Organic mental disorder

Alternative names
OBS; Organic brain syndrome; Chronic organic brain syndrome

Organic brain syndrome is a general term referring to physical disorders (usually not psychiatric disorders) that cause decreased mental function.

Causes, incidence, and risk factors
OBS is a common diagnosis in the elderly. It is not an inevitable part of aging, however. OBS is not a separate disease entity, but is a general term used to categorize physical conditions that can cause mental changes.

Disorders associated with OBS include, but are not limited to:

  • Degenerative disorders:       o Creutzfeldt-Jacob disease       o Huntington disease       o Multiple sclerosis       o Normal pressure hydrocephalus       o Pick disease       o Senile Dementia, Alzheimer type  
  • Cardiovascular disorders:       o Arrhythmias - may cause some types of OBS       o Cardiac infections (endocarditis, myocarditis, etc.) - may sometimes cause OBS       o Hypertensive brain injury       o Multi-infarct dementia (multiple strokes)       o Stroke       o TIA  
  • Trauma-induced brain injury:       o Chronic subdural hematoma (blood clot causing pressure on brain)       o Concussion       o Intracerebral hemorrhage       o Subarachnoid hemorrhage  
  • Dementia due to metabolic causes  
  • Respiratory conditions - may cause or aggravate OBS       o Hypoxia (decreased oxygen in the body)       o Hypercapnia (increased carbon dioxide levels in the body)  
  • Infections       o Any acute or chronic infection       o Septicemia (presence in the bloodstream of toxic by-products caused by infection)       o Meningitis       o Encephalitis  
  • Drug and alcohol related conditions       o Intoxication, drug abuse, or alcohol use       o Long-term effects of alcohol, Wernicke-Korsakoff syndrome       o Alcohol withdrawal state       o Withdrawal from drugs (especially sedative-hypnotics and corticosteroids)  
  • Parkinson’s disease

Other conditions that may be related to organic brain syndrome include: Depression, neuroses, and psychoses of various types, which may occur simultaneously with the OBS.

Symptoms vary with the specific disease. In general, organic brain syndromes cause varying degrees of confusion, delirium (severe, short-term loss of brain function), agitation, and Dementia (long-term, often progressive, loss of brain function).

Signs and tests
Testing and physical examination vary depending on the specific disorder.


Treatment varies with the specific disorder. Many of the disorders have nonspecific treatments - primarily supportive care to assist the person in areas where brain function is lost.

Medications may be needed to reduce aggressive behaviors typical of some of the conditions in this category.

Expectations (prognosis)
See the specific disorder. Some disorders are acute and treatable, but many are chronic or progressive.

Loss of ability to interact or function independently is common.

Calling your health care provider

Call your provider if:

  • Organic brain syndrome has been diagnosed and you are uncertain of the actual, specific diagnosis  
  • You have symptoms which suggest this problem  
  • You have been diagnosed with OBS and symptoms become worse

Johns Hopkins patient information

Last revised: December 3, 2012
by Levon Ter-Markosyan, D.M.D.

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