Importance: Nonalcoholic steatohepatitis (NASH) is the inflammatory subtype of nonalcoholic fatty liver disease (NAFLD) and is associated with disease progression, development of cirrhosis, and need for liver transplant. Despite its importance, NASH is underrecognized in clinical practice.

Observations: NASH affects an estimated 3% to 6% of the US population and the prevalence is increasing. NASH is strongly associated with obesity, dyslipidemia, type 2 diabetes, and metabolic syndrome. Although a number of noninvasive tests and scoring systems exist to characterize NAFLD and NASH, liver biopsy is the only accepted method for diagnosis of NASH. Currently, no NASH-specific therapies are approved by the US Food and Drug Administration. Lifestyle modification is the mainstay of treatment, including dietary changes and exercise, with the primary goal being weight loss. Substantial improvement in histologic outcomes, including fibrosis, is directly correlated with increasing weight loss. In some cases, bariatric surgery may be indicated to achieve and maintain the necessary degree of weight loss required for therapeutic effect. An estimated 20% of patients with NASH will develop cirrhosis, and NASH is predicted to become the leading indication for liver transplants in the US. The mortality rate among patients with NASH is substantially higher than the general population or patients without this inflammatory subtype of NAFLD, with annual all-cause mortality rate of 25.56 per 1000 person-years and a liver-specific mortality rate of 11.77 per 1000 person-years.

Conclusions and relevance: Nonalcoholic steatohepatitis affects 3% to 6% of the US population, is more prevalent in patients with metabolic disease and obesity, progresses to cirrhosis in approximately 20% of cases, and is associated with increased rates of liver-specific and overall mortality. Early identification and targeted treatment of patients with nonalcoholic steatohepatitis are needed to improve patient outcomes, including directing patients toward intensive lifestyle modification to promote weight loss and referral for bariatric surgery as indicated for management of obesity and metabolic disease.