Nonalcoholic fatty liver disease (NAFLD) is defined by the presence of hepatic steatosis detected on either imaging or histology in the absence of secondary causes of fatty liver (e.g., excessive alcohol consumption) or other chronic liver diseases.1 For practical NAFLD diagnosis purposes, excessive alcohol intake can be defined as an active or recent history of more than 21 standard drinks per week in men and more than14 standard drinks per week in women. For the sake of terminology, NAFLD is characterized by fatty liver infiltration, affecting at least 5% of hepatocytes, with no evidence of hepatocyte injury, whereas nonalcoholic steatohepatitis (NASH) is defined as the presence of necroinflammation with or without fibrosis in a background of fatty liver.1
NASH and the degree of fibrosis are the two most important determinants of the natural history of NAFLD. NASH can evolve into fibrosis and cirrhosis, whereas advanced fibrosis and cirrhosis (stages 3 or 4 of fibrosis) significantly increase the risk of liver-related decompensation and mortality. NAFLD, per se, has been associated with an increased risk of overall mortality, compared with that of the general population.2 The three most common causes of mortality for patients with NAFLD are cardiovascular diseases (CVD), extrahepatic malignancies, and liver-related deaths. Mortality and liver-related events, including hepatic decompensation and hepatocellular carcinoma (HCC), may significantly increase in a dose-dependent manner with increasing fibrosis stages, and stages 3 or 4 of fibrosis may display the highest rates of all-cause mortality and liver-related events.3,4 It is important to note, however, that almost 15% of HCCs occur in patients with NAFLD who do not have cirrhosis.5 The presence of commonly associated comorbidities such as obesity, insulin resistance or diabetes, dyslipidemia, hypothyroidism, polycystic ovary syndrome, and sleep apnea may contribute to an increased risk of NASH and advanced fibrosis and, therefore, an accelerated clinical course of NAFLD.