Immunoglobulin G4 (IgG4) Associated Cholangitis (IAC)
There is a group of patients with biliary strictures that respond well to or improve with steroid therapy. This condition is called Immunoglobulin G4 (IgG4) Associated Cholangitis (IAC). It can be difficult to distinguish from PSC and cholangiocarcinoma (bile duct cancer), and there is the suggestion that they might even overlap.
IgG4 is a type of antibody produced by the immune system to fight infection. In IAC this is overproduced and the disease is characterized by increased levels of of IgG4 in the blood and the presence of IgG4 secreting white blood cells (plasma cells) in the liver on biopsy. Unlike PSC, IAC is not usually associated with IBD but maybe associated with inflammation in the pancreas (pancreatitis) and other organs. IAC can be difficult to distinguish from PSC and cholangiocarcinoma but it is important to make the diagnosis because the disease responds extremely well to treatment with steroids, unlike most patients with PSC.
Separate conditions - IAC and PSC?
It is not clear whether IAC and PSC are separate conditions entirely or if they are variations on the same spectrum. There is the suggestion of an overlap between PSC and IAC because 9-36% of patients with PSC have increased serum IgG4 levels, and some have responded to steroid treatment, especially when younger.
It is recommended that all newly diagnosed PSC patients are tested for IgG4 levels.
Reviewed 10/05/12Bjornsson E, Chari ST, Smyrk TC, Lindor K. Immunoglobulin G4 associated cholangitis:description of an emerging clinical entity based on review of the literature. Hepatology 2007;45:1547-1554.