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In elderly people with mild cognitive impairment (MCI), what is the long-term rate of conversion to dementia?
Included studies examined the progression of MCI, defined according to accepted criteria. Outcomes were dementia or probable Alzheimer disease (AD).
Medline, EMBASE/Excerpta Medica, and PsycINFO (to Mar 2008) were searched for cohort studies that had ⩾5 years of follow-up. 15 studies (n = 2402, mean age 62–82 y) met the selection criteria. Mean follow-up was 6 years (range 5–10 y).
The cumulative conversion rate to dementia was 31% (15 studies) and to AD was 33% (11 studies). The table shows annual conversion rates. Annual conversion rates were lower in studies with longer duration of follow-up.
In elderly people with mild cognitive impairment who were followed up for ⩽10 years, the annual conversion rate to dementia was 3.3%.
A modified version of this abstract appears in ACP Journal Club in Ann Intern Med and Evidence Based Medicine.
Mitchell AJ, Shiri-Feshki M. Temporal trends in the long term risk of progression of mild cognitive impairment: a pooled analysis. J Neurol Neurosurg Psychiatry 2008;79:1386–91.
Clinical impact ratings: Elderly care 7/7; Family/general practice 5/7; Neurology 5/7
Given the ageing population and the corresponding increase in people diagnosed with dementia and AD, an improved understanding of the possible trajectories of MCI can help healthcare providers in community and long-term care settings meet the needs of patients and their families living with these diagnoses.
Previous research had suggested a higher annual rate of conversion from MCI to AD and dementia. The well-designed review by Mitchell and Shiri-Feshki examined studies with longer observational periods, challenging us to rethink our understanding of annual conversion rates, overall rates of conversion to AD and dementia, and our treatment approaches.1 After reviewing data from 15 studies, the authors suggested that the projection of MCI needs further examination. This conclusion is in keeping with those of recent articles looking at the relatively new diagnosis of MCI.2 ,3 One possible reason for the lower annual conversion rates found in this review is that the MCI groups may have been more heterogeneous, with the possibility of misdiagnosis, especially if patients were not followed up with subsequent assessments; the MCI cohorts may, in fact, have included people with disorders that remained stable or improved.
A key implication for practice from the review by Mitchell and Shiri-Feshki is that nurses and nurse practitioners working in the community may need to modify the message they give to individuals and families when MCI is diagnosed. They need to be cautious and emphasise that MCI does not always convert to dementia; thus, accurate diagnosis of dementia is critical because different types of dementia likely require different treatment approaches.1 The review also highlights the need for ongoing assessment of an individual’s cognition, abilities, and emotional and social responses to cognitive changes. It is only as cognitive processes change (or do not) that clinicians will have a clearer picture of how to help individuals and their families.
Source of funding: no external funding.
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