Current status and agenda in the diagnosis of nonalcoholic steatohepatitis in Japan

Nonalcoholic fatty liver disease (NAFLD), a manifestation of metabolic syndrome, includes a wide range of clinical entities from simple fatty liver, a benign condition, to nonalcoholic steatohepatitis (NASH), a condition which can progress to cirrhosis, hepatocellular carcinoma and hepatic failure. The diagnosis of NASH requires no history of previous or current significant alcohol consumption and no evidence of other chronic liver diseases. Ethanol intake levels of 20 g daily (or 140 g weekly) are endorsed as the acceptable threshold to define nonalcoholic patients. Liver biopsy is the current gold standard for the diagnosis of NASH and provides prognostic information. Histopathological diagnosis of NASH is based on the following 3 features: (1) hepatic macrovesicular steatosis; (2) lobular inflammation; and (3) ballooning degeneration of hepatocytes. It is impractical to biopsy every patient with suspected NAFLD. Although highly accurate and affordable noninvasive screening tools can differentiate NASH from NAFLD, no imaging studies or laboratory tests are able to precisely diagnose NASH. There is no universal agreement regarding the indications for liver biopsy in NAFLD patients. In Japan, liver biopsies are considered in patients with suspected NAFLD based on several criteria including low platelet counts, elevated fibrosis markers, increasing age and other deciding parameters. Further studies are needed to establish a suitable scoring system that can distinguish steatohepatitis from simple steatosis.