Delirium has been recognized and described since antiquity. It is a brain disturbance manifested by a syndrome of diverse neuropsychiatric symptoms. Various terms have been used for delirium, such as acute brain disorder, metabolic encephalopathy, organic brain syndrome, and ICU psychosis.
Since its initial description by Kahlbaum (1828-1899) over a century ago, catatonia has been associated with psychiatric, neurologic, and medical disorders. Contemporary authors view catatonia as a syndrome of motor signs in association with disorders of mood, behavior, or thought. Some motor features are classic but infrequent (eg, echopraxia, waxy flexibility) while others are common in psychiatric patients (eg, agitation, withdrawal), becoming significant because of their duration and severity.