Encephalopathy /?n?s?f??l?p??i/ literally means disease of the brain. In some contexts it refers to permanent brain injury, and in others it is reversible. It can be due to direct injury to the brain, or illness remote from the brain. In medical jargon it can refer to a wide variety of 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 nutritional deficiencies, toxins, and several other causes.

Types

There are many types of encephalopathy. Some examples include:

• Mitochondrial encephalopathy - Metabolic disorder caused by dysfunction of mitochondrial DNA. Can affect many body systems, particularly the brain and nervous system.
• Glycine encephalopathy - A pediatric metabolic disorder
• Hepatic encephalopathy - Arising from advanced cirrhosis of the liver
• Hypoxic ischemic 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
• Lyme encephalopathy - Arising from the Borrelia Burgdorferi bacteria.
• 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.

Causes

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, exposure to toxins (including solvents, excess animal protein, drugs, alcohol, paints, industrial chemicals, and certain metals), radiation, trauma, poor nutrition, or lack of oxygen or blood flow to the brain.

The hallmark of encephalopathy is an altered mental state. Depending on the type and severity of encephalopathy, common neurological symptoms are loss of cognitive ability, subtle personality changes, inability to concentrate, lethargy, and depressed consciousness. Other neurological signs may include myoclonus (involuntary twitching of a muscle or group of muscles), asterixis (abrupt loss of muscle tone, quickly restored), nystagmus (rapid, involuntary eye movement), tremor, seizures, and respiratory abnormalities such as Cheynes-Stokes respiration (cyclic waxing and waning of tidal volume) and post-hypercapnic apnea.

Diagnosis

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.

Diagnosis is frequently clinical. That is, no set of tests give the diagnosis, but the entire presentation of the illness with nonspecific test results informs the experienced clinician of the diagnosis.

Therapy

Treatment 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.

Prognosis

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.

References

• 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

See also

• Brain damage
• Neurobiology
• Neurobiological brain disorder

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