Mild cognitive impairment

Mild cognitive impairment (MCI, also known as incipient dementia, or isolated memory 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.^[1] It is often found to be 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.^[2] Studies suggest that these individuals tend to progress to probable Alzheimer’s disease at a rate of approximately 10% to 15% per year.^[2]

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 (e.g., dementia with Lewy bodies).^[3] 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,^[2] 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:^[4]

1. Evidence of memory impairment
2. Preservation of general cognitive and functional abilities
3. 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.^[5]

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.^[6] 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.^[7] 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. However, several potential treatments are still under investigation.^[2] 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 on cognitive function for individuals with mild cognitive impairment,^[8] and donepezil showed only minor, short-term benefits and was associated with significant side effects.^[9]

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,^[10] dementia, and cardiovascular disease.^[11][12][13]

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