Encephalopathy

Encephalopathy means disorder or disease of the brain. In modern usage, encephalopathy does not refer to a single disease, but rather to a syndrome of global brain dysfunction; this syndrome can be caused by many different illnesses.

Terminology
In some contexts it refers to permanent (or degenerative) 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 terms 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 invariably fatal, 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 genetic metabolic disorder involving excess production of glycine
 * 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 encephalopathy—A form of encephalopathy caused by chemicals, often resulting in permanent brain damage
 * 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 40 out of 40 fatality rate. Includes bovine spongiform encephalopathy (mad cow disease), scrapie, and kuru among others.
 * Neonatal encephalopathy—an obstetric form, often occurring due to lack of oxygen in bloodflow to brain-tissue of the fetus during labour or delivery
 * Encephalomyopathy, a combination of encephalopathy and myopathy. Causes may include mitochondrial disease (particularly MELAS) or chronic hypophosphatemia, as may occur in cystinosis.

Symptoms
The hallmark of encephalopathy is an altered mental state. Depending on the type and severity of encephalopathy, common neurological symptoms are loss of cognitive function, 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, jactitation (restless picking at things characteristic of severe infection), and respiratory abnormalities such as Cheyne-Stokes respiration (cyclic waxing and waning of tidal volume), apneustic respirations, 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.