Encephalopathy /ɛnˌsɛfəˈlɒpəθi/ means disorder or disease of the brain.  In modern usage, encephalopathy does not refer to a single disease, but rather to a syndrome of overall brain dysfunction; this syndrome can have many different organic and inorganic causes.
Encephalopathy is a difficult term because it can be used to denote either a disease or finding (i.e., an observable sign in a patient).
When referring to a finding, encephalopathy refers to permanent (or degenerative)  brain injury, or a reversible one. It can be due to direct injury to the brain, or illness remote from the brain. The individual findings that cause a clinician to refer to a patient as having encephalopathy include intellectual disability, irritability, agitation, delirium, confusion, somnolence, stupor, coma and psychosis. As such, describing a patient as having a clinical picture of encephalopathy is not a very specific description.
When referring to a disease, encephalopathy refers 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 have a number of causes including nutritional deficiencies and toxins.
Signs and 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 involuntary grasping and sucking motions, myoclonus (involuntary twitching of a muscle or group of muscles), asterixis ("flapping tremor" of the hand when wrist is extended), 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.
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.
- Chronic traumatic encephalopathy: Progressive degenerative disease associated with multiple concussions and other forms of brain injury.
- Lyme encephalopathy: Arising from Lyme disease bacteria, including Borrelia burgdorferi .
- 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 100% mortality 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.
- Salmonella encephalopathy: A form of encephalopathy caused by food poisoning (especially out of peanuts and rotten meat) often resulting in permanent brain damage and nervous system disorders.
- Encephalomyopathy: A combination of encephalopathy and myopathy. Causes may include mitochondrial disease (particularly MELAS) or chronic hypophosphatemia, as may occur in cystinosis.
Blood tests, cerebrospinal fluid examination by lumbar puncture (also known as spinal tap), brain imaging studies, EEG, 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.
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.
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. These permanent deficits can be considered a form of stable dementia. Some encephalopathies can be fatal.