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Abnormal brain function may occur because of many different conditions; for example, lack of nutrients, poisoning, infection, structural changes, or anoxia (lack of oxygen delivery to the brain).
Alcohol is a classic example of an acute and chronic ingestion that causes brain function changes. When a person drinks alcohol to excess, it alters brain activity. An acutely intoxicated person demonstrates lack of judgment and decreased reflexes and coordination. If enough alcohol is ingested, the parts of the brain that control wakefulness and breathing can be depressed to the point that the person can become comatose. These effects are short lived and transient as the liver metabolizes the alcohol and removes it from the body. When the alcohol is gone, the individual returns to normal functioning. However, when alcohol is repeatedly abused, it can cause liver disease increasing ammonia levels and encephalopathy or there can be direct damage to the brain with loss of brain tissue.
Wernicke-Korsakoff syndrome is one type of alcoholic encephalopathy that is caused by thiamine (vitamin B1) deficiency due to malnutrition. The malnutrition occurs because most of the dietary calories are derived from alcohol, decreased appetite from a regular diet, and possibly malabsorption of nutrients from the intestine. There may be memory loss and confusion, loss of coordination and ataxia with a wobbling gait (walk), and confusion.
Non-alcohol related causes can include AIDS, cancer, renal (kidney) dialysis, and hyperthyroidism (thyrotoxicosis).
Anoxic (an= no + oxia= oxygen) or hypoxic (hypo=less + oxia=oxygen) encephalopathy is a condition where brain tissue is deprived of oxygen and there is global loss of brain function. The longer brain cells lack oxygen, the more damage occurs.
In pregnancy, the fetus may develop hypoxic encephalopathy if blood supply from the placenta is compromised. Placenta abruptio and placenta previa are two situations that occur in the third trimester leading to fetal distress. Difficulties during the delivery, for example when the umbilical cord is wrapped around the fetus' neck, may cause distress and compromise oxygen delivery to its brain.
Anoxic or hypoxic encephalopathy may occur at any time in life. In cardiac arrest, the heart stops and oxygen isn't pumped to the brain. The purpose of starting CPR (cardiopulmonary resuscitation) immediately is to try to continue blood flow and oxygen delivery. Delays in this process may result in brain cell damage and death.
Hypertensive encephalopathy occurs when blood pressure rises to levels high enough to affect brain function. Headache, nausea and vomiting, changes in vision, and decreased level of consciousness may be due to markedly elevated pressure. This condition is also known as a hypertensive crisis (hypertensive emergency), where high blood pressure readings are associated with organ failure. In addition to encephalopathy, there can also be symptoms of chest pain, shortness of breath, and kidney failure. Hypotension (low blood pressure) due to many factors (for example, bleeding, major infection, or blood pressure medications) may result in encephalopathy with symptoms of fainting, weakness, and altered mental status.
Infections are a cause of encephalopathy. Many types of bacteria, viruses, and fungi can cause encephalitis by infection and inflammation of the brain tissue or of the meninges (meningitis) that line the brain and spinal cord.
Prions are the cause of rare infections like Jacob-Creutzfeldt disease, which is related to bovine spongiform encephalopathy (BSE) or mad cow disease. The prions invade brain tissue and begin to form abnormal protein deposits between brain cells, disrupting tissue structure. The disease is progressive and untreatable leading ultimately to death. Kuru is another type of human prion brain infection.
Ischemic encephalopathy occurs because the small blood vessels that supply blood to brain tissue gradually narrow and cause a generalized decrease in blood flow to the brain. This causes progressive loss of brain tissue with associated loss of function. Risk factors for narrowing blood vessels in the brain are the same as for heart disease and peripheral vascular disease and include smoking, high blood pressure, high cholesterol, and diabetes.
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