, making it the cornerstone non‑invasive evaluation tool. 3
A multicenter study demonstrated high inter‑observer variation among specialists interpreting cholangiography alone, indicating limited reliability of imaging in isolation. 1

Elevated serum IgG4 is found in 50–80 % of patients with IgG4‑SC and is the most relevant serologic marker for this disease. 3
A serum IgG4 level > 4 × the upper limit of normal is highly specific for IgG4‑SC. 4
An IgG4/IgG1 ratio > 0.24 improves specificity when distinguishing IgG4‑SC from PSC. 3
Quantitative PCR detecting a blood IgG4/IgG RNA ratio > 5 % yields 94 % sensitivity and 99 % specificity for IgG4‑SC. 3
Elevated serum IgG4 alone is insufficient for diagnosis, as 9–15 % of PSC patients also have raised IgG4 levels. 3

Antinuclear antibodies (ANA) and anti‑mitochondrial antibodies (AMA) are not characteristic of IgG4‑SC and are usually negative. 2

Pancreatic involvement occurs in > 80 % of IgG4‑SC cases; a pancreatic mass or enlargement on CT is highly suggestive. 1
Inflammatory bowel disease is present in only ≈ 5.6 % of IgG4‑SC patients versus ≈ 70 % in PSC, providing a useful distinguishing feature. 1
Extrapancreatic manifestations (e.g., salivary‑gland, renal, retroperitoneal involvement) are observed in ≈ 85 % of patients. 3
Corticosteroid therapy leads to a dramatic clinical and radiologic response in 62–100 % of IgG4‑SC patients within 2–4 weeks, a response not seen in PSC. 4

Tissue diagnosis should aim for > 10 IgG4‑positive plasma cells per high‑power field and an IgG4⁺/IgG⁺ ratio > 40 %, which provide strong diagnostic evidence. 1
Ampullary biopsy with IgG4 immunostaining is positive in 52–72 % of IgG4‑SC cases and helps differentiate it from PSC. 2

Because imaging alone shows high inter‑observer variability, cholangiographic findings must be interpreted together with clinical presentation, serology, and histopathology to reach a definitive diagnosis of IgG4‑SC. 1

PSC is the most important condition to differentiate from IgG4‑related sclerosing cholangitis when biliary disease is present【5】.
Elevated serum IgG4 is found in approximately 9–15 % of patients with PSC, limiting the utility of IgG4 levels alone for distinction【5】.
An IgG4/IgG1 ratio greater than 0.24 improves specificity for distinguishing IgG4‑SC from PSC【5】.
Serum IgG4 exceeding 4 times the upper limit of normal is highly specific for IgG4‑SC compared with PSC【5】.

Pathological features of IgG4‑SC are identified in up to 8 % of patients undergoing surgery for presumed hilar CCA, making CCA a critical malignant differential【5】.
A blood IgG4/IgG RNA ratio > 5 % measured by quantitative PCR provides excellent diagnostic performance (sensitivity ≈ 94 %, specificity ≈ 99 %) for separating IgG4‑RD from CCA【5】.

Serum IgG4 is elevated in roughly 50–80 % of patients with IgG4‑RD, but the test alone cannot confirm the diagnosis【5】.

PET scanning can reveal fluorodeoxyglucose uptake at distant sites, a pattern characteristic of multisystem IgG4‑RD【5】.

Pursuing tissue diagnosis whenever feasible is essential to avoid missing malignancy, particularly cholangiocarcinoma, in patients with suspected IgG4‑SC【5】.

Normal serum IgG4 does not exclude IgG4‑RD, as 20–50 % of patients with the disease have IgG4 levels within the reference range【5】.