Hepatitis 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 organ in the body, occupying the entire upper right quadrant of the abdomen. It performs over 500 vital functions including:
- The liver processes all of the nutrients the body requires, including proteins, glucose, vitamins, and fats.
- The liver manufactures bile, the greenish fluid stored in the gallbladder that helps digest fats.
- One of the liver's major contributions is to render harmless potentially toxic substances, including alcohol, ammonia, nicotine, drugs, and harmful by-products of digestion.
- Old red blood cells are removed from the blood by the liver and spleen, and the iron contained in them is recycled to the bone marrow to make new red blood cells.
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:
- In the most common hepatitis cases (viral hepatitis), specific viruses incite the immune system to fight off infections. Specific immune factors become over-produced that cause injury.
- Hepatitis can also result from an autoimmune condition, in which abnormal immune factors attack the body's own liver cells.
- Inflammation of the liver can also occur from medical problems, drugs, alcoholism, chemicals, and environmental toxins.
No matter what the cause of hepatitis, it can take either an acute (short term) or chronic (long term) form. 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 having either condition can experience 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. Usually, there is only spotty liver cell damage and evidence of immune system activity, but on rare occasions, acute hepatitis can cause severe, even life-threatening, liver damage.
Chronic Hepatitis. The chronic forms of hepatitis persist for prolonged periods. Experts usually categorize chronic hepatitis by indications of severity:
- Chronic persistent hepatitis is usually mild and nonprogressive or slowly progressive, causing limited damage to the liver.
- Chronic active hepatitis involves extensive liver damage and cell injury beyond the portal tract.
Click the icon to see an image of aggressive hepatitis.
Viral Hepatitis
Most cases of hepatitis are caused by viruses that infect liver cells and begin replicating. They are defined by the letters A through G:
- Hepatitis A, B, and C are the most common viral forms of hepatitis. Investigators are still looking for additional viruses that may be implicated in hepatitis unexplained by the current known viruses.
- Other hepatitis viruses include hepatitis E and hepatitis G. Like hepatitis A, hepatitis E is caused by contact with contaminated food or water. It is not serious except in pregnant women, when it can be life threatening. Hepatitis G is always chronic and most likely has the same modes of transmission as hepatitis C. It does not appear to have serious effects.
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 in the liver of hepatitis C and B patients. T cells are important infection fighters in the immune system that in some cases release powerful inflammatory substances (tumor necrosis factor and interferon gamma) that can cause considerable damage leading to hepatitis B or C.
Autoimmune Chronic Hepatitis
Autoimmune chronic hepatitis accounts for about 20% of all chronic hepatitis cases. Like other autoimmune disorders, this condition develops because a genetically defective immune system attacks the body's own cells and organs (in this case the liver) after being triggered by an environmental factor, probably a virus. Suspects include the measles virus, a hepatitis virus, or the Epstein-Barr virus, which causes mononucleosis. It is also possible that a reaction to a drug or other toxin that affects the liver also triggers an autoimmune response in susceptible individuals. In about 30% of cases, autoimmune hepatitis is associated with other disorders that involve autoimmune attacks on other parts of the body.
Hepatitis Caused by Alcohol and Drugs
Alcohol. 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 in about 10 - 20% of cases. 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. High-fat diets may also increase the risk in heavy drinkers.
Drugs. 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 anywhere from 2 weeks to 6 months 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.
Nonalcoholic Fatty Liver Disease (NAFLD)
Nonalcoholic fatty liver disease (NAFLD) affects between 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.]
