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Organic brain syndrome

Organic brain syndrome (OBS) is a general term that describes decreased mental function due to a medical disease other than a psychiatric illness. It is often used synonymously (but incorrectly) with dementia.


Listed below are disorders associated with OBS.

Brain injury caused by trauma

Breathing conditions

  • Low oxygen in the body (hypoxia)
  • High carbon dioxide levels in the body (hypercapnia)

Cardiovascular disorders

Degenerative disorders

Dementia due to metabolic causes

Drug and alcohol-related conditions


  • Any sudden onset (acute) or long-term (chronic) infection
  • Blood poisoning (septicemia)
  • Brain infection (encephalitis)
  • Meningitis (infection of the lining of the brain and spinal cord)
  • Prion infections, such as mad cow disease
  • Late-stage syphilis

Complications of cancer can also lead to OBS.

Other conditions that may mimic organic brain syndrome include:


Symptoms can differ based on the disease. In general, organic brain syndromes cause:

Exams and Tests

Tests depend on the disorder, but may include:


Treatment depends on the disorder. Many of the disorders are treated mainly with rehabilitation and supportive care to assist the person in areas where brain function is lost.

Medications may be needed to reduce aggressive behaviors that can occur with some of the conditions.

Outlook (Prognosis)

Some disorders are short-term and treatable, but many are long-term or get worse over time.

Possible Complications

People with OBS often lose the ability to interact with others or function on their own.

When to Contact a Medical Professional

Call your health care provider if:

  • You have been diagnosed with organic brain syndrome and you are uncertain about the exact disorder.
  • You have symptoms of this condition.
  • You have been diagnosed with OBS and your symptoms become worse.

Alternative Names

OBS; Organic mental disorder (OMS); Chronic organic brain syndrome



Apostolova LG, DeKosky ST, Cummings JL. Dementias. In: Daroff RB, Fenichel GM, Jankovic J, Mazziotta JC, eds.Bradley's Neurology in Clinical Practice

Knopman DS. Alzheimer's disease and other dementias. In: Goldman L, Schafer AI, eds.Goldman's Cecil Medicine

Update Date 2/24/2014

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