Mild cognitive impairment is a brain function syndrome involving the onset
and evolution of cognitive impairments beyond those expected based on the age
and education of the individual, but which are not significant enough to
interfere with their daily activities. It may occur as a transitional stage
between normal aging and dementia. Although MCI can present with a variety
of symptoms, when memory loss is the predominant symptom it is termed
"amnestic MCI" and is frequently seen as a prodromal stage of Alzheimer's
disease. Studies suggest that these individuals tend to progress to probable
Alzheimer’s disease at a rate of approximately 10% to 15% per year.
Additionally, when individuals have impairments in domains other than memory
it is classified as nonamnestic single- or multiple-domain MCI and these
individuals are believed to be more likely to convert to other dementias.
However, some instances of MCI may simply remain stable over time or even
remit. Causation of the syndrome in and of itself remains unknown, as therefore
do prevention and treatment. Diagnosis
The diagnosis of MCI requires considerable clinical judgement, and as
such a comprehensive clinical assessment including clinical observation,
neuroimaging, blood tests and neuropsychological testing are best in
order to rule out an alternate diagnosis. MCI is diagnosed when there
is: Evidence of memory impairment
Preservation of general cognitive and functional abilities
Absence of diagnosed dementia Neuropathology
There is evidence suggesting that although amnestic MCI patients may not
meet neuropathologic criteria for Alzheimer's disease, patients may be in
a transitional stage of evolving Alzheimer's disease; patients in this
hypothesized transitional stage demonstrated diffuse amyloid in the
neocortex and frequent neurofibrillary tangles in the medial temporal lobe.
There is emerging evidence that magnetic resonance imaging can observe
deterioration, including progressive loss of gray matter in the brain, from
mild cognitive impairment to full-blown Alzheimer disease. A technique known as
PiB PET imaging is used to clearly show the sites and shapes of beta amyloid
deposits in living subjects using a C11 tracer that binds selectively to such
deposits. Such tools may help greatly in assisting clinical research for
therapies. Treatment
There is no proven treatment or therapy for mild cognitive impairment. As MCI
may represent a prodromal state to clinical Alzheimer’s disease, treatments
proposed for Alzheimer’s disease, such as antioxidants and cholinesterase
inhibitors, may be useful. Two drugs used to treat Alzheimer's disease have
been assessed for their ability to treat MCI or prevent progression to full
Alzheimer's disease. Rivastigmine failed to stop or slow progression to
Alzheimer's disease or to improve cognitive function for individuals with
mild cognitive impairment, and donepezil showed only minor, short-term benefits
and was associated with significant side effects.
In a two-year randomized trial of 168 people with MCI given either high-dose
vitamins or placebo, vitamins cut the rate of brain shrinkage by up to half.
The vitamins were the three B vitamins folic acid, vitamin B6, and vitamin B12,
which inhibit production of the amino acid homocysteine. High blood levels of
homocysteine are associated with increased risk of cognitive decline,
dementia, and cardiovascular disease. Non-pharmacological experimental
treatments include transcranial magnetic stimulation and transcranial direct
current stimulation. References
External links MCI information from the UCSF Memory and
Aging Center Mild cognitive impairment Alzheimer's
Society fact sheet Topic Sheet on Mild Cognitive Impairment