Encephalopathy is a medical term used to describe any type of brain disease that alters brain function or structure. It has many causes, including infection with bacteria, viruses or a type of protein called a prion that is altered from its natural form. Infection with HIV can cause encephalopathy in some patients.

Encephalopathy can lead to serious complications that affect whole body systems. The complications include swelling of the brain (cerebral edema), irreversible neurological impairment and increased risk of certain medical conditions (e.g., respiratory failure, cardiovascular collapse, kidney failure). In some cases, patients may lapse into a coma that ends in death.

The forms of encephalopathy include:

• Hepatic encephalopathy. Occurs when the liver stops functioning properly and fails to metabolize or detoxify substances in the body. This allows toxic substances such as ammonia to build up in the bloodstream and to damage the central nervous system. There are many potential causes of hepatic encephalopathy, including infection and liver diseases such as cirrhosis.
  
  
• Transmissible spongiform encephalopathies (TSEs). These rare and deadly degenerative brain disorders are marked by tiny holes that make the brain appear “spongy.” They occur as a result of an abnormal version of a protein called a prion. Creutzfeldt-Jakob disease (CJD) is the best-known of the human TSEs. A newly recognized form is called variant Creutzfeldt-Jakob disease (vCJD). This is believed to result from consumption of beef contaminated with bovine spongiform encephalopathy (BSE), also known as mad cow disease. Other TSEs include kuru and Gerstmann Straussler Scheinker disease. People sometimes become infected with TSEs through contact with infected tissue, transplants (e.g., cornea), body fluids or contaminated medical instruments.