[Autoimmune hepatitis and overlap syndrome: diagnosis].

Autoimmune hepatitis (AIH) is a rare autoimmune disease (incidence about 5% among all chronic liver disorders) that reflects a loss of tolerance to normal hepatic proteins. AIH is characterized by female preponderance, hypergammaglobulinemia, extrahepatic syndromes and a good response to immunosuppressive treatment. AIH may be subdivided into two or three subtypes. AIH type 1 is characterized by antinuclear autoantibodies (ANA) and/or smooth muscle antibodies (SMA). SMA are actin-specific, can occur without ANA and their presence relates strongly to AIH. AIH type 2 is defined by the presence of anti-liver-kidney microsomal antibodies (LKM-1). Patients with AIH type 2 are typically younger at the time of disease onset, exhibit higher inflammatory activity, suffer more frequent relapses under immunosuppressive treatment and are more likely to progress to cirrhosis. AIH type 3 is characterized by autoantibodies against the soluble liver antigen (SLA) and liver-pancreas antigen (LP), but ANA/SMA are frequently present and, therefore, some authors consider this autoantibody manifestation as belonging to AIH type 1. Antineutrophil cytoplasmic antibodies (ANCA) recognize cytoplasmic or nuclear components of neutrophilic granulocytes and are detected with high prevalence in patients with autoimmune liver diseases. They are associated with AIH type 1 but not with AIH type 2. However, 40-70% of patients with primary sclerosing cholangitis (PSC) also produce these autoantibodies. Autoimmune cholangitis is an idiopathic disorder with mixed hepatocellular and cholestatic findings that typically has antinuclear antibodies (ANA). It may be considered as an atypical form of primary biliary cirrhosis. It has been recognized that some forms of AIH may also occur with variable incidence and severity especially in patients with primary biliary cirrhosis (overlap AIH/PBC) or primary sclerosing cholangitis (AIH/PSC). On the basis of clinical, biochemical, serological, histological and radiological criteria a clear distinction between these conditions can be readily made in the majority of cases. An association of AIH-typical autoantibodies (anti-LKM-1, anti-SLA/LP) in association with antimitochondrial autoantibodies (AMA) almost confirm the overlap syndrome AIH/PBC. In PSC patients expressing typical ERCP findings and suffering from inflammatory bowel disease (IBD), the diagnosis of an overlap syndrome between PSC/AIH can be readily made in the presence of ANCA and AIH relevant autoantibodies. Apart from this kind of overlap syndrome involving different types of autoimmune disorders within the liver AIH can be also associated with other organspecific autoimmune disorders as documented in the autoimmune polyglandular syndrome type 1 (APS-1). In this disease homozygosity for a defect in a single gene (AIRE) leads to a broad spectrum of organ specific autoimmune diseases.