Data for this review were identified by searches of PubMed and references from relevant articles published in English; additional articles were identified through searches of author's files. Search terms included “mild cognitive impairment”, “memory impairment”, and “cognitive impairment, not demented”.
ReviewMild cognitive impairment: prevalence, prognosis, aetiology, and treatment
Section snippets
Definitions of MCI
Several excellent reviews on the definition of MCI have recently been published15, 16 and the interested reader is referred to these for a more detailed overview of the subject. The idea of ageing-effects versus disease is not new; in 1962, Kral18 introduced the notion of “benign” versus “malignant” senescent forgetfulness to recognise differences between stable memory complaints of elderly people and those that potentially indicate early disease.18 Recognition that dementia can have a long
Estimates of prevalence
Formal studies of the prevalence of memory complaints within the community vary greatly, from 22% to 56%. Much of the variation relates to the average age of the population studied and the type of questions asked, but other factors such as sex and educational achievement appear important as well. For example, women and individuals with low educational achievement have a greater frequency of memory complaints.25 The high prevalence of complaints about memory problems from elderly people may
Pathophysiology of MCI
Many diseases can lead to cognitive impairment in the absence of dementia, particularly when cognitive impairment is defined as CIND (figure 4).5 Even within more restrictive definitions such as amnestic MCI, however, there appears to be sufficient heterogeneity to cause potential confusion with regard to prognosis and treatment.17 A review of the available evidence supporting the presence of both AD and cerebrovascular disease among individuals classified as having MCI is, therefore, necessary.
Longitudinal observation studies
Although individuals who complain of memory impairment may have variable rates of progression to dementia,25 any evidence of documented memory impairment, including age-associated memory impairment, increases the likelihood of future dementia.13, 24 This link may, however, reflect inclusion of subgroups of people who are both cognitively and genetically more similar to individuals with amnestic MCI.61
Most studies have directly examined the progression of amnestic MCI to dementia within the
Treatment
Recognition of MCI or CIND as transition phases between healthy ageing and dementia serves as an important tool for investigation of treatments aimed at secondary prevention of dementia.14 As emphasised earlier, however, treatment of the various forms of cognitive impairment among elderly people requires identification of the specific aetiology for the cognitive disorder to effect appropriate strategies. Current trials are focused on carefully selected populations at high risk of AD and
Conclusions
This review began by defining cognitive impairment syndromes among elderly people into two useful classifications—those that emphasise memory impairment and probably represent incipient AD, and those that are more broadly inclusive and encompass definitions that include non-memory cognitive impairments. The importance of making such distinctions stems from the recognition that cognitive impairment syndromes may result from various causes that reflect both clinical and pathological heterogeneity
Search strategy and selection criteria
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