Doctor's Notes on Encephalopathy
The term “encephalopathy” is used to refer to an abnormality of brain function or structure. There are many conditions that can cause encephalopathy. Examples of causes include lack of nutrients, lack of oxygen delivery to the brain via the bloodstream, poisoning, alcoholism, infection, kidney failure, liver failure, trauma, or anatomic abnormalities. Some forms of encephalopathy may be reversible while others are permanent.
Signs and symptoms of encephalopathy can vary widely according to the cause and the severity of the underlying condition. Symptoms range from mild lethargy to coma. Associated symptoms can include memory loss, confusion, poor judgment, psychosis, cognitive impairment, and hallucinations. In cases of profound encephalopathy, even basic brain functions that control wakefulness, breathing, heartbeat, and temperature are affected.
Encephalopathy describes abnormal brain function due to problems with the brain tissue. Symptoms of encephalopathy can be generalized causing decreased level of consciousness from minimal lethargy to coma. Encephalopathy can cause abnormal thought processes including confusion, poor memory, hallucinations, and even psychotic thinking.
The symptoms may be evident because the parts of the body that the brain controls may not work appropriately. There may be incoordination and difficulty walking (ataxia) or there may be abnormalities with vision and eye movement. The encephalopathy may mimic stroke with weakness and numbness of one side of the body, including facial droop and speech problems. The abnormalities may not only affect motor function but also sensation. It all depends upon what part of the brain is not functioning.
In some patients, the encephalopathy is so profound that it affects basic brain functions that control wakefulness, breathing, heartbeat, and temperature.
The symptoms depend on the basic cause of encephalopathy and the potential for reversal of the cause. Symptoms may be present and remain constant or they may wax and wane. The symptoms may present once and never recur or they can be progressive and lead to death. For example, low blood glucose (hypoglycemia) may be easily reversed with no brain damage, while profound anoxia may be partially reversible or result in disability or death.
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.
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.
Metabolic encephalopathy (toxic metabolic encephalopathy) is a broad category that describes abnormalities of the water, electrolytes, vitamins, and other chemicals that adversely affect brain function. In addition to liver and kidney waste products, it may include abnormally high or low blood sugar (hyperglycemia, hypoglycemia), thyroid problems, and sodium levels in the blood (hyponatremia=low sodium, hypernatremia=high sodium).
Toxic metabolic encephalopathy can also include medication side effects or drug ingestions affecting the chemical transmitters in the brain. Called neurotransmitters, dopamine, GABA, serotonin, acetylcholine, and glutamine help nerve endings pass electrical signals between brain cells. Alterations in these transmitters can decrease brain function. Concentrations of neurotransmitters and abnormal function can be seen in seizure disorders and Alzheimer's disease.
Head trauma can cause brain damage due to bleeding in and around the brain. This can cause increased pressure within the skull that presses on brain tissue and cause abnormal brain function. Shear injuries to brain tissue can disrupt the neurons that connect brain cells together. Aside from the direct brain tissue injury, increased pressure buildup within the skull can decrease the amount of blood flow to the brain causing anoxic or hypoxic damage.
Blood supply to the brain may be compromised because of stroke, where one of the arteries to the brain becomes blocked and that part of the brain is replaced with scar tissue. If enough cells are injured, there can be permanent damage. Alternatively, hemorrhagic stroke occurs when bleeding occurs into the brain itself causing damage.
Chronic Traumatic Encephalopathy (CTE) describes a brain that has gradual degeneration in function because of repeated head injuries causing both concussions with symptoms and those that are asymptomatic. The symptoms of concussion usually fade, but months or years later, new symptoms can occur. CTE symptoms gradually progress. Initially, there may be concentration and memory issues with episodes of disorientation and confusion, dizziness, and headache. Emotions can be labile and the patient can develop aggressive and psychotic behavior. As CTE progresses, the behavior can become erratic and Parkinson's-like symptoms may be seen. Finally, thought processes decrease even further into dementia with more Parkinson's symptoms including speech and walking abnormalities. These symptoms are progressive and cannot be stopped.
The diagnosis of CTE is made clinically. Neither bleeding nor major abnormalities are seen on CT scan and it appears to act like other diseases that attack brain function. It can be confirmed in retrospect on autopsy and dissection of the brain. An abnormal protein called tau builds up in the brain and causes abnormal nerve fiber and cell tangles in the brain. At autopsy, the brain has a different appearance than that seen in Alzheimer's disease.
Acute or chronic kidney failure can lead to uremic encephalopathy. When the kidneys fail to adequately cleanse the bloodstream, a variety of toxins can gradually build and cause brain function to decrease. If kidney function is not restored or if dialysis is not instituted, permanent brain tissue damage can occur, ultimately leading to death.
Although the brain is protected by tough bone (skull) and padding (membranes), it can still be injured. Head injuries that are severe enough to affect brain function are termed traumatic brain injuries (TBIs). Damage can range from mild to severe as the brain can affect everything you do.
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Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.