Diagnosis

The doctor will use one or more verbal screening tests to help determine whether a patient's symptoms meet the criteria for schizophrenia. Because no single symptom is specific to schizophrenia, a diagnosis may be made when one or more of the following conditions is present:

• If a patient has at least one active flare-up lasting a month or less. The flare-up consists of at least two characteristic symptoms (such as hallucinations, delusions, evidence of disorganized thinking, and emotional unresponsiveness with a flat speaking tone).
• If the patient has particularly bizarre delusions or hallucinations even in the absence of other characteristic symptoms.
• If certain symptoms are present for at least 6 months even in the absence of active flare-ups. Such symptoms include marked social withdrawal, peculiar behavior (talking to oneself, severe superstitiousness), vague and incoherent speech, or other indications of disturbed thinking. The patient's social and personal relationships would also have deteriorated since the onset of symptoms.

Possible Markers of Schizophrenia

Experts are investigating tests of specific phenomenon that might suggest a higher risk for or even the presence of schizophrenia.

• Eye Tracking Dysfunction. A dysfunction in eye tracking is a genetic trait that is strongly associated with schizophrenia and may reflect abnormalities in the frontal regions of the brain. (Some experts believe that this is such a powerful marker in patients with close relatives with schizophrenia that it can be used as a predictor. This trait can only be detected by a health professional using special equipment.)
• Impaired Prepulse Inhibition. Prepulse inhibition (PPI) is a phenomenon in which a weak stimulus (such as a low sound) that occurs before a strong stimulus (such as a loud sound) reduces the startle response to it. PPI is impaired in schizophrenia.

Ruling Out Other Conditions

The common hallmarks of schizophrenia are also symptoms that can occur in dozens of other psychologic and medical conditions, as well as with certain medications. Shared symptoms include delusions, hallucinations, disorganized and incoherent speech, a flat tone of voice, and bizarrely disorganized or catatonic behavior (such as lack of speech, muscular rigidity, and unresponsiveness).

Among the conditions that may resemble schizophrenia are the following:

• Depression. Delusions that focus on a physical abnormality or disease that isn't real, known as somatic delusions, sometimes occur in people with depression.
• Bipolar Disorder. Paranoia and delusions of grandeur (the belief that one has a special power or mission) can occur in people with bipolar disorder during the manic phase. In fact, sometimes it is difficult even for experts to differentiate between these two disorders. Evidence suggests that they may share certain genetic factors that make some families vulnerable to either one.
• Schizophrenia-Like Psychoses. There are a number of conditions that exhibit schizophrenia-like psychoses but do not meet the diagnostic criteria for schizophrenia. Such conditions may be variations of entirely different diseases and are classified at this time as schizoaffective disorder, schizophreniform psychosis, and atypical and brief reactive schizophrenia.
• Alcohol and Drug Abuse. Either substance abuse itself or withdrawal from drugs or alcohol can also trigger psychosis. Because of the high risk for substance abuse among people with schizophrenia, it is important that the health professional distinguish psychosis triggered by drugs or alcohol from a schizophrenic episode. Usually, the diagnosis is confirmed if the psychosis ends after withdrawal from drugs or alcohol, and returns if the patient returns to alcohol or substance abuse.
• Medical Illnesses. Other causes of psychotic symptoms include cancer in the central nervous system, encephalitis, neurosyphilis, thyroid disorders, Alzheimer's disease, epilepsy, Huntington's disease, multiple sclerosis, stroke, Wilson's disease, some vitamin B deficiencies, and systemic lupus erythematosus.
• Medication Reactions. Many medications may induce psychosis as a side effect, and some can precipitate delusions and severe confusion. Such medication-induced symptoms are most often observed in elderly patients.

Imaging Techniques

A number of brain imaging techniques are becoming useful in detecting changes in the brain structure that relate to specific sets of symptoms in schizophrenia. At this time such techniques are used only as research tools, although some experts believe they may be useful for identifying candidates for early treatment among high-risk young people with early warnings signs of schizophrenia and brain damage.

Magnetic Resonance Imaging. Magnetic resonance imaging (MRI) has become a particularly valuable tool for revealing parts of the brain inaccessible to other scanning methods. MRI does not use radiation, and it can show the brain from a number of different perspectives.

Other Imaging Techniques. Other imaging techniques are single photon emission computed tomography (SPECT) and positron emission tomography (PET), which can provide information on blood flow and metabolism in the brain.

Investigative Tests

Research is ongoing to find simple tests that will detect schizophrenia accurately and early enough to initiate preventive measures. Some examples include:

• An investigative test that uses computers to analyze brain scans and identify changes in blood flow indicative of schizophrenia, even before symptoms occur. It appears to be highly reliable. More research is needed.
• A blood test that detects genetic evidence of high levels of D3 dopamine receptor may prove to useful. People with schizophrenia have over three times the normal amount of this substance.
• Measurements of certain esters (phosphomonoesters and phosphodiesters) may detect high-risk individuals.