Diagnostic Criteria

Screening

A physician can use verbal screening tests to determine whether symptoms meet the criteria for schizophrenia. Because there is no single schizophrenic symptom, a diagnosis usually depends on a person having at least one active flare-up that consists of two characteristic symptoms (i.e. hallucinations, delusions, disorganized thinking, emotional unresponsiveness, etc.).  If the patient has delusions or hallucinations that are particularly bizarre, a diagnosis is sometimes made from just this one symptom.  Diagnosis, in the absence of active flare-ups, look for marked social withdrawal, peculiar behavior (like talking to oneself, or severe superstitiousness), or vague and incoherent speech, which must be present for at least six months.

Other Conditions

Common characteristics of schizophrenia include delusions, hallucinations, incoherent and disorganized speech, a flat tone of voice, and unusually disorganized or catatonic behavior, such as lack of speech, or muscular rigidity and unresponsiveness.  However, there are a number of schizophrenia-like psychoses that may be variations of entirely different diseases. These variations are classified for now as schizoaffective disorder, atypical or brief reactive schizophrenia, and schizophreniform psychosis. For example, in schizoaffective disorder, people have psychotic episodes in between full manic or depressed periods.

Alcohol and drug abuse, or withdrawal from, can also cause psychosis. Because schizophrenics have a high risk for substance abuse, it is important that psychosis triggered by drugs or alcohol is distinguished from a schizophrenic episode. This diagnosis is usually confirmed if psychosis ends after withdrawal from drugs or alcohol, and then returns when the patient resumes alcohol or drug abuse.

There are many other causes of psychotic symptoms: cancer in the central nervous system, encephalitis, neurosyphilis, thyroid disorders, Alzheimer's disease, complex partial seizures, Huntington's disease, multiple sclerosis, stroke, Wilson's disease, some vitamin B deficiencies, and systemic lupus erythematosus.

Even some medications bring on psychosis as a side effect, and some can trigger delusions or severe confusion. These medication-induced symptoms are usually observed in elderly patients.

Imaging

Brain imaging techniques are useful in determining if parts of the brain are damaged and whether the damage relates to a specific set of symptoms. Magnetic resonance imaging (MRI) is a particularly valuable tool for revealing parts of the brain, as is some other new imaging techniques, like single photon emission computed tomography (SPECT) and positron emission tomography (PET) (which can provide information on the brain’s blood flow and metabolism).