Mild cognitive impairment: Hope for stability, plan for progression
ABSTRACTMild cognitive impairment (MCI) is a common heterogeneous syndrome that in some cases is transitional between normal age-related cognitive changes and dementia. Identifying it early may lead to prompt recognition of reversible causes and allows for timely future planning. This article describes definitions of MCI and its evaluation, differential diagnosis, and management.
KEY POINTS
- MCI that primarily involves memory or multiple domains has a higher risk of progressing to dementia.
- Depression and the effects of anticholinergic medication can mimic MCI, and these should be looked for in patients presenting with cognitive loss.
- Impaired functional status as reflected in activities of daily living is an important sign of progression from MCI to dementia.
- Acetylcholinesterase inhibitors are not approved for treating MCI, have shown little efficacy in altering progression to dementia, and have multiple side effects.
- Enhancing physical and mental health and developing strategies to compensate for deficits are key management approaches.
As our population ages, people are thinking more about preserving their quality of life, especially with regard to maintaining their cognitive and functional abilities. Older patients and caregivers often raise concerns about cognitive issues to their primary care providers: many patients have memory complaints, are worried about whether these are merely part of normal aging or symptoms of early dementia, and want strategies to forestall the progression of cognitive impairment.
Mild cognitive impairment (MCI) is a heterogeneous syndrome that in some cases represents a transition between normal aging and dementia. However, this condition is not yet well understood. Although some patients progress to dementia, others remain stable, or even improve. This article will review the current definitions and the underlying physiology of MCI, as well as diagnostic and management strategies.
COGNITIVE CHANGES OCCUR WITH NORMAL AGING
Cognition is defined as a means of acquiring and processing information about ourselves and our world. It includes memory as well as other domains such as attention, visuospatial skills, mental processing speed, language, and executive function. Cognitive abilities typically peak between ages 30 and 40, plateau in our 50s and 60s, and decline in our late 70s.
With age come detectable changes in the brain: brain weight declines by 10% by age 80, blood flow diminishes, neurons are lost throughout life, and nerve conduction slows. Despite these changes, the brain has a great deal of functional reserve capacity.
Table 1 compares the signs of normal aging, MCI, and dementia. Normally, cognitive abilities decline gradually with age without affecting overall function or activities of daily living. Even in normal aging, the processing of new information (new learning) is reduced. Mental processing becomes less efficient and slower. Visuospatial skills gradually decline, recall slows, and ultimately, the speed of performance slows as well. Additionally, distractibility increases. On the other hand, normal aging does not affect recognition, intelligence, or long-term memory.1
The line between the normal effects of aging on cognition and true pathologic cognitive decline is blurry. In a busy clinical practice, it is often difficult to determine whether problems with memory and cognition that elderly patients and their family members describe represent true pathologic decline. In general, the clinical presentation of MCI is more profound than that of age-associated cognitive impairment: whereas normal aging may involve forgetting names and words and misplacing things, MCI frequently involves forgetting conversations, information that one would ordinarily remember, appointments, and planned events.
BETWEEN NORMAL AGING AND DEMENTIA
MCI is a transitional state between normal cognition and dementia. But the course is not inevitably downward: on follow-up, patients with MCI may be better, stable, or worse (see PROGNOSIS VARIES, below).
On autopsy studies, the brains of people with MCI appear intermediate between normal brains and brains of people with Alzheimer-type dementia, which have neurofibrillary tangles, amyloid senile plaques, and neuronal degeneration.
Definitions of MCI vary
True cognitive decline that is more profound than normal aging was named and defined differently in different studies, making comparisons difficult. The concept of MCI arose from the term “benign senescent forgetfulness,” used by Kral in 1962.2 Other early terms include “cognitive impairment no dementia,” “memory impairment,” “mild cognitive disorder,” and “mild neurocognitive disorder.”3,4
MCI was first defined as a precursor to Alzheimer dementia. The term later described a sometimes reversible but abnormal state. It is a heterogeneous syndrome in terms of etiology, incidence, prevalence, presentation, and overall prognosis.
Most recently, MCI has been defined as5,6:
- Subjective memory complaints, preferably qualified by another person
- Memory impairment, with consideration for age and education
- Preserved general cognitive function
- Intact activities of daily living
- Absence of overt dementia.
MCI may arise from vascular, neurodegenerative, traumatic, metabolic, psychiatric, and other underlying medical disorders.7–9
The prevalence of MCI is difficult to determine because of the various definitions, populations studied (eg, clinic-based vs community-dwelling), and evaluation techniques. Published rates vary from 2% to 4% in all patients to 10% to 20% in the elderly. Incidence rates in the elderly vary from 14 to 75 per 1,000 patient-years.10–14
