Mild Cognitive Impairment in the Elderly

 The presence of mild cognitive impairment (MCI) in elderly individuals is often a clinical challenge of uncertain prognostic value.  Defined as cognitive function below the normal range but insufficient for a diagnosis of dementia, MCI is receiving increased research attention.  This week in the New England Journal of Medicine, Dr. Ronald Petersen, a neurologist from the Mayo Clinic in Rochester, Minnesota highlighted what is known about MCI.  His review summarizes some of the recent research related to MCI as well as some issues in clinical assessment and management.

Dr. Petersen noted that MCI is typically separated into two categories.  The first is amnestic MCI where memory impairment is predominant.  The second is nonamnestic MCI where deficits in other domains such as language, attention or visuospatial function.

Prevalence (70-89 year old non-dementia sample)

• 11.1% amnestic MCI
• 4.9% nonamnestic MCI

Amnestic MCI may be harbinger of Alzheimer's disease

Nonamnestic MCI may be harbinger of frontotemperal lobe degeneration or dementia with Lewy bodies

Risk of dementia in elderly about 1% to 2% per year

Risk for those with MCI raised to 5% to 10% per year

Assessment

•     Brief Minimental Status Exam (MMSE) often insensitive to early impairment
•     Better tools include the Short Test of Mental Status and Montreal Cognitive Assessment
•     Comprehensive neuropsychological testing necessary for definitive diagnosis and severity rating

Mild cases may be due to depression or the cognitive effects of medication

Differentiating from dementia primarily by level of functional impairment

This may be assessed using the Functional Activities Questionnaire

Predictors of progression of amnestic MCI to dementia (primarily research tools at this point)

•     More severe MCI
•     Presence of the Apolipoprotein epsilon 4 gene
•     Hippocampal volume less than the 25%tile for age by magnetic resonance imaging
•     PET imaging shows temporal and parietal brain hypometabolism
•     Cerebrospinal fluid assay shows low beta amyloid 42 to tau protein ratio
•     Brain amyloid plaques on PET imaging using Pittsburgh compound B

Treatment--No medication approved by FDA for treatment of MCI

• Alzheimer's drugs donepezil, galantamine and rivastigmine have negative placebo-controled clinial trial results in MCI.  Donepezil but not Vitamin E reduced progression to Alzheimers disease in MCI in one trial for first two years but not at three years of treatment
• Some evidence that cognitive rehabilitation may be helpful in short term improvement of memory in MCI
• Treat reversible cardiovascular risk factors if they are present
• Encourage brisk walking exercise 150 minutes per week

Given that 15% of elderly individuals demonstrate a form of MCI, it is likely this condition will generate significant ongoing research interest.  An intervention that would reduce the risk of progression of dementia after the onset of MCI would be a major advance in the prevention of Alzheimer's Disease.

Dr. Petersen provides copies of the Short Test of Mental Status, the Montreal Cognitive Assessment and the Functional Activities Questionnaire in an online appendix to the review.  Readers who do not have access to the online New England Journal of Medicine can contact me for alternate options to receive copies of the instruments. 

Photo of PET scan of patient with Alzheimer's Disease showing reduced glucose metabolism in the temporal lobes courtesy of Wikipedia Commons file from the National Institute on Aging,  Alzheimer's Disease Education and Referral Center.   
 

Petersen, RC (2011). Mild Cognitive Impairment New Engl J Med, 364, 2227-2234