This chapter covers the initial evaluation and management of a psychotic emergency department patient with particular emphasis on the process of separating psychiatric causes from medical causes of psychosis. Hallucinations, delusions, thought disorganization, agitation, and catatonia are the most common features of psychosis. Emergency physicians have a primary responsibility to determine which category, organic or functional, defines a patient's psychotic episode. Substance-induced toxicity is a more common cause of acute delirium in children, and should be considered early in the evaluation. Dementia (particularly vascular dementia and Alzheimer's disease) predisposes patients to psychosis that may require inpatient psychiatric management. The etiology of postpartum psychosis is unknown but familial susceptibility suggests a genetic link, and rapid hormone changes seem to play a triggering role. The chapter discusses the management of agitation, and provides information on the medical screening examination, which allows for ultimate categorization of psychosis and appropriate disposition.

The biological approach to functional psychosis began to gain ground and went on to become the dominant explanatory paradigm. In schizophrenia, studies of memory now rival, and may even have overtaken, the other main area of neuropsychological investigation, frontal or executive function. In affective psychosis, the long-standing observation that memory may be affected in depression has gone from being automatically considered secondary to motivational or other factors, to a phenomenon deserving recognition and investigation in its own right. Both schizophrenia and manic-depressive psychosis are associated with memory deficits as part of a wider pattern of cognitive impairments, which can occasionally become severe. The features of the impairment in both disorders, plus other circumstantial evidence, suggest that it is 'biological' in nature, but not 'neurological', that is, that it has different underlying causes than those normally encountered in neurology.