Schizophrenia - skĭtˌsəfrēˈnēə, group of severe mental disorders characterized by reality distortions resulting in unusual thought patterns and behaviors. Because there is often little or no logical relationship between the thoughts and feelings of a person with schizophrenia, the disorder has often been called "split personality." However, the condition should not be confused with multiple personality, a disorder in which the individual has two or more distinct personalities that dominate at different times.

In 1896, the German psychiatrist Emil Kraepelin grouped what were previously considered unrelated mental diseases under the term dementia praecox. It was not until 1908, however, that an influential essay by Swiss psychiatrist Eugen Bleuler corrected Kraepelin's theory that the disease was an organic brain deterioration and thus incurable. Bleuler introduced the term schizophrenia to replace dementia praecox, emphasizing the dissociative phenomena in the mind and avoiding the implications of early onset and progressive brain deterioration.

Schizophrenic disorders generally begin in the late teenage years or early adulthood and tend to occur in withdrawn, seclusive individuals. The lifetime prevalence worldwide has been estimated to be just under 1%, and the disorder affects 1.5 to 2 million people in the United States alone. Symptoms include disturbances of thought, both in form and content (see delusion), and disturbances of perception, most commonly appearing as visual or aural hallucinations.

There are five major types of schizophrenia listed by the American Psychiatric Association in its Diagnostic and Statistical Manual of Mental Disorders. The most severe are disorganized (hebephrenic) schizophrenia, characterized by hallucinations, delusions, inappropriate laughing and crying, incoherent speech, and infantile behavior; and catatonic schizophrenia, characterized by physical rigidity or hyperactivity. Paranoid schizophrenics can often function relatively normally, although they may be disturbed by persecutory delusions and hallucinations, and they tend to exhibit argumentative behavior. The presence of a combination of symptoms from other types is classified as undifferentiated schizophrenia. Residual schizophrenia is constituted by minor symptoms, which occur as an active episode diminishes.

The cause of schizophrenia is unknown. Genetic factors appear to be involved in producing susceptibility to the condition, with studies among identical twins showing a 30%–50% concordance rate, a figure that has been confirmed by the results of adoption studies. Biochemical research suggests that high levels of the neurotransmitter dopamine, or excessive numbers of receptors for dopamine, may be at the root of schizophrenia. Medical imaging studies have revealed various physical and physiological anomalies in some patients. Other research has focused on mistiming of neural responses to stimuli in the brain. Many researchers maintain that a combination of influences, including such environmental factors as viral illness or malnutrition in the patient's mother during pregnancy, may lead to schizophrenia,

Antipsychotic drugs (see psychopharmacology), sometimes in conjunction with psychotherapy, have greatly improved the treatment of schizophrenia. Hospitalization is sometimes needed initially to provide basic personal needs (safety, food, and hygiene) while acute symptoms are treated. Most patients return to the community with varying degrees of independence and with good prospects for long-term remission of symptoms.

See R. Miller and S. Mason, Diagnosis: Schizophrenia (2002); studies by I. I. Gottesman (1991) and H. Häfner and W. F. Gattaz, ed. (1991).

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