Organic Brain Syndrome

Organic brain syndrome (OBS), also known as organic brain disease (OBD) Organic mental disorders organic brain disorder, is an older and nearly obsolete general term from psychiatry, referring to many physical disorders that cause impaired mental function. It does not include psychiatric disorders. Originally, the term was created to distinguish physical (termed "organic") causes of mental impairment from psychiatric (termed "functional") disorders.

Acute organic brain syndrome is (by definition) a recently appearing state of mental impairment, as a result of intoxication, drug overdose, infection, pain, and many other physical problems affecting mental status. In medical contexts, "acute" means "of recent onset". As is the case with most acute disease problems, acute organic brain syndrome is often temporary–however this is not guaranteed (a recent-onset problem may continue to be chronic or long term). A more specific medical term for the acute subset of organic brain syndromes is delirium.

Chronic organic brain syndrome is long-term. For example, some forms of chronic drug or alcohol dependence can cause organic brain syndrome due to their long-lasting or permanent toxic effects on brain function. Other common causes of chronic organic brain syndrome sometimes listed are the various types of dementia, which result from permanent brain damage due to strokes, Alzheimer's disease, or other damaging causes which are not reversible.

Though OBS was once a common diagnosis in the elderly, until the understanding of the various types of dementias it is related to a disease process and is not an inevitable part of aging. In some of the older literature, there was an attempt to separate organic brain syndrome from dementia, but this was related to an older world view in which dementia was thought to be a part of normal aging, and thus did not represent a special disease process. The later identification of various dementias as clear pathologies is an example of the types of pathological problems discovered to be associated with mental states, and is one of the areas which led to abandonment of all further attempts to clearly define and use OBS as a term.