[Adult Gianotti-Crosti syndrome caused by hepatitis B]

A 42-year-old man was admitted to our hospital with a lower extremity rash, general fatigue, and abdominal discomfort. Laboratory findings revealed elevated serum transaminases as well as positivity for the hepatitis B surface antigen and the immunoglobulin M type anti-hepatitis B core antibody. He was diagnosed with a rash typical of Gianotti-Crosti syndrome due to acute infection with hepatitis B virus, genotype A. After admission, the rash gradually decreased; however, serum transaminases and jaundice increased. Entecavir therapy was initiated on day 11 of admission, and his liver function subsequently improved over two weeks. Gianotti-Crosti syndrome is rarely seen in adult patients. It may be important to pay attention to the typical rash of Gianotti-Crosti syndrome because it may provide an important clue to an otherwise asymptomatic acute hepatitis B infection.