The liver functions by clearing the body of drugs toxins and poisons and metabolizing nutrients for use. When the liver is damaged in the short or long term due to infection or other causes there may be liver disease.

Classification of liver disease based on causes

To divide causes of liver disease based on the basic pathology we can classify them as drug or toxin induced; infective; and metabolic or other causes (1, 2, 3) : –

1. Drug or toxin induced –
   1. Alcohol related liver disease – Those who take too much alcohol over long periods of time risk the health of their liver. Initially the liver cells swell up and there may be fat deposits. The condition is called alcoholic fatty liver. Thereafter the liver as a whole is inflammed and swollen, which gives rise to alcoholic hepatitis. Finally there is scarring leading to liver cirrhosis. The liver loses its ability to function and may fail which can be fatal.
   2. Drug induced liver damage – Some medicines may also damage the liver. These may range from common drugs like acetaminophen (fever remedy) that may lead to liver failure in overdoses. Some drugs that lower cholesterol like Statins and Niacin also damage the liver. Other liver damaging drugs include nitrofurantoin, tetracycline, isoniazid (antibiotics) or Methotrexate (anti-cancer drug). Some herbal drugs also damage the liver. These include kava kava, ma huang etc. Many mushrooms can also cause severe liver damage.
2. Infective -
   1. Hepatitis A virus – This virus is transmitted via faeces and contaminated water. Although it leads to an acute liver damage, in some individuals it may lead to long term liver disease. Acute liver damage may manifest as jaundice, fever, nausea and vomiting. Although mild, this condition may lead to severe damage and even liver failure.
   2. Hepatitis B and C virus are spread via infected blood transfusion, contaminated needles and other body fluids. Long term infection with these viruses may even lead to liver cancer. There is a vaccine against hepatitis B but none against hepatitis C.
3. Metabolic or other causes
   1. Non alcoholic fatty liver disease – occurs in individuals who do not consume, or drink little, alcohol. They develop fatty deposits over the liver. They occur commonly in people that are obese, diabetic, and have high blood cholesterol.
   2. Hemochromatosis – Liver is the storehouse for iron. Hemochromatosis can occur when there is too much iron deposited in the liver. This is usually a genetic condition. This may lead to cirrhosis and liver failure in some. This is one of the commonest inherited disorders in northern Europe affecting one in 300 people.
   3. Wilson’s disease – This condition results from too much deposit of copper in the liver. Normally the liver controls the amount of copper in the body. In Wilson’s disease this is disturbed. This is also an inherited condition that affects children and leads to liver cirrhosis and even failure.
   4. Autoimmune hepatitis - This occurs when the body’s immune system perceives the liver cells as foreign and attack it. This commonly affects women more than men.
   5. Primary biliary cirrhosis – this is also a condition that is thought to be of autoimmune pathology. There is severe cirrhosis that destroys the bile ducts that allow normal flow of bile thorough liver.
   6. Primary sclerosing cholangitis – There is severe inflammation of bile ducts that makes them scarred and narrow and prevents the flow of bile. This leads to pain, fever and jaundice and formation of bile stones.
   7. Obstetric cholestasis – This occurs during pregnancy. There is severe obstruction to bile flow that can pose a risk to the unborn baby. It affects 1 in 40 pregnancies in UK.
   8. Gall bladder stones – One in 10 people in UK may develop stones in their gall bladder. This is common among middle aged females who are overweight.
   9. Liver cancer – Liver cancer may be primary, where it begins in the liver, or secondary, where it begins elsewhere. Secondary liver cancer may be a metastatic or advanced form of another cancer like breast, lung, bone etc. that has travelled to affect the liver. Primary liver cancer risk rises in people with liver cirrhosis.

Further Reading

What is liver disease?
Liver disease symptoms 
Liver disease diagnosis
Liver disease treatments