Delirium and psychotic symptoms--an integrative model.
Delirium may be a common cause of psychotic symptoms such as hallucinations, bizarre delusions and thought-disorder, even in conditions such as schizophrenia, mania and depression, where delirium has traditionally been excluded by definition. This situation is a consequence of the insensitivity of current clinical criteria for the diagnosis of delirium, which recognize only the most severe forms of functional brain impairment (including disorientation and clouding of consciousness). Serial electroencephalograms (EEGs) are the most sensitive method for detecting delirium, and until such studies are performed, the true incidence of delirium in psychotic patients will not be known. The suggested causal mechanism of delirium in psychosis is sleep disruption. Sleep is essential for maintenance of memory circuits, which otherwise suffer progressive synaptic weakening due to molecular turnover. When sleep is disrupted, memory circuits deteriorate, and subsequent activation of incompetent circuits can generate psychotic symptoms. Induction of physiologically normal sleep would therefore be expected to produce significant clinical improvement in patients with psychotic symptoms. Furthermore, the 'anti-delirium' action of electroconvulsive therapy may account for its effectiveness in alleviating a wide range of psychiatric and neurological pathologies.