Non-alcoholic fatty liver disease
Elliot Tapper, M.D.
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Overview
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Non-alcoholic fatty liver disease (NAFLD) is fatty inflammation of the liver when this is 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, which is regarded as a major cause of cryptogenic cirrhosis of the liver.[2]
Signs and symptoms
Symptoms and associations
Most patients with NAFLD have no or few symptoms. Infrequently patients may complain of fatigue, malaise and dull right upper quadrant abdominal discomfort. Mild jaundice can rarely be noticed. More commonly it is diagnosed as a result of abnormal liver function tests during routine blood tests. By definition, alcohol consumption of over 20 g/day excludes the condition.[1]
NAFLD is associated with insulin resistance and the metabolic syndrome (obesity, combined hyperlipidemia, diabetes mellitus (type II) and high blood pressure).[2][1]
Secondary causes
NAFLD can also be caused by the following medications (termed secondary NAFLD):
- Amiodarone
- Antiviral drugs (nucleoside analogues)
- Aspirin / NSAIDS
- Corticosteroids
- Methotrexate
- Nifedipine
- Perhexiline
- Tamoxifen
- Tetracycline
- Valproic acid
Diagnosis
Disturbed liver enzymes are common, and liver ultrasound may show steatosis; it may also be used to exclude gallstone problems (cholelithiasis). A biopsy (tissue examination) of the liver is the only widely accepted test which can distinguish NASH from other forms of liver disease, and can be used to assess the severity of the inflammation and resultant fibrosis.[1]
Other tests generally performed are other blood tests (erythrocyte sedimentation rate, glucose, albumin, renal function etc.) As the liver is important in coagulation, some coagulation studies will generally be done, especially the INR (international normalized ratio). To distinguish this disease from viral hepatitis, blood tests (serology) are generally done (hepatitis A, B, C, EBV, CMV and herpes viruses, as well as rubella) to ensure these are not playing a role. Additionally, autoimmune causes are ruled out with serology. TSH is warranted, as hypothyroidism is more prevalent in NASH patients.[3]
Pathophysiology
NAFLD is considered a spectrum of disease activity. This spectrum begins as fatty accumulation in the liver (hepatic steatosis). A fatty liver can remain without disturbing the function of the liver, but by varying mechanisms and possible insults to the liver, may 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.
The exact cause is still unknown. However both obesity and insulin resistance likely play a strong role in this disease process. The exact reasons and mechanisms by which this disease progresses from one entity to the next is a subject of much research and debate. One such debated mechanisim 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 may be potential causes for this "second hit" phenomenon.[1]
Treatment
Trials are presently being conducted to optimise treatment of NASH. No standard treatment has yet emerged as the "gold standard". General recommendations include improving metabolic risk factors and reducing alcohol intake.[1]
A large number of treatments have been studied for NAFLD. While many may improve biochemical markers, such as alanine transaminase levels, most have not been shown to reverse the histological abnormalities or reduce clinical endpoints:[1]
- Weight loss: gradual weight loss, and possibly bariatric surgery, may improve the process in obese patients.
- Insulin sensitisers (metformin and rosiglitazone but more markedly pioglitazone) have shown efficacy in some studies.
- Antioxidants and ursodeoxycholic acid, as well as lipid-lowering drugs, have little benefit.
History
NASH was described in 1980 in a series of patients of the Mayo Clinic[4]. Its relevance and high prevalence were recognized mainly in the 1990s.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Adams LA, Angulo P. Treatment of non-alcoholic fatty liver disease. Postgrad Med J 2006;82:315-22. PMID 16679470.
- ↑ 2.0 2.1 Clark JM, Diehl AM. Nonalcoholic fatty liver disease: an underrecognized cause of cryptogenic cirrhosis. JAMA 2003;289:3000-4. PMID 12799409.
- ↑ Liangpunsakul S, Chalasani N. Is hypothyroidism a risk factor for non-alcoholic steatohepatitis? J Clin Gastroenterol 2003;37:340-3. PMID 14506393
- ↑ Ludwig J, Viggiano TR, McGill DB, Oh BJ. Nonalcoholic steatohepatitis: Mayo Clinic experiences with a hitherto unnamed disease. Mayo Clin Proc. 1980;55:434-438. PMID 7382552.
External links
- Medscape article on NASH.
- MEDICINENET article on Steatosis.
- NIH page on Nonalcoholic Steatohepatitis