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Hepatitis means "inflammation of the liver." It is a disorder in which viruses or other mechanisms produce inflammation in liver cells, resulting in their injury or destruction. The liver is the largest internal organ in the body, occupying the entire upper right quadrant of the abdomen. It performs over 500 vital functions. Some key roles are:
Damage to the liver can impair these and many other processes. Hepatitis varies in severity from a self-limited condition with total recovery to a life-threatening or life-long disease. It can occur from many different causes:
All hepatitis viruses can cause an acute (short term) form of liver disease. Some specific hepatitis viruses (B, C, and D), and some non-viral forms of hepatitis, can cause chronic (long term) liver disease. (Hepatitis A and E viruses do not cause chronic disease.) In some cases, acute hepatitis develops into a chronic condition, but chronic hepatitis can also occur on its own. Although chronic hepatitis is generally the more serious condition, patients with either condition can have varying degrees of severity.
Acute Hepatitis. Acute hepatitis can begin suddenly or gradually, but it has a limited course and rarely lasts beyond 1 or 2 months, although it may last up to 6 months. Usually, there is only spotty liver cell damage and evidence of immune system activity. Rarely, acute hepatitis due to hepatitis B can cause severe, even life-threatening, liver damage.
Chronic Hepatitis. If hepatitis does not resolve after 6 months, it is considered chronic. The chronic forms of hepatitis last for prolonged periods. Doctors usually categorize chronic hepatitis by indications of severity:
Most cases of hepatitis are caused by viruses that infect liver cells and begin replicating. They are defined by the letters A through G:
The name of each type of viral hepatitis condition corresponds to the virus that causes it. For example, hepatitis A is caused by hepatitis A virus (HAV), hepatitis B is caused by hepatitis B virus (HBV), and hepatitis C is caused by hepatitis C virus (HCV).
Scientists do not know exactly how these viruses actually cause hepatitis (inflammation in the liver). As the virus reproduces in the liver, several proteins and enzymes, including many that attach to the surface of the viral protein, are also produced. Some of these may be directly responsible for liver damage. Researchers are investigating elevated levels of specific immune factors, including T cell sub-types, which are found in the livers of patients with hepatitis C or B. T cells are important infection fighters in the immune system that can release powerful inflammatory substances (tumor necrosis factor and interferon gamma) that may be involved in the damage associated with hepatitis B and C.
Autoimmune Hepatitis. Autoimmunehepatitis is a very rare form of chronic hepatitis. Like other autoimmune disorders, its exact cause is unknown. Autoimmune hepatitis may develop on its own or may be associated with other autoimmune disorders, such as systemic lupus erythematosus. In autoimmune disorders, a misdirected immune system attacks the body's own cells and organs (in this case the liver.
Alcoholic Hepatitis. About 10 - 35% of heavy drinkers develop alcoholic hepatitis. In the body, alcohol breaks down into various chemicals, some of which are very toxic to the liver. After years of drinking, liver damage can be very severe, leading to cirrhosis. Although heavy drinking itself is the major risk factor for alcoholic hepatitis, genetic factors may play a role in increasing a person's risk for alcoholic hepatitis. Women who abuse alcohol are at higher risk for alcoholic hepatitis and cirrhosis than are men who drink heavily.
Nonalcoholic fatty liver disease (NAFLD) affects 10 - 24% of the population. It covers several conditions, including nonalcoholic steatohepatitis (NASH). NAFLD has features similar to alcoholic hepatitis, particularly a fatty liver, but it occurs in individuals who drink little or no alcohol. Severe obesity and diabetes are the major risk factors for NAFLD as well as complications from NAFLD. NAFLD is usually benign and very slowly progressive. In certain patients, however, it can lead to cirrhosis, liver failure, or liver cancer. [For more information, see In-Depth Report #75: Cirrhosis.]
Drug-Induced Hepatitis. Because the liver plays such a major role in metabolizing drugs, hundreds of medications can cause reactions that are similar to those of acute viral hepatitis. Symptoms can appear anytime after starting drug treatment. In most cases, they disappear when the drug is withdrawn, but in rare circumstances they may progress to serious liver disease. Drugs most noted for liver interactions include halothane, isoniazid, methyldopa, phenytoin, valproic acid, and the sulfonamide drugs. Very high doses of acetaminophen (Tylenol) have been known to cause severe liver damage and even death, particularly when used with alcohol.
Toxin-Induced Hepatitis. Certain types of plant and chemical toxins can cause hepatitis. These include toxins found in poisonous mushrooms, and industrial chemicals such as vinyl chloride.
Metabolic-Disorder Associated Hepatitis. Hereditary metabolic disorders, such as hemochromatosis (accumulation of iron in the body) and Wilsonâ ' s disease (accumulation of copper in the body) can cause liver inflammation and damage.
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