Fat accumulates in the liver. Liver function is affected and liver failure can ensue. How is it defined? Patients with nonalcoholic fatty liver disease (NAFLD) have hepatic steatosis, with or without inflammation and fibrosis. In addition, no secondary causes of hepatic steatosis are present. If there is inflammation then it is called nonalcoholic steatohepatitis (NASH) and if there is no inflammation then it is called NAFLD. Worldwide, NAFLD has a reported prevalence of 6 to 35 percent (median 20 percent). Who is likely to get it? Those with central obesity, those with type 2 diabetes, dyslipidemia, and metabolic syndrome also it tends to occur in men and the elderly. So keep an eye out.
Is it increasing? Yes and here are some figures from the USA.
Between 1988 and 1994, the prevalence of NAFLD was 5.5 percent, between 1999 and 2004 it was 9.8 percent, and between 2005 and 2008 it was 11 percent, accounting for 47, 63, and 75 percent of chronic liver disease during those time periods, respectively
In the United States, studies report a prevalence of NAFLD of 10 to 46 percent, with most biopsy-based studies reporting a prevalence of NASH of 3 to 5 percent . Worldwide. NAFLD has a reported prevalence of 6 to 35 percent (median 20 percent). In a prospective study of 400 US military personnel and their families (mean age 55 years), the prevalence of NAFLD by ultrasound was 46 percent.
Why does the liver accumulate fat and why does this lead to inflammatory and necrotic changes? It is not currently well understood. The most widely supported theory implicates insulin resistance as the key mechanism leading to hepatic steatosis, and perhaps also to steatohepatitis. Others have proposed that a “second hit”, or additional oxidative injury, is required to manifest the necroinflammatory component of steatohepatitis. Hepatic iron, leptin, antioxidant deficiencies, and intestinal bacteria have all been suggested as potential oxidative stressors.
How are you going to pick up NAFLD? Patients who are investigated usually tend to have a large liver on an average 18 cm in span (12 to 21 cm span depending on height). There may be stigmata of chronic liver disease such as palmar erythema, spider angiomata, ascites. Patients with NAFLD may have mild or moderate elevations in the aspartate aminotransferase (AST) and alanine aminotransferase (ALT) . When elevated, the AST and ALT are typically two to five times the upper limit of normal, with an AST to ALT ratio of less than one (unlike alcoholic fatty liver disease, which typically has a ratio greater than two). It is not possible to predict the degree of inflammation from the rise of these enzymes or even the lack of rise of the enzymes. A liver biopsy is not always indicated as ultrasound imaging may be sufficient to make the diagnosis provided there is no history of alcoholism, viral hepatitis or other causes of liver disease. A biopsy may be done to see the degree of steatohepatitis or if the diagnosis is in doubt. Vibration controlled transient elastography, which is routinely used to grade fibrosis based on liver stiffness, is also being developed to grade hepatic steatosis.
If the fat is being deposited in the liver is it harming other parts of the body? The two most clinically significant diseases likely to be associated with NAFLD are acute myocardial infarction or a stroke.
What research is being done on this? “Non-alcoholic fatty liver disease and risk of incident acute myocardial infarction and stroke: findings from matched cohort study of 18 million European adults” was published on 8th October 2019. The objective was to estimate the risk of acute myocardial infarction (AMI) or stroke in adults with non-alcoholic fatty liver disease (NAFLD) or non-alcoholic steatohepatitis (NASH). It was a large study with 120,795 adults participating in it. So what did the study find? The conclusion was that the diagnosis of NAFLD in current routine care of 17.7 million patient appears not to be associated with AMI or stroke risk after adjustment for established cardiovascular risk factors. Cardiovascular risk assessment in adults with a diagnosis of NAFLD is important but should be done in the same way as for the general population.
This information is taken from the BMJ and other sources.
The reference is:
BMJ 2019; 367 doi: https://doi.org/10.1136/bmj.l5367 (Published 08 October 2019)
Cite this as: BMJ 2019;367:l5367