Alzheimer's disease

A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from prior levels of function and interferes with the ability to perform routine daily activities (for example, balancing a checkbook or remembering appointments).

Alzheimer's disease is the most common form of dementia, affecting 5% of individuals over age 65. The onset of the dementia typically occurs in middle to late life, and the prevalence of the illness increases with advancing age to include 25-35% of individuals over age 85.
Memory loss, including difficulty in remembering recent events and learning new information, is typically the earliest clinical feature of Alzheimer's disease. As the illness progresses, memory of remote events and overlearned information (for example, date and place of birth) declines together with other cognitive abilities.

In the later stages of Alzheimer's disease, there is increasing loss of cognitive function to the point where the individual is bedridden and requires full-time assistance with basic living skills (for example, eating and bathing). Behavioral disturbances that can accompany Alzheimer's disease include agitation, aggression, depressive mood, sleep disorder, and anxiety.

The major neuropathological features of Alzheimer'sdisease include the presence of senile plaques, neurofibrillary tangles, and neuronal cell loss. Although the regional distribution ofbrain pathology varies among individuals, the areas commonly affected include the association cortical and limbic regions.
Deficits in cholinergic, serotonergic, noradrenergic, and pep-tidergic (for example, somatostatin) neurotransmitters have been demonstrated. Dysfunction of the cholinergic neurotransmitter system has been specifically implicated in the early occurrence of memory impairment in Alzheimer's disease, and it has been a target in the development of potential therapeutic agents.
A definite diagnosis of Alzheimer's disease is made only by direct examination of brain tissue obtained at autopsy or by biopsy to determine the presence of senile plaques and neurofibrillary tangles. A clinical evaluation, however, can provide a correct diagnosis in more than 80% of cases.

The clinical diagnosis of Alzheimer's disease requires a thorough evaluation to exclude all other medical, neurological, and psychiatric causes of the observed decline in memory and other cognitive abilities.
Although the cause of Alzheimer's disease is unknown, a number of factors that increase the risk of developing this form of dementia have been identified. Age is the most prominent risk factor, with the prevalence of the illness increasing twofold for each decade of life after age 60. Research in molecular genetics has shown that Alzheimer's disease is etiologically heterogeneous. Gene mutations on several different chromosomes are associated with familial inherited forms of Alzheimer's disease.

A major strategy for the treatment of Alzheimer's disease has focused on the relation between memory impairment and dysfunction of the acetylcholine neurotransmitter system. other treatment strategies to delay or diminish the progression of Alzheimer's disease are being explored. Behavioral and pharmacological interventions are also available to treat the specific behavioral disturbances that can occur in Alzheimer's disease.