Encephalopathy

Encephalopathy literally means disease of the brain. In medical jargon it can refer to a wide variety of disorders with very different etiologies, prognoses and implications. For example, anoxic encephalopathy commonly refers to permanent brain damage with often severe impairment of consciousness and mental abilities caused by cessation of oxygen delivery to the brain. In contrast, toxic-metabolic encephalopathy, which has protean causes, is generally completely reversible given reversal of the underlying toxic (infectious) or metabolic insult. Because the word encephalopathy is used in so many contexts, it has no direct synonyms. Contrast to dementia which refers to a permanent reduction in mental abilities from a previously higher level (c.f. mental retardation), always in the absence of acute illness or alteration of consciousness. Also contrast to delirium which refers to an acute confusional state, frequently, but not always, in the setting of acute illness. Because toxic-metabolic encephalopathy is frequently a confusional state in the setting of illness, and delirium is a confusional state, often, but not always, in the setting of illness, the two intergrade seamlessly into each other.

A descriptive example may clarify the distinctions between these entities. An elderly person with Alzheimer's disease, manifested by mild dementia (forgetfulness and impaired judgment) develops pneumonia, a severe infection. They then manifest depressed consciousness, myclonic jerks, jactitation (restless tossing in bed, picking at things), and Cheyne-Stokes respirations (rhythmic increase and decrease in respiratory frequency and depth). These are symptoms (not exclusively) of toxic-metabolic encephalopathy. Because of the severity of their illness they are admitted to the intensive care unit, intubated with an endotracheal tube, mechanically ventilated, and sedated with medications. After a week their infection is cured and they are extubated and breathe independently. At this point they sleep during the day and are awake and agitated at night, have hallucinations, have alternating periods of lucidity and confusion, and manifest paranoia. This is delirium, arising from multiple previous insults (reduced baseline mental faculties, infection, psychoactive medications, altered environment, etc.). With cessation of psychoactive medications, enforcement of normal day/night dark/light cycles, and frequent, gentle, re-orientation to their surroundings, their confusion clears, leaving them mentally with their previous baseline dementia.