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Diagnosis of Delusional Disorder

Delusional Disorder is diagnosed based on a clinical assessment performed by a mental health professional, usually a psychiatrist.  This assessment includes an interview with the individual, a review of any previous assessments in their medical records, and can also include an interview with the individual's family members or close friends.  The goal of this assessment is to determine whether the individual meets the clinical criteria for Delusional Disorder based on the information obtained. 

There are no laboratory tests or imaging tests (such as CT scans or MRI scans) that can help make a diagnosis of Delusional Disorder. However, these sorts of tests are often important in order to determine whether a general medical condition or the effects of a particular substance may be contributing to, or causing, the delusions.

Differential Diagnosis of Delusional Disorder

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

Medical causes of delusions

In theory any form of damage or insult to the brain could cause delusions. 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 delusions

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

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

Most of the time, if the above substances and medications cause delusions, this will 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 Delusional Disorders

Delusional Disorder should be distinguished from other Psychotic Disorders and from Mood Disorders with psychotic features. See here for further information.

When Somatic Type Delusional Disorder involves the false belief that there are gross defects of one's appearance, this may in fact reflect Body Dysmorphic Disorder. In these cases, the DSM-IV-TR recommends that individuals be diagnosed with both Body Dysmorphic Disorder and Delusional Disorder, though some experts argue that Body Dysmorphic Disorder can include delusional variants, and that Delusional Disorder need not be diagnosed in these cases [ref].

Hypochondriasis is a condition that also involves the exaggerated belief that one is suffering from a serious and undiagnosed illness. When these belief reach delusional proportions, Somatic Type Delusional Disorder is the preferred diagnosis.

Paranoid Personality Disorder may be characterized by beliefs that one is being persecuted, but in this case these beliefs will not be totally fixed but rather could be challenged and reasoned with.

Symptoms & Definition