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Schizophrenia is a pervasive, debilitating disease characterized by positive symptoms of hallucinations, delusions, and thought disorder (also referred to as psychosis), and negative symptoms of chronic social dilapidation. Emil Kraepelin first distinguished schizophrenia (then termed dementia praecox) from bipolar psychosis more than 100 years ago, by contrasting the long-term deteriorating course of delusions and hallucinations characteristic of schizophrenia to the intermittent course of bipolar illness. Schizophrenia remains a clinical diagnosis made on the basis of the individual's psychiatric history and mental status examination, as no laboratory or imaging studies can validly diagnose it.

Inclusion Criteria

Schizophrenia is described in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders as two or more of the following symptoms active for a minimum of 1 month's duration (unless adequately treated) as well as the continuing presence of a symptom for 6 months: delusions, hallucinations, disorganized speech, disorganized behavior, and negative symptoms along with a significant disturbance of the individual's functioning that results in disturbances in occupation, social interaction, or the management of one's self-care. These symptoms of schizophrenia can be characterized as either positive or negative.

Positive Symptoms

The positive symptoms of schizophrenia consist of abnormalities of sensory experience and cognitive processing. These manifest as hallucinations, delusions, bizarre behavior, or formal thought disorder. Hallucinations are perceptions in the absence of physical stimuli. In schizophrenia, auditory hallucinations usually predominate, but, in patients with late-onset schizophrenia, olfactory, visual, tactile, or gustatory hallucinations may be present. In schizophrenia, the hallucinated voices are described as coming from outside the person's head and providing a running commentary on the patient's behavior. At times, these speak directly to the individual or converse with each other. Voices that tell the individual what to do are referred to as command hallucinations.

Delusions are fixed, false, idiosyncratic beliefs and consist of ideas and beliefs that are persecutory, bizarre, or grandiose. The idea that the person is being controlled by outside forces is common.

Bizarre behavior may be observed in the person's appearance (odd/inappropriate layering of clothing) or in their aggressive, agitated or repetitive/stereotyped behavior (for example, flipping the light switch multiple times or repeated closing and opening the door). Formal thought disorder includes illogical or incoherent speech in the absence of aphasia. It manifests as tangentiality, loose associations (a lack of logical connection between sentences), or derailment (the sudden loss of train of thought).

Negative Symptoms

The negative symptoms of schizophrenia result in a decline in the person's baseline social, interpersonal, and volitional activity. People with schizophrenia often have a diminished range of facial expression, a phenomenon termed affective flattening; poor eye contact, and decreased expressive gesturing. Spontaneous speech decreases and speech latency increases. Individuals with schizophrenia become less social and form few close relationships with others. As the disease progresses, avolition and apathy become common ...

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