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Diseases reference index «Organic brain syndrome»

Organic brain syndrome

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


Disorders associated with OBS include:

  • Brain injury caused by trauma
    • Bleeding into the brain (intracerebral hemorrhage)
    • Bleeding into the space around the brain (subarachnoid hemorrhage)
    • Blood clot inside the skull causing pressure on brain (subdural hematoma)
    • Concussion
  • Breathing conditions
    • Low oxygen in the body (hypoxia)
    • High carbon dioxide levels in the body (hypercapnia)
  • Cardiovascular disorders
    • Abnormal heart rhythm (arrhythmias)
    • Brain injury due to high blood pressure (hypertensive brain injury)
    • Dementia due to many strokes (multi-infarct dementia)
    • Heart infections (endocarditis, myocarditis)
    • Stroke
    • Transient ischemic attack (TIA)
  • Degenerative disorders
    • Alzheimer's disease (also called senile dementia, Alzheimer's type)
    • Creutzfeldt-Jacob disease
    • Diffuse Lewy Body disease
    • Huntington's disease
    • Multiple sclerosis
    • Normal pressure hydrocephalus
    • Parkinson's disease
    • Pick's disease
  • Dementia due to metabolic causes
  • Drug and alcohol-related conditions
    • Alcohol withdrawal state
    • Intoxication from drug or alcohol use
    • Wernicke-Korsakoff syndrome (a long-term effect of excessive alcohol consumption or malnutrition)
    • Withdrawal from drugs (especially sedative-hypnotics and corticosteroids)
  • Infections
    • 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)
  • Other medical disorders
    • Cancer
    • Kidney disease
    • Liver disease
    • Thyroid disease (high or low)
    • Vitamin deficiency (B1, B12, or folate)

Other conditions that may mimic organic brain syndrome include:

  • Depression
  • Neurosis
  • Psychosis


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

  • Agitation
  • Confusion
  • Long-term loss of brain function (dementia)
  • Severe, short-term loss of brain function (delirium)

Exams and Tests

Tests depend on the disorder, but may include:

  • Blood tests
  • Electroencephalogram (EEG)
  • Head CT scan
  • Head MRI


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)

See the specific disorder. 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

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