Mild Cognitive Impairment, Dementias, and Alzheimer’s Disease

Mild Cognitive Impairment, Dementias, and Alzheimer’s Disease

Vaunette P. Fay

Christine St. Michel


The term mild cognitive impairment (MCI) represents an intermediate stage of cognitive function between normal aging and development of pathologic aging and dementia.1 Most people undergo a minor gradual cognitive decline in regard to memory over their life span which has no impact on their ability to function. However, some people experience a decline in cognitive function beyond that which is associated with typical aging that impairs their ability to function normally, and is often recognized by those around them. MCI is receiving considerable attention in clinical practice and research settings.2 The affected individual may have memory, language, or other essential cognitive function impairment serious enough to be noticeable to others and to be documented on tests, but not severe enough to interfere with daily life. The diagnostic process for MCI is similar to Alzheimer’s disease (AD) since no diagnostic testing is available, and requires the judgment of a clinician. It is often difficult to differentiate MCI from normal aging or early dementia. Usually, in patients with dementia as the disease progresses, cognitive deficits affect daily function such that results in loss of independence in the community.

Neuropsychological testing is necessary so the patient’s performance can be compared with that of an age-match and ideally, education-matched control group.1 The following clinical criteria are used for the diagnosis of MCI.

  • Concern regarding a change in condition different from patient’s baseline

  • Impairment in one or more cognitive domains, that is, memory, executive function, language, visiospatial skills, episodic memory

  • Preservation of independence in functional abilities

  • No evidence of impairment in social or occupational functioning

Memory is the most common domain involved in patients who progress to AD. Some, but not all, people with MCI develop dementia over time, especially when their primary area of difficulty involves memory.3, 4 The differentiation of dementia from MCI is based on the determination of whether or not significant interference in the ability to function at work or in usual daily activities exists.5 Health care providers should be careful not to label patients affected with MCI as having early Alzheimer’s, since the patient’s precise outcome is not certain.2


The pathophysiology of MCI is multifactorial but most cases result from pathologic changes of AD that have not reached the severity to result in clinical dementia.1 Autopsies conducted on patients with MCI revealed neuropathology typical of AD. Two subtypes of MCI pathology result. Amnestic MCI often results from AD pathology and most patients with amnestic MCI progress to clinical AD within 6 years. Nonamnestic forms of MCI may be due to multiple factors such as cerebrovascular disease, Parkinson’s disease (PD),

Lewy body dementia, or no specific underlying pathology.1


The prevalence of MCI increases with age. The estimated annual prevalence for MCI in the United States ranges from 3% to 4% for those over age 80 in the general population. The estimated prevalence among community-dwelling African Americans has increased to 10.2% for ages 65 to 74, 27.6% for ages 75 to 84, and 38% for those of ages 85 years and older. Not much is known about cultural and racial factors that influence the clinical manifestations of MCI. Approximately 10% to 15% of individuals diagnosed with MCI convert to AD per year, resulting in a 5-year conversion rate of 50% to 70%.6, 7 Since the diagnostic workup of MCI is similar to that of dementia, please refer to the section under dementia workup.


Dementia is the generic term for a group of disorders that cause irreversible cognitive decline as a result of various pathologic mechanisms that damage brain cells. It is estimated that 3% to 11% of people over the age of 65 have dementia, and increasing incidence, up to 47%, in those aged 85 years and older. Approximately 50% to 75% of those people have AD. The incidence of AD and vascular dementia (VaD) is age related; that is, the older one has the greater chance of having either disease.6 Considering the demographic projections for the increased number of older people in the United States, the number of cases of dementia is expected to increase to 18.5 million by 2050, with an estimated annual cost of $172 billion.8

Health providers must be prepared for the needs of this expanding population.

Definitions of dementia vary and are usually derived from the Diagnostic and Statistical Manual of Mental Disorders (4th ed., text revision), known as DSM-IV-TR, and the International Classification of Diseases (10th revision), known as ICD-10.9 Currently, to be classified as a type of dementia, the following two criteria are used.10, 11

  • Decline in memory and at least one of the four following cognitive functions.

    • Ability to generate coherent speech or understand spoken or written language

    • Capacity to plan, makes sound judgments, think abstractly, and carry out complex tasks

    • Ability to execute motor activities assuming intact motor ability

    • Ability to process and interpret visual information

  • Decline is severe enough to interfere with day-to-day life.

The Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV),9 defines dementia as “the development of multiple cognitive deficits that include memory impairment and at least one of the following: aphasia, apraxia, agnosia, or a disturbance in executive functioning. These deficits must be sufficiently severe to cause impairment in occupational or social functioning, and must represent a decline from a previously higher level of functioning.”5 Recommended changes to the criteria for the next revision of the DSM-IV include recognition of the acquired nature, progressive loss of functional capacity, and frequent personality and behavior changes.12

The causes of dementia are numerous (Table 30-1) and vary by age group. AD, the major cause of dementia accounting for more than half of all dementias (50% to 70%), is followed by VaD (20% to 25%).13 A classification of dementia is found in Table 30-2. It lists the major categories of dementia including AD, VaD, mixed dementia, PD with dementia, dementia with Lewy bodies, frontotemporal dementia, and normal pressure hydrocephalus dementia. There has been increased interest in Lewy body causes of dementia. A Lewy body is an intracytoplasmic eosinophilic neuronal body surrounded by a lighter halo seen in some neurodegenerative disease. In PD, Lewy bodies are found in neurons of the degenerating substantia nigra. Lewy bodies can also be found in lesser numbers in other central nervous system (CNS) degenerative conditions, and occasionally in the brains of nonparkinsonian elderly persons.14 Type 2 diabetes mellitus has been linked to accelerated cognitive decline in older adults, development of MCI, and increased risk for dementia.

Some dementias are associated with an underlying primary condition and may be reversible with prompt treatment; these dementias are referred to as the reversible dementias. The most important challenge in treating dementia is identifying cases, some of which are uncommon, of reversible dementia such as chronic drug intoxication, vitamin deficiencies (e.g., B12 and foliate), subdural hematoma, major depression, normal pressure hydrocephalus, and hypothyroidism.2 In other instances, dementia is a chronic, irreversible condition, resulting in progressive loss of overall cognitive function. Although the dementia is not curable, it does not mean that symptoms cannot be managed and treated. The symptoms that are treatable include behavioral disorders, sleep disorders, and depression. Some drug therapy is alleged to slow the progression of the neurodegenerative process.


Major Causes of Dementia in U.S. Population

  • Alzheimer’s disease (>50%) of all cases

  • Vascular dementia (20-25%): also called multi-infarct dementia and poststroke dementia

  • Lewy body disease (15-25%)

  • Alcoholism

  • Parkinson’s disease (about 25% of patients with Parkinson’s develop dementia)

  • Drug/medication toxicity (potentially reversible)a

Other Less Common Causes of Dementia

Degenerative disorders

Pick’s disease; Huntington’s disease; cortical basal degeneration; MS; some forms of ALS and PD; and other disorders

Chronic infections

HIV, Creutzfeldt-Jakob disease, PML, neurosyphilis,a and opportunistic infections (TB, fungal, protozoal);a sarcoidosisa


Primary and metastatic brain tumors


Heavy metals;a organic toxins

Vitamin deficienciesaa

Thiamine [B1]-Wernicke’s encephalopathy; vitamin B12 pernicious anemia

Endocrine and other system diseasesa

Hypothyroidism; parathyroidism; adrenal insufficiency, and renal, liver, or pulmonary failures

Head trauma and diffuse brain damage

Chronic subdural hematoma;a normal pressure hydrocephalus;a hypoxic brain syndrome; postencephalitis

Psychiatric disordersa

Depression; conversion reaction

a Potentially reversible dementia either by category or specific problem. ALS, amyotrophic lateral sclerosis; MS, multiple sclerosis; PD, Parkinson’s disease; PML, progressive multifocal leukoencephalopathy; TB, Mycobacterium tuberculosis.

Jul 14, 2016 | Posted by in NURSING | Comments Off on Mild Cognitive Impairment, Dementias, and Alzheimer’s Disease

Full access? Get Clinical Tree

Get Clinical Tree app for offline access