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Diagnosing Schizophrenia

Schizophrenia is diagnosed based on a clinical assessment performed by a physician, usually a psychiatrist.  This assessment usually includes an interview with the patient and a review of any previous assessments in their medical records, and can also include an interview with the patient's family members or close friends.  The goal of this assessment is to determine whether the patient meets the clinical criteria for Schizophrenia based on the reports that they or their family members and friends provide.  Sometimes it is not possible to arrive at a definitive diagnosis of the disorder from a single clinical interview, and a period of observation either in hospital or as an out-patient may be required.

There are no laboratory tests or imaging tests (such as CT scans or MRI scans) that can help make a diagnosis of Schizophrenia.  However, these sorts of tests are often important in order to rule-out any other general medical conditions that may be associated with the condition.

Clinicians who treat people with Schizophrenia should also examine their patients for any cognitive deficits. Some basic clinical tests for this purpose can be found here.

Differential Diagnosis of Schizophrenia

There are various medical and psychiatric conditions that can cause psychotic symptoms and that should be distinguished from Schizophrenia.

Medical causes of psychosis

In theory any form of damage or insult to the brain could cause psychosis. Most of the time, this will occur in the context of a delirium, and there will also be many other physical signs and symptoms to suggest that there is something wrong medically. Medical problems that can affect the brain include:

  • Tumors
  • Strokes
  • Infections (eg. HIV/AIDS, Syphilis, Herpes)
  • Inflammation (eg. Systemic Lupus Erythematosus, Multiple Sclerosis)
  • Electrolyte and nutrient imbalances (eg. sodium and calcium imbalance, Wilson's Disease, liver failure, deficiencies of Folate, Niacin, Thiamine, and Vitamin B12)
  • Degenerative diseases (eg. Dementia, Parkinson's Disease, Huntington's Disease)
  • Endocrine diseases (eg. Cushing's Syndrome, thyroid imbalances)
  • Paraneoplastic syndrome

Substances that can cause psychosis

Various street drugs and substances of abuse can cause psychosis, including:

Many kinds of medications can also cause psychotic symptoms. The ones that are most likely to do this include:

Most of the time, the above substances and medications will cause psychotic symptoms only for a few hours or days - the time it takes for the substance to clear from the brain. However, corticosteroids can trigger psychotic symptoms that can last for weeks after the drug has been stopped [ref]. Long-term, heavy marijuana use has been found to increase the risk of developing Schizophrenia (see here for further information).

Psychiatric conditions that can be mistaken for Schizophrenia

Diagnostic Tools for Schizophrenia

Sometimes, clinicians may use scales and questionnaires based on clinical interviews to help identify patients with Schizophrenia and to document the severity of their patient's symptoms.   These include:

The Brief Psychiatric Rating Scale (BPRS) measures psychotic and non-psychotic symptoms in people with a major psychiatric disorder, and has been most commonly used with Schizophrenia.  The scale is completed by a clinician based on a clinical interview, and gives a rating of the person's overall level of symptoms.

The Positive and Negative Symptom Scale for Schizophrenia (PANSS) is used to evaluate the presence of positive and negative symptoms in an individual with Schizophrenia and is rated by a clinician based on a clinical interview.   

There are several scales available for evaluating the presence of extrapyramidal symptoms.  These scales are all rated by a physician based on a physical examination of the patient's voluntary and involuntary movements.

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Extrapyramidal Symptoms

Detecting Cognitive Deficits