Mild Cognitive Impairment 

  • Author: Heather S Anderson, MD; Chief Editor: Michael Hoffmann, MBBCh, MD, FCP(SA), FAAN, FAHA   more...
 
Updated: Sep 14, 2011
 

Background

Mild degrees of cognitive impairment, particularly when self-reported by patients, pose a substantial challenge to the clinician. The physician may be dealing with a patient with a mild or transient condition, a drug-induced adverse effect, or a depressive disorder; the patient may be in the early stages of a condition that will eventually lead to a dementia; or the complaint may be due to a psychological condition rather than an organic brain disorder. Because a variety of conditions may result in a complaint of cognitive impairment, an individualized workup for such conditions and a consensus on a therapeutic approach should be sought.

Normal expected age-related memory functions

  • Memory functions that remain relatively stable with increasing age
    • Semantic memory - Facts and general knowledge about the world; remains stable with age, especially if the information is used frequently[1] (However, retrieval of highly specific information, such as names, typically declines.)
    • Procedural memory – Acquisition and later performance of cognitive and motor skills[1]
  • Memory functions that decrease with age
    • Working memory - Holding and manipulating information in the mind such as reorganizing a short list of words into alphabetical order[1] ; verbal and visuospatial working speed, memory, and learning, with visuospatial cognition more affected by aging than verbal cognition[2]
    • Episodic memory – Personal events and experiences[1]
    • Processing speed[3]
    • Prospective memory – The ability to remember to perform an action in the future such as remembering an appointment or to take a medication[1]
    • Age-related decline in the ability to remember new text information, to make inferences about new text information, to access prior knowledge in long-term memory, and to integrate prior knowledge with new text information[4]
    • Declines in recollection[5]

To demonstrate that cognitive function is worse than expected for age, neuropsychological testing is necessary so that a patient’s performance can be compared with that of an age-matched (and ideally education-matched) control group.

Mild cognitive impairment (MCI) represents a stage of cognitive impairment that exceeds the normal expected age-related changes, but functional activities are largely preserved and so MCI does not meet the criteria for dementia.[6] Different subtypes of MCI are recognized. One common classification distinguishes between amnestic and nonamnestic forms of MCI. The amnestic form, where memory impairment predominates, is often a precursor for clinical Alzheimer’s disease. A variety of types of cognitive impairments may occur in nonamnestic forms of MCI, with the most common impairment probably being executive function. This form of nonamnestic MCI may be associated with cerebrovascular disease or may be a precursor for some frontotemporal dementias. A substantial number of patients with MCI may be judged as having normal cognition on follow-up visit.

Ultimately, long-term follow-up and eventual autopsy are necessary to distinguish between patients experiencing MCI due to preclinical Alzheimer’s disease and patients experiencing MCI due to less frequently occurring conditions. However, some factors can be helpful in predicting the likelihood of progression. The severity of memory impairment is predictive of progression to Alzheimer’s disease; those patients with more severe memory impairment are more likely to progress. Whole brain and hippocampal volume on MRI has been shown to be predictive of progression from MCI to Alzheimer disease[7] , as has apolipoprotein E (ApoE) status[8] ; however, ApoE testing is not recommended for routine clinical use.

No medications have been FDA approved for the treatment of MCI.

Previous attempts have been made to characterize cognitive decline associated with aging, including benign senescent forgetfulness, age-associated memory impairment, and age-associated cognitive decline.[9, 10, 11] The term MCI is intended to represent an intermediate stage between normal aging and the development of pathological aging and dementia (eg, the malignant senescent forgetfulness[10] ). Other terms with connotations similar to MCI include isolated memory impairment, incipient dementia, and dementia prodrome, although these latter terms are not nearly as widely accepted as MCI and they should not be considered as exact synonyms.

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Pathophysiology

The pathophysiology of MCI is multifactorial. Most cases of the amnestic form of MCI result from the pathological changes of Alzheimer disease that are not yet severe enough to cause clinical dementia.[12] At least in specialty research populations, autopsies in amnestic MCI have found the neuropathology to be typical of Alzheimer disease.[13] Nonamnestic MCI may be associated with cerebrovascular disease, frontotemporal dementias, or no specific pathology.

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Epidemiology

Frequency

United States

Annual prevalence estimates for MCI range from 3-4% in the eighth decade[14] in the general population and 19.2% for ages 65-74 years, 27.6% for ages 75-84 years, and 38% for ages 85 years and older[15] among community-dwelling African Americans.

Mortality/Morbidity

Subtypes of MCI progress to Alzheimer disease at different rates. A study by Roundtree et al showed that the conversion rate to Alzheimer disease for amnestic MCI was 56%, for amnestic-subthreshold MCI was 50%, and for nonamnestic MCI was 52%.[16] For all MCI subtypes, the 4-year conversion to dementia was 56% (14% annually) and to Alzheimer disease was 46% (11% annually).[16] This was compared with healthy elderly individuals who develop Alzheimer disease at a rate of 1-2% per year. Boyle et al reported that patients with MCI are almost 7 times more likely to develop Alzheimer disease compared with older individuals without cognitive impairment.[17] Of patients with MCI, 80% are said to progress to dementia after approximately 6 years. This is significant from the perspective that Alzheimer disease is often cast as the fourth leading cause of death in the United States.

At least one well-designed study has shown MCI as identified by the Short Portable Mental Status Questionnaire to be an independent predictor of mortality.[18] Wilson et al reported that in both African American and white patients, the risk of death was increased by about 50% among individuals with MCI and was nearly 3 times higher among those with Alzheimer disease.[19]

Race

Virtually nothing is known about cultural and racial factors influencing the clinical manifestations of MCI.

Sex

Many studies indicate that the risk of Alzheimer disease is significantly higher in women than in men, and it is therefore presumed that the likelihood of developing MCI is greater in women than in men.

Age

The prevalence of mild cognitive impairment increases with age. The prevalence is 10% in those aged 70-79 years and 25% in those aged 80-89 years.[20]

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Contributor Information and Disclosures
Author

Heather S Anderson, MD  Assistant Professor, Staff Neurologist, Department of Neurology, Alzheimer and Memory Center, University of Kansas Medical Center

Heather S Anderson, MD is a member of the following medical societies: American Academy of Neurology

Disclosure: Nothing to disclose.

Specialty Editor Board

Joseph Quinn, MD  Assistant Professor, Department of Neurology, Portland VA Medical Center, Oregon Health Sciences University

Joseph Quinn, MD is a member of the following medical societies: American Academy of Neurology, Society for Neuroscience, and Society for Pediatric Radiology

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Richard J Caselli, MD  Professor, Department of Neurology, Mayo Medical School, Rochester, MN; Chair, Department of Neurology, Mayo Clinic of Scottsdale

Richard J Caselli, MD is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, American Medical Association, American Neurological Association, and Sigma Xi

Disclosure: Nothing to disclose.

Selim R Benbadis, MD  Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, Tampa General Hospital, University of South Florida College of Medicine

Selim R Benbadis, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, and American Medical Association

Disclosure: UCB Pharma Honoraria Speaking, consulting; Lundbeck Honoraria Speaking, consulting; Cyberonics Honoraria Speaking, consulting; Glaxo Smith Kline Honoraria Speaking, consulting; Pfizer Honoraria Speaking, consulting; Sleepmed/DigiTrace Honoraria Speaking, consulting

Chief Editor

Michael Hoffmann, MBBCh, MD, FCP(SA), FAAN, FAHA  Professor of Neurology, University of Central Florida College of Medicine; Director of Cognitive Neurology, Director of Stroke Program, James A Haley Veterans Affairs Hospital

Michael Hoffmann, MBBCh, MD, FCP(SA), FAAN, FAHA is a member of the following medical societies: American Academy of Neurology, American Headache Society, American Heart Association, and American Society of Neuroimaging

Disclosure: Nothing to disclose.

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