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What are Organic Brain disorders?

Introduction

Organic Brain Disorders are conditions that are due to damage or deterioration of brain tissue. An alternative term is “Neuro-psychiatric Disorders.”

Cognition is frequently affected but they may present as a behavioural or emotional disturbance.

Cognition is a broad term that refers to all the processes involved in perceiving, learning, remembering and thinking. Cognitive function can be assessed by a variety of methods. Although there are a variety of assessment tools, one of the most frequently used is the Mini Mental State Examination, which covers the following areas:

For a list of functions (and definitions) tested by the Mini Mental State Examination please refer to the link below.

Executive function refers to aspects of higher order brain function, such as problem solving, reasoning and mental abstraction. These functions are located in the frontal lobes.

Organic Brain Disorders can be broadly divided into three categories:

Delirium and dementia tend to affect all aspects of cognition i.e. global impairment, whereas specific neuro-psychiatric disorders affect selective components of cognitive function.

Many of these conditions are rarities. This guidance concentrates on those conditions that are most likely to be encountered by the Decision Maker or where there are specific points that merit emphasis.

Delirium (Acute confusional state, acute organic syndrome)

Although Delirium is unlikely to be encountered by the Decision Maker, it is included for completeness.

Delirium is disturbed consciousness with disorientation in time and place, which typically fluctuates over the course of 24 hours.

It is common in people admitted to hospital, especially the elderly and those with reduced “cerebral reserve” due to, for example, pre-existing dementia, head injury, stroke and a history of substance abuse.

Causes include:

Dementia

Dementia is a chronic syndrome characterised by global cognitive impairment without altered consciousness. Some specific types of dementia that are more likely to be more commonly encountered, or which have particular features are detailed later in this section.

There are many causes of dementia. Amongst the elderly, by far the commonest are vascular and degenerative disorders. Early onset (formerly called pre-senile) dementia refers to people less than 65 years of age. In younger age groups, a much wider range of possible causes needs to be considered, so that those that are treatable can be excluded.

The causes can be usefully grouped into the following categories:

For the diagnosis of dementia to be made, two or more of the following cognitive functions must be affected:

The impairment will have reached a level that is starting to have an impact socially, or on the ability to function in the workplace.

The prevalence of dementia increases with age. It is estimated that 5% of people over age 65 and 10 to 20% of people over 80 have dementia.

Alzheimer’s disease

This is the commonest form of dementia. It accounts for 34% of cases in people under 65 and 55% of cases in people over 65.

Risk factors include genetic predisposition, previous moderate or severe head injury as a young adult and Down’s syndrome. The onset is often insidious and there are several stages.

Vascular dementia

In the past this was referred to as multi-infarct dementia. It is thought to be the second commonest form of dementia. It accounts for 18% of cases in people under 65 and 20% of cases in people over 65. It is due to multiple areas of infarction in the brain. It may affect large or small blood vessels. If small blood vessels are affected, there may be no evidence of stroke. It is more common in men and there is a strong association with risk factors for coronary artery disease.

Dementia with Lewy Bodies (DLB)

This accounts for 7% of cases in people under 65 and 20% of cases in people over 65. It has been recognised in people aged between 50 and 83 years with a mean age at onset of 75 years.

Fronto-temporal dementia (Pick’s disease)

This is increasingly recognised as a common cause of dementia, particularly in the younger age group and accounts for 12% of cases in people under 65. The peak incidence of onset is 45 to 65 years of age.

It is characterised by degeneration of the fronto-temporal region of the brain. The cause is unknown but many cases are familial.

AIDS dementia complex (HIV encephalopathy)

Minor cognitive impairment is relatively common in HIV infection, which can produce a wide range of neuro-psychiatric disorders.

The virus can directly invade brain tissue causing AIDS dementia complex. This is usually a later feature of the disease. However, since the introduction of highly active antiretroviral therapy (HAART), AIDS dementia complex has become uncommon.

Prion diseases

These are rare in the UK.

Variant Creutzfeldt-Jacob disease, colloquially known as “mad cow disease” (vCJD) was first described in 1996 and tends to affect younger people. Creutzfeldt-Jacob disease (CJD) affects an older age group, usually 50 to 70 years.

Huntington’s disease

This is an auto-somal dominant condition (half of the children of sufferers will inherit the disease) affecting men and women in equal numbers. Onset is usually in the 30’s. It causes sub-cortical dementia.

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Amended April 2008

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