Autoimmune diseases of the liver and biliary tract and overlap syndromes in childhood.

Autoimmune liver diseases in childhood includes Autoimmune Hepatitis (AIH) and Primary (Autoimmune) Sclerosing Cholangitis (P(A)SC). Both diseases are characterized by a chronic, immune-mediated liver inflammation involving mainly hepatocytes in AIH and bile ducts in PSC. Both diseases, if untreated, lead to liver cirrhosis. AIH could be classified, according to the autoantibodies pattern, into two subtypes: AIH type 1 presents at any age as a chronic liver disease with recurrent flares occasionally leading to liver cirrhosis and liver failure. Characterizing autoantibodies are anti-nuclear (ANA) and anti-smooth muscle (SMA), usually at high titer (>1:100). These autoantibodies are not specific and probably do not play a pathogenic role. AIH type 2 shows a peak of incidence in younger children, however with a fluctuating course. The onset is often as an acute liver failure. Anti-liver kidney microsome autoantibodies type 1 (LKM1) and/or anti-liver cytosol autoantibody (LC1) are typically found in AIH type 2 and these autoantibodies are accounted to have a potential pathogenic role. Diagnosis of AIH is supported by the histological finding of interface hepatitis with massive portal infiltration of mononuclear cells and plasmocytes. Inflammatory bile duct lesions are not unusual and may suggest features of ''overlap'' with P(A)SC. A diagnostic scoring system has been developed mainly for scientific purposes, but his diagnostic role in pediatric age is debated. Conventional treatment with steroids and azathioprine is the milestone of therapy and it is proved effective. Treatment withdrawal however should be attempted only after several years. Cyclosporin A is the alternative drug currently used for AIH and it is effective as steroids. P(A)SC exhibit a peak of incidence in the older child, typically in pre-pubertal age with a slight predominance of male gender. Small bile ducts are always concerned and the histological picture shows either acute cholangitis (bile duct infiltration and destruction) and/or lesions suggesting chronic cholangitis as well (bile duct paucity and/or proliferation, periductal sclerosis). Small bile ducts damage may be associated, at onset or in the following years, with lesions of larger bile ducts with duct wall irregularities, strictures, dilations, and beading resulting in the characteristic ''bead-on-a-string'' appearance. The ''small duct'' (autoimmune) sclerosing cholangitis is also called autoimmune cholangitis. PSC is strictly associated to a particular form of inflammatory bowel disease (IBD) which shows features not typical of ulcerative colitis neither of Crohn's disease. Symptoms related to IBD often are present at onset (abdominal pain, weight loss, bloody stools) but the liver disease is frequently asymptomatic and it may be discovered fortuitously. Treatment of PSC is particularly challenging. In case of ''small duct'' SC or in case of evidence active inflammation on liver biopsy, immunosuppressive treatment is probably useful while in case of large bile ducts non inflammatory sclerosis, immunosuppression is probably uneffective. Ursodeoxycholic acid, however, may leads to an improvement of liver biochemistry even if there's no evidence that it may alter the course of disease. Thus, liver transplantation, is often necessary in the long term follow-up, even with a risk of disease recurrence. In adjunction to these two main disorders, many patients show an''overlap'' disease with features of both AIH and PSC. In such disorders the immune-mediated damage concerns both the hepatocyte and the cholangiocyte with a continuous clinical spectrum from AIH with minimal bile ducts lesions and PSC with portal inflammation and active inflammatory liver damage.