Challenges and difficulties in pathological diagnosis of autoimmune hepatitis.

Autoimmune hepatitis (AIH) with acute presentation is widely recognized as a distinct clinical entity, and its clinicopathology has been extensively studied. In most cases, AIH with acute presentation is merely acute exacerbation of classical chronic AIH, but pure acute-onset AIH without previous symptoms of chronic liver disease is also encountered. Rapid diagnosis and initiation of immunosuppressive treatment are necessary for both acute exacerbation and acute-onset to prevent fatal liver failure. The diagnostic criteria commonly used for classical AIH are generally applicable to acute exacerbation, but acute-onset AIH may present with additional pathological features. These features include an acute hepatitis phase characterized by centrilobular necrosis. However, centrilobular necrosis is also a feature of drug-induced liver injury, and there are no known histological characteristics exclusive to acute-onset AIH. Moreover, the possibilities of drug-induced AIH and immune-mediated drug-induced liver injury make diagnosis even more difficult. At present, liver biopsy is mandatory for the diagnosis of AIH with acute presentation, but careful consideration of all clinicopathological signs is necessary for differential diagnosis.