Non-alcoholic fatty liver disease

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Non-alcoholic fatty liver disease
Classification and external resources

Micrograph of non-alcoholic fatty liver disease, demonstrating marked macrovesicular steatosis. Trichrome stain
ICD-10K76.0
ICD-9571.8
DiseasesDB29786
eMedicinemed/775
 
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Non-alcoholic fatty liver disease
Classification and external resources

Micrograph of non-alcoholic fatty liver disease, demonstrating marked macrovesicular steatosis. Trichrome stain
ICD-10K76.0
ICD-9571.8
DiseasesDB29786
eMedicinemed/775

Non-alcoholic fatty liver disease (NAFLD) is one cause of a fatty liver, occurring when fat is deposited (steatosis) in the liver not due to excessive alcohol use. It is related to insulin resistance and the metabolic syndrome and may respond to treatments originally developed for other insulin-resistant states (e.g. diabetes mellitus type 2) such as weight loss, metformin and thiazolidinediones.[1] Non-alcoholic steatohepatitis (NASH) is the most extreme form of NAFLD, and is regarded as a major cause of cirrhosis of the liver of unknown cause.[2]

Contents

Signs and symptoms

Most patients with NAFLD have few or no symptoms. Patients may complain of fatigue, malaise, and dull right-upper-quadrant abdominal discomfort. Mild jaundice may be noticed although this is rare. More commonly NAFLD is diagnosed following abnormal liver function tests during routine blood tests. By definition, alcohol consumption of over 20 g/day (about 25 ml/day) excludes the condition.[1]

NAFLD is associated with insulin resistance and metabolic syndrome (obesity, combined hyperlipidemia, diabetes mellitus (type II) and high blood pressure).[1][2]

Causes

NAFLD can also be caused by some medications:[1]

Soft drinks

Soft drinks have been linked to NAFLD through the presence of high fructose corn syrup which may cause increased deposition of fat in the abdomen[3] though the consumption of fructose may be no worse than the consumption of any other sugar.[4]

Genetics

Indian men have a high prevalence of non-alcoholic fatty liver disease. Two genetic mutations for this susceptibility have been identified, and these mutations provided clues to the mechanism of NASH and related diseases.

Polymorphisms (genetic variations) in the single-nucleotide polymorphisms (SNPs) T455C and C482T in APOC3 are associated with fatty liver disease, insulin resistance, and possibly hypertriglyceridemia. 95 healthy Asian Indian men and 163 healthy non-Asian Indian men around New Haven, Connecticut were genotyped for polymorphisms in those SNPs. 20% homogeneous wild both loci. Carriers of T-455C, C-482T, or both (not additive) had a 30% increase in fasting plasma apolipoprotein C3, 60% increase in fasting plasma triglyceride and retinal fatty acid ester, and 46% reduction in plasma triglyceride clearance. Prevalence of non-alcoholic fatty liver disease was 38% in carriers, 0% wild (normal). Subjects with fatty liver disease had marked insulin resistance.[5]

Pathophysiology

NAFLD is considered to cover a spectrum of disease activity. This spectrum begins as fatty accumulation in the liver (hepatic steatosis). A liver can remain fatty without disturbing liver function, but by varying mechanisms and possible insults to the liver may also progress to outright inflammation of the liver. When inflammation occurs in this setting, the condition is then called NASH. Over time, up to 20 percent of patients with NASH may develop cirrhosis.[citation needed] Cigarette smoking is not associated with an increased risk of developing NASH.

The exact cause of NAFLD is still unknown. However, both obesity and insulin resistance probably play a strong role in the disease process. The exact reasons and mechanisms by which the disease progresses from one stage to the next are not known.

One debated mechanism proposes a "second hit", or further injury, enough to cause change that leads from hepatic steatosis to hepatic inflammation. Oxidative stress, hormonal imbalances, and mitochondrial abnormalities are potential causes for this "second hit" phenomenon.[1]

Diagnosis

Common findings are elevated liver enzymes and a liver ultrasound showing steatosis. An ultrasound may also be used to exclude gallstone problems (cholelithiasis). A liver biopsy (tissue examination) is the only test widely accepted as definitively distinguishing NASH from other forms of liver disease and can be used to assess the severity of the inflammation and resultant fibrosis.[1]

Non-invasive diagnostic tests have been developed, such as FibroTest, that estimates liver fibrosis,[6] and SteatoTest, that estimates steatosis,[7] however their use has not been widely adopted.[8] Apoptosis has been shown to be the mechanism of hepatocyte destruction and caspase-cleaved cytokeratin 18 (M30-Apoptosense ELISA) in serum/plasma is often elevated in patients with NASH.[9][10]

Other diagnostic tests are available. Relevant blood tests include erythrocyte sedimentation rate, glucose, albumin, and renal function. Because the liver is important for making proteins used in coagulation some coagulation related studies are often carried out especially the INR (international normalized ratio). Blood tests (serology) are usually used to rule out viral hepatitis (hepatitis A, B, C and herpes viruses like EBV or CMV), rubella, and autoimmune related diseases. Hypothyroidism is more prevalent in NASH patients which would be detected by determining the TSH.[11]

It has been suggested that in cases involving overweight patients whose blood tests do not improve on losing weight and exercising that a further search of other underlying causes be undertaken. This would also apply to those with fatty liver who are very young or not overweight or insulin-resistant. In addition those whose physical appearance indicates the possibility of a congenital syndrome, have a family history of liver disease, have abnormalities in other organs, and those that present with moderate to advanced fibrosis or cirrhosis.[12]

Management

A large number of treatments for NAFLD have been studied. While many appear to improve biochemical markers such as alanine transaminase levels, most have not been shown to reverse histological abnormalities or reduce clinical endpoints:[1]

Epidemiology

The prevalence of non-alcoholic fatty liver disease ranges from 9 to 36.9% of the population in different parts of the world.[22][23][24] Approximately 20% of the United States population suffers from non-alcoholic fatty liver, and the prevalence of this condition is increasing.[25] The prevalence of non-alcoholic fatty liver disease is higher in Hispanics, which can be attributed to high rates of obesity and type 2 diabetes in Hispanic populations.[26] Non-alcoholic fatty liver disease is also more common among men than women in all age groups until age 60, where the prevalence between sex equalize. This is due to the protective nature of estrogen.[27]

In children

Pediatric Nonalcoholic Fatty Liver Disease (NAFLD) was first reported in 1983.[28] It is currently the primary form of liver disease among children.[29] NAFLD has been associated with the metabolic syndrome, which is a cluster of risk factors that contribute to the development of cardiovascular disease and type 2 diabetes mellitus. Studies have demonstrated that abdominal obesity and insulin-resistance in particular are thought to be key contributors to the development of NAFLD.[30][31][32][33][34] Because obesity is becoming an increasingly common problem worldwide, the prevalence of NAFLD has been increasing concurrently.[35] Moreover, boys are more likely to be diagnosed with NAFLD than girls with a ratio of 2:1.[36][37] Studies have suggested that progression toward a more advance stage of disease among children is dependent on age and presence of obesity.[32] This finding is consistent with previous studies in adults demonstrating the same association between age and obesity, and liver fibrosis.[38][39] Early diagnosis of NAFLD in children may help prevent the development of liver disease during adulthood.[32][40] This is challenging as most children with NAFLD are asymptomatic with few showing abdominal pain.[40] Currently, liver biopsy is considered the gold standard for diagnosing NAFLD.[29] However, this method is invasive, costly and bears greater risk for children, and noninvasive screening and diagnosing methods would have significant public health implications for children with NAFLD.[29] The only treatment shown to be truly effective in childhood NAFLD is weight loss.[41][42]

See also

References

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