Diagnostic Criteria

Elevated serum IgG4 levels support but cannot definitively diagnose IgG4-RD, with serum IgG4 elevated in 50-80% of patients with IgG4-RD 1, 2, 3
Serum IgG4 >4× upper limit of normal is highly specific for IgG4-related sclerosing cholangitis, although this fact is from a less preferred source, a more relevant fact is: An IgG4/IgG1 ratio >0.24 improves specificity for distinguishing IgG4-SC from PSC 2, 4
Blood IgG4/IgG RNA ratio >5% by quantitative PCR has excellent sensitivity (94%) and specificity (99%) 2, 3
Elevated serum IgG4 alone is insufficient for diagnosis, as 9-15% of PSC patients also have elevated levels 1, 2
The American Gastroenterological Association recommends that tissue diagnosis should be pursued whenever possible to distinguish IgG4-RD from malignancy and other inflammatory conditions, with specific quantitative criteria including >10 IgG4-positive plasma cells per high-power field in biopsy specimens 1, 5, 6
The American Gastroenterological Association also recommends that IgG4+/IgG+ plasma cell ratio >40% provides additional diagnostic evidence 5, 7

Imaging Criteria

Non-invasive imaging with CT, MRI/MRCP is the cornerstone of evaluation, identifying organ involvement and characteristic biliary patterns in IgG4-related sclerosing cholangitis 1, 3, 5, 8
PET scanning may identify fluorodeoxyglucose uptake at distant sites characteristic of multisystem disease 1, 3

Treatment Options

The American College of Gastroenterology recommends that corticosteroids are the first-line treatment for active IgG4-RD, with dosing regimen including initial dose of prednisolone 0.6 mg/kg/day orally for 2-4 weeks, tapering gradually to maintenance dose of 2.5-5 mg/day over 2-3 months 9
The American College of Gastroenterology also recommends that all patients with IgG4-RD should be considered for continued immunosuppressive therapy due to the high relapse rate, with options for maintenance therapy including azathioprine, mercaptopurine, mycophenolate, and maintenance prednisolone 5-7.5 mg daily 9, 10
Rituximab is the preferred treatment for steroid-refractory disease or disease that flares on steroid withdrawal, with dosing of 2 infusions of 1000 mg rituximab 15 days apart, repeated every 6 months for maintenance 9, 10

Clinical Presentation and Diagnosis

The American Gastroenterological Association recommends considering IgG4-related pancreatitis in patients with obstructive jaundice, diffuse pancreatic enlargement, and weight loss, as these symptoms are present in 80% of cases with elevated IgG4 11
Extrapancreatic manifestations, including involvement of salivary glands, kidneys, retroperitoneum, and biliary tree, occur in 85% of cases with elevated IgG4, supporting the diagnosis of IgG4-related disease 11
Pancreatic ductal abnormalities on MRCP, such as long strictures and multifocal stricturing, are characteristic of IgG4-related pancreatitis, with a sensitivity of 80% 12, 13
Biliary involvement, including IgG4-related sclerosing cholangitis, occurs in >80% of cases, with four characteristic patterns on cholangiography, and is a key diagnostic feature 12, 13

Diagnostic Approach

The European Society of Gastrointestinal Endoscopy recommends using MRI/MRCP as the cornerstone of non-invasive evaluation, defining pancreaticobiliary ductal anatomy and identifying other organ involvement, with a sensitivity of 90% 12, 13
Histological confirmation should always be pursued to exclude malignancy and confirm IgG4-related disease, with a cutoff of >10 IgG4-positive plasma cells per high-power field in biopsy specimens, providing a sensitivity of 84% and specificity of 100% 12, 14
The IgG4+/IgG+ plasma cell ratio >40% provides additional diagnostic evidence, with a positive predictive value of 95% 12

Management Approach

The American College of Gastroenterology recommends corticosteroids as the definitive first-line therapy, with a characteristic prompt clinical and radiographic response occurring in 62-100% of cases, and a response rate of 90% within 2-4 weeks 11
Maintenance therapy with immunosuppressive agents, such as azathioprine or mycophenolate, should be considered in all patients due to relapse rates exceeding 40%, with a median time to relapse of 12 months 11
Rituximab is the preferred treatment for steroid-refractory disease or disease that flares on steroid withdrawal, with a response rate of 80% and a median duration of response of 18 months 15

Guideline Recommendations for Diagnosis and Management of IgG4‑Related Autoimmune Pancreatitis

Diagnostic Imaging

Magnetic resonance cholangiopancreatography (MRCP) is the preferred modality to evaluate IgG4‑related sclerosing cholangitis, revealing characteristic long strictures with pre‑stenotic dilatation, absence of peripheral duct pruning, and lack of biliary pseudodiverticula. 16
Endoscopic ampullary biopsy with IgG4 immunostaining should be performed when MRCP findings are suggestive, as IgG4 positivity is observed in 52–72 % of IgG4‑related sclerosing cholangitis cases, supporting the diagnosis. 16
Contrast‑enhanced CT or MRI of the abdomen and pelvis is recommended to screen for renal parenchymal lesions and retroperitoneal fibrosis, which are common extrapancreatic manifestations of IgG4‑related disease. 16

Histopathologic Criteria

When tissue is obtained, diagnosis should be confirmed by the presence of >10 IgG4‑positive plasma cells per high‑power field and an IgG4⁺/IgG⁺ cell ratio >40 %, helping to distinguish IgG4‑related disease from malignancy. 16

Differentiation from Primary Sclerosing Cholangitis (PSC)

Inflammatory bowel disease (IBD) is a key discriminating feature: it occurs in approximately 70 % of PSC patients but only about 5.6 % of patients with IgG4‑related sclerosing cholangitis. 16
Unlike PSC, IgG4‑related disease shows a rapid and dramatic response to corticosteroids, with improvement in symptoms, laboratory markers, and imaging within 2–4 weeks in 62–100 % of cases, whereas PSC does not respond to steroids. 16

Steroid Therapy Monitoring

Long‑term corticosteroid therapy requires vigilant monitoring for adverse effects, as steroid‑related complications are common during prolonged treatment. 17

Distinguishing IgG4‑Related Sclerosing Cholangitis from Primary Sclerosing Cholangitis

Clinical Associations

Inflammatory bowel disease (IBD) is present in ~70 % of patients with primary sclerosing cholangitis (PSC) but only in ~5.6 % of patients with IgG4‑related sclerosing cholangitis (IgG4‑SC), making IBD the most important clinical discriminator between the two diseases 18, 19.
IgG4‑SC co‑exists with autoimmune pancreatitis in >80 % of cases, typically manifesting as a pancreatic mass or enlargement on cross‑sectional imaging 18.
Extrapancreatic IgG4‑related manifestations (e.g., salivary‑gland, renal, retroperitoneal involvement) occur in ~85 % of IgG4‑SC patients and are absent in PSC 18.

Demographic Differences

PSC predominantly affects younger adults, whereas IgG4‑SC tends to present in older individuals 18.
Both diseases show a male predominance, which is more pronounced in IgG4‑SC 18.

Imaging Characteristics (MRCP / Cholangiography)

IgG4‑SC characteristically shows long biliary strictures with upstream (pre‑stenotic) dilatation 18, 19.
The absence of peripheral duct “pruning” on cholangiography helps differentiate IgG4‑SC from PSC 18, 19.
Lack of biliary pseudodiverticula favors IgG4‑SC over PSC 18, 19.
A multicenter study demonstrated that even expert hepatobiliary radiologists have high inter‑observer variability and cannot reliably distinguish IgG4‑SC from PSC by cholangiography alone 18.

Histopathological Criteria

The presence of >10 IgG4‑positive plasma cells per high‑power field and an IgG4⁺/IgG⁺ ratio >40 % provides strong diagnostic evidence for IgG4‑SC 18.
Endoscopic ampullary biopsy with IgG4 immunostaining is positive in 52‑72 % of IgG4‑SC cases and aids differentiation from PSC 18, 19.
IgG4‑positive lymphoplasmacytic infiltrates may be seen in PSC liver biopsies but rarely reach the quantitative thresholds observed in IgG4‑SC 18, 19.

Treatment Response (Definitive Discriminator)

IgG4‑SC exhibits a rapid clinical and radiographic response to corticosteroids in 62‑100 % of patients within 2‑4 weeks 18, 19.
Recommended induction regimen: prednisolone 40 mg daily (≈0.6 mg/kg/day) for 2‑4 weeks, followed by tapering of 5 mg per week over 8‑12 weeks 18.
PSC does not demonstrate a sustained response to corticosteroids 18.
In a cohort of 285 PSC patients with elevated IgG4 treated with steroids, 90 % showed initial bilirubin improvement but 50 % subsequently relapsed, and steroid‑related complications were common 18, 19.

Diagnostic Algorithm (Key Steps Supported by Evidence)

Diagnostic Approach to Suspected IgG4‑Related Sclerosing Cholangitis

Serologic Evaluation

In patients with biliary strictures and pancreatic duct abnormalities, total IgG, antinuclear antibody (ANA), anti‑mitochondrial antibody (AMA), and smooth‑muscle antibody should be measured concurrently to exclude overlap syndromes such as autoimmune hepatitis or primary biliary cholangitis. 20
Elevated serum IgG4 is observed in approximately 9–15 % of individuals with primary sclerosing cholangitis (PSC), indicating that an isolated IgG4 rise cannot definitively confirm IgG4‑related disease. 20

Histologic Criteria for IgG4‑Related Sclerosing Cholangitis

Endoscopic ampullary biopsy performed during ERCP demonstrates IgG4‑positive staining in 52–72 % of confirmed IgG4‑related sclerosing cholangitis cases, supporting its use as a diagnostic tissue source. 21
The histologic definition of IgG4‑related cholangitis requires >10 IgG4‑positive plasma cells per high‑power field and an IgG4⁺/IgG⁺ ratio > 40 %. 21
During ERCP, an ampullary biopsy with an IgG4 immunostain using the cut‑off of ≥10 IgG4‑positive cells per high‑power field is recommended to aid diagnosis. 21

Endoscopic Tissue Acquisition

ERCP should be employed only for tissue acquisition or therapeutic intervention, not as a first‑line diagnostic imaging test, according to current guideline recommendations. 20
When ERCP is performed, adding endobiliary forceps biopsies to brush cytology increases diagnostic yield, especially for biliary strictures that are ≥30 mm in length. 21
For patients with accessible retroperitoneal lymphadenopathy, EUS‑guided fine‑needle aspiration is advised because it provides a high diagnostic yield for extrinsic biliary compression caused by lymph node involvement. 21