A 31-year-old woman has experienced increasing malaise for the past 4 months. Physical examination yields no remarkable findings. Laboratory studies show total serum protein of 6.4 g/dL, albumin of 3.6 g/dL, total bilirubin of 1.4 mg/dL, AST of 67 U/L, ALT of 91 U/L, and alkaline phosphatase of 99 U/L. Results of serologic testing for HAV, HBV, and HCV are negative. Test results for ANA, anti-liver kidney microsome-1 and anti-smooth muscle antibody are positive. A liver biopsy is done; microscopically, there are minimal portal mononuclear cell infiltrates with minimal interface hepatitis and mild portal fibrosis. What is the most likely diagnosis?

Autoimmune hepatitis is a chronic liver disease of unknown cause in which antibodies to hepatocyte structural components cause progressive necrosis of hepatocytes, leading to cirrhosis and liver failure. Patients tend to improve with glucocorticoid therapy. a1 -Antitrypsin deficiency and Wilson disease can lead to chronic hepatitis and cirrhosis, but autoimmune markers are absent. Chronic alcoholism is not associated with the formation of autoantibodies. Because this patient does not have evidence of HBV infection, there can be no superinfection with HDV. Isoniazid may cause acute or chronic hepatitis, but without autoantibodies. Patients with primary biliary cirrhosis often have antimitochondrial antibody (which also can be seen in autoimmune hepatitis), but the bilirubin concentration and alkaline phosphatase level would be much higher in primary biliary cirrhosis.