Introduction

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:

• 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.

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 that cause injury become overproduced.
• 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.

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:

• 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.

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: