MRCP Appearance and Autoantibody Profile in IgG4-Related Sclerosing Cholangitis
On MRCP, IgG4-related sclerosing cholangitis characteristically shows long strictures with prestenotic dilatations, absence of peripheral duct pruning, and lack of biliary pseudodiverticula—features that help distinguish it from PSC. 1 ANA and AMA autoantibodies are not typically positive in IgG4-SC, as this is not a classic autoimmune disease but rather an IgG4-related fibroinflammatory condition. 1
MRCP Imaging Characteristics
Key Distinguishing Features from PSC
Long strictures with prestenotic dilatations are the hallmark MRCP finding in IgG4-SC, contrasting with the short band-like strictures of PSC 1
Absence of peripheral duct pruning helps differentiate IgG4-SC from PSC, where pruning is commonly seen 1
Lack of biliary pseudodiverticula further supports IgG4-SC over PSC 1
MRCP serves as the cornerstone non-invasive evaluation tool, defining pancreaticobiliary ductal anatomy and identifying other organ involvement with 90% sensitivity 2
Cholangiographic Patterns
IgG4-SC can be classified into four distinct cholangiographic types based on the location and pattern of biliary strictures 3
Biliary involvement occurs in >80% of IgG4-related pancreatitis cases, with characteristic patterns on cholangiography 2
Pancreatic ductal abnormalities such as long strictures and multifocal stricturing are present with 80% sensitivity 2
Important Diagnostic Caveat
Despite these characteristic features, a multicenter study demonstrated that even specialists have difficulty making a correct diagnosis by cholangiography alone, with high interobserver variation 1
Cholangiographic interpretation should never be used in isolation but must be combined with clinical, serological, and histopathological findings 1, 4
Autoantibody Profile
ANA and AMA Status
ANA (antinuclear antibodies) and AMA (anti-mitochondrial antibodies) are NOT characteristic features of IgG4-SC 1
These autoantibodies are more typical of other autoimmune liver diseases (AMA in primary biliary cholangitis, ANA in autoimmune hepatitis) but not IgG4-related disease 1
Relevant Serological Markers
Elevated serum IgG4 levels are found in 50-80% of IgG4-SC patients and represent the most relevant serological marker 2, 5
Serum IgG4 >4× upper limit of normal is highly specific for IgG4-SC 2, 5
An IgG4/IgG1 ratio >0.24 improves specificity for distinguishing IgG4-SC from PSC 2, 5
Blood IgG4/IgG RNA ratio >5% by quantitative PCR has excellent sensitivity (94%) and specificity (99%) 2
Critical Distinction
Elevated serum IgG4 alone is insufficient for diagnosis, as 9-15% of PSC patients also have elevated IgG4 levels 2
The diagnosis requires combination of imaging, serology, histopathology, and clinical context 1, 4, 6
Additional Diagnostic Clues
Associated Features Supporting IgG4-SC
Pancreatic involvement is present in >80% of cases, with pancreatic mass or enlargement on CT being highly suggestive 1
Low prevalence of inflammatory bowel disease (5.6%) compared to PSC (70%) is a key distinguishing feature 1, 7
Extrapancreatic manifestations involving salivary glands, kidneys, and retroperitoneum occur in 85% of cases 2
Dramatic response to corticosteroids occurs in 62-100% of cases within 2-4 weeks, unlike PSC which does not respond to steroids 2, 5