Psychosis is a state in which the individual experiences a severe disconnection from reality. The most common symptoms associated with psychotic disorders are delusions and hallucinations. Delusions are false beliefs about experiences, oneself, or the environment that cannot be altered in the face of contradictory evidence. An example would be delusions of persecution in which the individual believes that others are tormenting, ridiculing, or intending to harm him or her. Hallucinations involve false perceptions in any sensory modality without insight into their pathological nature. The most common hallucination is auditory, which is generally experienced as “hearing voices.” Other symptoms associated with psychotic disorders include negative symptoms such as restricted emotional expression (flat affect), sparse language output (alogia), poor initiation and persistence of goal-directed behaviors (avolition), disorganized thoughts, speech, or behaviors, or a severe decrease in reactivity to one's surroundings (catatonia) (American Psychiatric Association, 2000).

Psychosis has many etiologies. The Diagnostic and Statistical Manual-IV Text Revision (DSM-IV TR) (American Psychiatric Association, 2000) distinguishes between primary psychotic disorders and those due to other etiologies. Primary psychotic disorders include schizophrenia, delusional disorders, schizoaffective disorder, schizophreniform disorder, and brief psychotic disorder. By contrast, psychosis can be due to a general medical condition such as Dementia of the Alzheimer's Type (DAT) or traumatic brain injury (TBI), a psychoactive substance such as amphetamines or cannabis, or secondary to a mood disorder such as major depression. The following are brief descriptions of the DSM-IV TR diagnostic criteria for each disorder:

Diagnostic criteria for schizophrenia

1. A. Two or more of the following symptoms are present: (1) delusions, (2) hallucinations, (3) disorganized speech, (4) grossly disorganized or catatonic behavior, and (5) negative symptoms.

2. […]

Psychotic disorders of different etiologies have interested both clinicians and researchers, but for different reasons. People with psychosis have been some of the most challenging for clinicians to treat due to the severity and chronicity of symptoms. One potential problematic aspect of treatment is differential diagnosis as psychosis can result from numerous etiologies and many patients have more than one risk factor. A review of the presentation, course and progression, and optimal treatment strategies would certainly be useful for clinicians in making these determinations.

For researchers and theoreticians, secondary or “organic” psychotic disorders can provide clues to underlying neurobiological mechanisms of schizophrenia or psychosis in general. Unfortunately, thus far, this potential avenue of research has not been adequately explored. One problem is that the literature on the “so called” secondary psychotic disorders is not readily available for study or review. There are many different etiologies, thus amassing this disparate literature would take a concerted effort. In addition, much of the information on “organic psychosis,” particularly for the obscure etiologies, is provided in case studies or case series, many in difficult-to-find journals. We believe these problems in access to information have prevented researchers from mining this rich resource.

The purpose of this book is to address the needs of both clinician and researcher by providing comprehensive reviews of psychotic disorders of different etiologies in one handy resource. For clinicians faced with difficult and fascinating differential diagnoses, this compendium allows quick comparisons useful for diagnostic decision-making.

Introduction

In this chapter we integrate the information on the spectrum of psychotic disorders. First, we summarize data from each of the nine sections. Second, we examine whether the collective data supports our neurobiological hypothesis of psychosis. Next, we utilize the collective data to update our conceptual framework for developing a psychosis. Fourth, implications for DSM-IV diagnostic criteria for psychosis are discussed. Fifth, we report limitations of the data as it relates to psychosis as a neurobiological syndrome. We conclude the chapter and the book by proposing future studies to further elucidate the phenomenon of psychosis. To promote clarity and avoid redundancy, material cited by chapter authors will not be referenced. Instead, readers are encouraged to refer to each chapter for specific citations.

Epidemiology

The epidemiology of psychotic disorders associated with different etiologies is wide ranged, varying from less than 1% of the overall population for acute and transient psychosis, to up to 84% of patients with Lewy body dementia. Prevalence rates appear to be related to the type of disorder and its neurobiology, although variability exists within each group of disorders.

The group with the smallest prevalence rate, around 1% of the general population, is comprised of “primary” psychotic disorders including schizophrenia, schizoaffective disorder (SAD), delusional disorder (DD), and brief psychotic disorder (BPD).

Neurological disorders that are commonly associated with temporal lobe pathology or white matter lesions have estimated prevalence rates of psychosis ranging from 1–15%.