Numerous changes occur in the brain structure and function with age. These include loss of brain cells, reduced transmission of impulse from the brain and deposition of end-products of metabolism of brain cells. Despite these changes normal older brain is quite capable of learning and remembering. However, in some individuals these age-related changes are excessive with significant functional impairment, which is termed as cognitive impairment.
The clinical features of an aged brain are subtle or manifest alterations in cognition and behaviour. Some amount of forgetfulness is common in older people which is termed as “age-associated memory impairment”.
Age-associated memory impairment usually appears after 50 years of age and is associated with gradual onset of memory dysfunction which can be substantiated by appropriate tests. However, the intellectual function is usually intact with no evidence of any neurological deficit.
In contrast, dementia is a severe and pathological form of cognitive impairment. It is a clinical syndrome characterized by persistent impairment of multiple cognitive capacities, associated with a variety of behavioural problems.
Several pathological conditions cause dementia which include Alzheimer’s disease, Lewy body dementia, Parkinson’s disease and vascular dementia.
Chronic alcoholism, deficiency of thyroid hormone, vitamin B12 deficiency, infections and injury are responsible for cognitive impairment in a small number of cases.
Symptoms of dementia include gradual memory loss, decline in the ability to perform routine tasks, disorientation, difficulty in learning, loss of language skills, impairment of judgement and planning, and personality changes. The rate of progression varies from person to person and from cause to cause. In Alzheimer’s disease the time from the onset of symptoms untill death is about eight years but can vary from three to twenty years.
Cognitive impairment of normal ageing produces little disability and can be easily distinguished from dementia even early in the disease. Some clues to differentiation are presented in the accompanying box.
|Activity||Dementia||Age- associated Memory Problems|
|Forgets||Whole Experience||Parts of an experience|
|Can use notes||Gradually unable||Usually able|
|Can care for self||Gradually unable||Usually able|
|Can follow written or spoken instructions||Gradually unable||Usually able|
However, it is important that careful evaluation is carried out to exclude treatable causes of cognitive impairment which include depression, adverse drug reaction, metabolic diseases and nutritional deficiencies.
There is no single test to diagnose Alzheimer’s disease and other dementias. A definitive diagnosis requires the demonstration of characteristic pathological changes in the brain tissue which is rarely carried out. However, a probable diagnosis of dementia can be made on the basis of well-defined guidelines.
The evaluation for diagnosis includes careful clinical examination, assessment of mental state, routine biochemical tests of blood, imaging of brain (CT scan and MRI scan) and a battery of neuropsychological tests.