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Encephalopathy literally means disease of the brain. In medical jargon it can refer to a wide variety of degenerative brain disorders with very different etiologies, prognoses and implications. For example, prion diseases, all of which cause transmissible spongiform encephalopathies, are nearly always fatal and have an infectious origin, but other encephalopathies are reversible and can be caused by deficiency, toxins, and several other causes.

There are many types of encephalopathy. Some examples include:

• Glycine encephalopathy - A pediatric metabolic disorder
• Hepatic encephalopathy - Arising from advanced cirrhosis of the liver
• Hypoxic encephalopathy - Permanent or transitory encephalopathy arising from severely reduced oxygen delivery to the brain
• Static encephalopathy - Unchanging, or permanent, brain damage
• Uremic encephalopathy - Arising from high levels of toxins normally cleared by the kidneys -- rare where dialysis is readily available
• Wernicke's encephalopathy - Arising from thiamine deficiency, usually in the setting of alcoholism
• Hashimoto's encephalopathy - Arising from an auto-immune disorder
• Hypertensive encephalopathy - Arising from acutely increased blood pressure
• Toxic-Metabolic encephalopathy - A catch-all for brain dysfunction caused by infection, organ failure, or intoxication.
• Transmissible spongiform encephalopathy - A collection of diseases all caused by prions, and characterized by "spongy" brain tissue (riddled with holes), impaired locomotion or coordination, and a high fatality rate. Includes bovine spongiform encephalopathy (mad cow disease), scrapie, and kuru among others.

Encephalopathy alters brain function and/or structure. It may be caused by an infectious agent (bacteria, virus, or prion), metabolic or mitochondrial dysfunction, brain tumor or increased intracranial pressure, prolonged exposure to toxins (including solvents, drugs, alcohol, paints, industrial chemicals, and certain metals), radiation, chronic progressive trauma, poor nutrition, or lack of oxygen or blood flow to the brain. It is also known that concomitant use of lithium with other neuroleptics may, in rare cases, cause encephalopathy.

The hallmark of encephalopathy is an altered mental state. Depending on the type and severity of encephalopathy, common neurological symptoms are progressive loss of memory and cognitive ability, subtle personality changes, inability to concentrate, lethargy, and progressive loss of consciousness. Other neurological symptoms may include myoclonus (involuntary twitching of a muscle or group of muscles), nystagmus (rapid, involuntary eye movement), tremor, muscle atrophy and weakness, dementia, seizures, and loss of ability to swallow or speak.

Blood tests, spinal fluid examination by lumbar puncture, imaging studies, electroencephalograms and similar diagnostic studies may be used to differentiate the various causes of encephalopathy.

Encephalopathy due to acute liver failure is vitally important to define because emergency liver transplantation and/or artificial liver support can save a life. The diagnosis is given by low level of factors of coagulability (V), intense jaundice and brain edema. Electroencephalogram can be useful. Encephalopathy due to chronic liver failure is also easy to recognize and is frequently triggered by protein intake or gastrointestinal bleeding.

Treatment is symptomatic and varies, according to the type and severity of the encephalopathy. Anticonvulsants may be prescribed to reduce or halt any seizures. Changes to diet and nutritional supplements may help some patients. In severe cases, dialysis or organ replacement surgery may be needed.

Treating the underlying cause of the disorder may improve or reverse symptoms. However, in some cases, the encephalopathy may cause permanent structural changes and irreversible damage to the brain. Some encephalopathies can be fatal.

• Adapted from http://www.ninds.nih.gov/disorders/encephalopathy/encephalopathy.htm

The Diagnosis of Stupor and Coma by Plum and Posner ISBN 0195138988 remains one the of best detailed observational references to the condition

• Brain damage