ISC is a rare disease, and its exact prevalence is not yet known. According to a previous report,10 a substantial portion (17%) of bile duct resection for presumed hilar CCC was finally proven not to be malignant, and significant lymphoplasmacytic infiltration was also identified histologically in half of those benign strictures. The prevalence of hilar or intrahepatic strictures as biliary manifestations ERK inhibitor of IgG4-related systemic disease in patients with AIP has been reported to be 8–13%11,12 to 46–49%.3,5 In our data, these proximal biliary strictures were observed only in 14% of patients with AIP (16/118). The wide range of prevalence of ISC in reports might be related

to the heterogeneity of the study population, including ethnic differences and undetermined natural courses of the disease, at which time, ISC develops along the clinical course of IgG4-related systemic disease in each individual patient. ISC can be preceded, accompanied, or followed by AIP.13 Among our patients, two patients exhibited a long disease interval gap between ISC and AIP, with ISC preceding AIP by 9 years, and ISC following AIP by 8 years. Concurrent AIP was

observed in one-third of patients with ISC (6/16). It is already well known that IgG4-positive cell infiltration in the bile duct specimen and serum IgG4 elevation are characteristic findings in ISC. Since ISC is a rare disease, however, it might not BMN673 be practical or cost-effective that serological evaluation for serum IgG4 and histological evaluation with IgG4 immunostaining selleck products are routinely

performed in all patients with hilar or intrahepatic biliary strictures. This strategy might be appropriate only when ISC is suspected clinically and radiologically. Our case series revealed several characteristic radiological findings, which were likely to be useful for differential diagnosis between ISC and hilar CCC. First, bile duct wall thickening, especially at the hilum, was prominent, but the luminal surface was smooth, with relatively preserved luminal patency. Thus, it looked like a doughnut (Fig. 2a). A plausible explanation for the smooth luminal surface and preserved luminal patency, despite marked bile duct wall thickening, could be that the bile duct epithelium is relatively intact, while the bile duct wall is thickened by extensive lymphoplasmacytic infiltration and fibrosis.14 In addition, the bile duct wall was a thickened in a concentric pattern in our patients with ISC,12 in contrast to the abrupt and eccentric strictures with a irregular surface in CCC.15 Second, proximal biliary dilatation was relatively mild in ISC, despite the marked bile duct wall thickening, in contrast to the marked proximal dilatation in CCC. Third, multifocal strictures with intervening normal-looking branches were observed in most of our ISC patients, in comparison to a single, localized stricture in CCC.