Autoimmune hepatitis (AIH) is a progressive inflammatory liver disorder preferentially affecting females and characterized serologically by high aminotransferase levels, elevated immunoglobulin G (IgG), and presence of autoantibodies and histologically by interface hepatitis in the absence of a known etiology. AIH is divided into two types according to the auto-antibody profile: patients with type 1 are positive for antinuclear antibody (ANA) and/or anti–smooth muscle antibody (ASMA); patients with type 2 are positive for anti–liver-kidney-microsomal antibody type 1 (anti-LKM-1). AIH responds satisfactorily to immunosuppressive treatment.
HISTORY AND EPIDEMIOLOGY
Autoimmune hepatitis is a relatively recently recognized disease, having been first described by Waldenström  in 1950. Seropositivity for ANA, the hallmark of systemic lupus erythematosus, led Mackay et al.  to call it lupoid hepatitis, a term no longer used. Because the disease frequently presents acutely, similarly obsolete is the term chronic active hepatitis, which implied that the disease should be chronic, that is, of at least 6 months' duration, before institution of immunosuppression. Before the efficacy of immunosuppression was established, untreated severe AIH had a mortality rate of 50% at 5 years and 90% at 10 years [3, 4]. The prevalence of AIH is unknown. Studies in adults have reported rates varying from 1 in 200,000 in the U.S. general population  to 20 in 100,000 in females over 14 years of age in Spain ; both figures are probably underestimates.