Elsevier

The Lancet

Volume 367, Issue 9518, 15–21 April 2006, Pages 1262-1270
The Lancet

Seminar
Mild cognitive impairment

https://doi.org/10.1016/S0140-6736(06)68542-5Get rights and content

Summary

Mild cognitive impairment is a syndrome defined as cognitive decline greater than expected for an individual's age and education level but that does not interfere notably with activities of daily life. Prevalence in population-based epidemiological studies ranges from 3% to 19% in adults older than 65 years. Some people with mild cognitive impairment seem to remain stable or return to normal over time, but more than half progress to dementia within 5 years. Mild cognitive impairment can thus be regarded as a risk state for dementia, and its identification could lead to secondary prevention by controlling risk factors such as systolic hypertension. The amnestic subtype of mild cognitive impairment has a high risk of progression to Alzheimer's disease, and it could constitute a prodromal stage of this disorder. Other definitions and subtypes of mild cognitive impairment need to be studied as potential prodromes of Alzheimer's disease and other types of dementia.

Section snippets

Background and conceptual development

Many attempts have been made to define the clinical entity of declining cognitive abilities associated with ageing. In the early part of the 19th century, Prichard1 identified the earliest stage of dementia as impairment of recent memories with intact remote memories. More than a century later, Kral2 espoused a contrasting viewpoint, with his description of benign senescent forgetfulness, in which fairly unimportant data and parts of an experience are not recalled and in which the forgotten

Pathophysiology

Much clinical evidence exists for the detrimental effects of anticholinergic drugs on cognition.19 A central cholinergic deficit is thought to be present in amnestic mild cognitive impairment, related to loss of neurons in the nucleus basalis of Meynert,20 although findings of a post-mortem study showed upregulation of choline acetyltransferase activity in the frontal cortex and hippocampus.21 This upregulation could be a compensatory mechanism, which is suggested by recruitment of memory and

Diagnosis

In terms of research diagnostic criteria, there is uncertainty about whether a lumping-together approach to mild cognitive impairment33 is preferable to a splitting approach, with various categories of the disorder.34 Prospective cohort studies are underway to establish whether amnestic and non-amnestic subtypes of mild cognitive impairment (figure)35 have different prognoses for progression to dementia and which type of dementia they predict35 and their effect on survival times.36 It is

Management

The first wave of clinical trials aimed at symptomatic drug treatment for amnestic mild cognitive impairment over 6 months to 3 years have been largely unsuccessful.76 Results from the Memory Impairment Study16 showed no significant differences in the probability of progression from amnestic mild cognitive impairment to Alzheimer's disease in patients allocated vitamin E or donepezil, compared with placebo, during the 3 years of treatment, although significant differences were recorded

Prevention

Although no specific disease-modifying treatment has yet been shown to be effective for any of the degenerative dementias, control of risk factors might prove useful. The best evidence available so far is in the control of isolated systolic hypertension.23 The idea of interventional epidemiology proposed by Ritchie13 for mild cognitive impairment will probably lead to international randomised controlled trials linking the consortia of investigators interested in the causes and treatment of mild

Conclusions

The syndrome of mild cognitive impairment as a transition state between normal ageing and dementia has increased awareness that memory complaints in elderly people, particularly when accompanied by subtle cognitive performance difficulties, should be assessed in a systematic way by clinicians. Prospective cohort studies with clinicopathological correlations will help to clarify whether some of the subtypes of mild cognitive impairment are prodromal stages of specific dementias, paving the way

Search strategy and selection criteria

This Seminar is based on discussions that took place during an Expert Conference sponsored by the International Psychogeriatric Association. Presenters were asked to review published work relevant to their assigned topics and to summarise the available evidence, areas of agreement, areas of uncertainty, and research priorities. This was not a consensus conference, but rather an opportunity to review available data and offer an expert opinion on where mild cognitive impairment stands as a

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