autoimmune hepatitis

Autoimmune hepatitis is classified into two types based on autoantibody profile: Type 1 (classic) is associated with ANA (antinuclear antibody) and/or anti-smooth muscle antibody (ASMA), occurs in adults and children, and is more common overall. Type 2 is associated with anti-liver/kidney microsomal antibody (anti-LKM1) and anti-liver cytosol antibody type 1 (anti-LC1), typically affects children, and can be more severe. Pathophysiology involves T-cell mediated autoimmune attack on hepatocytes, leading to interface hepatitis (piecemeal necrosis) on histology, with plasma cell infiltration being a hallmark finding. It is associated with other autoimmune diseases (thyroiditis, type 1 diabetes, celiac disease, ulcerative colitis) and HLA-DR3/DR4 haplotypes. Clinical presentation ranges from asymptomatic transaminase elevation to acute liver failure; symptoms include fatigue, jaundice, arthralgias, and amenorrhea. Labs show elevated AST/ALT (often >1000 in acute flares), elevated IgG, positive ANA/ASMA (type 1) or anti-LKM1 (type 2), and negative viral hepatitis serologies. Liver biopsy is essential for diagnosis and shows interface hepatitis with lymphoplasmacytic infiltrate. Treatment involves corticosteroids (prednisone) often combined with azathioprine, which induces remission in most patients; relapse is common upon drug withdrawal. Untreated or refractory disease can progress to cirrhosis and liver failure, requiring transplantation. It is important to distinguish AIH from primary biliary cholangitis and primary sclerosing cholangitis, though overlap syndromes exist. On USMLE, AIH is a classic cause of chronic hepatitis in young women with other autoimmune conditions, elevated IgG, and a dramatic response to steroids.