Other Dementia
Mild Cognitive Impairment
Mild cognitive impairment (MCI) is a general term most commonly defined as a subtle but measurable memory disorder. A person with MCI experiences memory problems greater than normally expected with aging, but does not show other symptoms of dementia, such as impaired judgment or reasoning.
The American Academy of Neurology (AAN) published practice guidelines for the early detection of memory problems in 2001 and identified the following criteria for an MCI diagnosis:
- an individual’s report of his or her own memory problems, preferably confirmed by another person
- measurable, greater-than-normal memory impairment detected with standard memory assessment tests
- normal general thinking and reasoning skills
- ability to perform normal daily activities
Some research suggests that essentially all cases of MCI progress to Alzheimer’s disease or another form of dementia. This would mean that MCI is simply a very early sign of dementia. Other studies suggest that some people with MCI may not develop dementia, but that many are at a very high risk of developing the disorder. Still other studies indicate that a significant number of people diagnosed with MCI may “revert” to normal.
Because there is a lack of agreement about a definition, any two individuals with a diagnosis of MCI may have relatively significant differences in symptoms. Physicians’ recommendations for treatment will also vary. At this time, there is no widely accepted professional guideline for treatment of MCI and there is not enough evidence to recommend a standard approach. In most cases, if a person is diagnosed with MCI, the physician will regularly monitor the individual for changes in memory and thinking skills that indicate a worsening of symptoms or a development of mild dementia.
Age-Associated Memory Impairment
Aging causes deterioration of various aspects of human physiology including a decline in cognitive performance and memory. Memory impairment has been detected and measured in the elderly with several standardized tests, including the Wechsler Memory Scale (WMS), the immediate and delayed Visual Reproduction Test, the Rey Auditory Verbal Learning Test (RAVLT), and others.
To characterize memory loss more systematically, the National Institute of Mental Health (NIMH) created a working group that proposed a criteria for defining “age-associated memory impairment” (AAMI). These criteria include: complaints of memory loss in persons over the age of 50, impairment on a standardized memory test one standard deviation below that of young adults, and absence of dementia or other medical conditions that could produce cognitive deterioration. Because AAMI is related to “normal” aging, its prevalence is expected to be as high as 50% of all individuals above the age of 50.
The causes of AAMI remain poorly understood: some have attributed its development to general oxidative cellular damage, while others have postulated that it may be associated with a decline in the brain's ability to utilize glucose. Recently, studies have shown that the gene that produces insulin degrading enzyme (IDE) may play an important role in cerebral glucose hypometabolism, and subsequently, in the development of memory impairment.