MILD COGNITIVE IMPAIRMENT
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
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
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
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.
TABLE 30-1 COMMON CAUSES OF DEMENTIA
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%)
Parkinson’s disease (about 25% of patients with Parkinson’s develop dementia)
Drug/medication toxicity (potentially reversible)a
Other Less Common Causes of Dementia
Pick’s disease; Huntington’s disease; cortical basal degeneration; MS; some forms of ALS and PD; and other disorders
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
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
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.