The featured paper is ‘Frequency and Course of Mild Cognitive Impairment in a Multiethnic Community’ by Manly and colleagues and freely available here.
This is a longitudinal study looking at 2364 people of different ethnicity over the age of 65 over a period of up to 24 months. The subjects were recruited from New York and received Medicare and being broadly classed into Caribbean Hispanic, African American and ‘non-Hispanic White of European Ancestry’. The methodology is complicated as the researchers used data from two longitudinal studies with follow-up periods of 30 months these two periods occurring some 7 years apart from each other. However it’s not clear that this compromised the study findings other than to say that at the Leon Thal Symposium 2008, a number of prominent researchers noted that memory decline seemed to decrease in the placebo arms of trials with each passing decade (although this might be due to the characteristics of placebo arms of trials). There were a number of people lost to follow-up either due to death or other reasons. Additionally data was not forthcoming for some of the others included in the trial. Of those that died, the group had more years in education but otherwise did not differ significantly from the remainder of the cohort. Additionally post-mortems were conducted.
Peterson’s Criteria for Mild Cognitive Impairment were used.
The authors found that
1. The mean age of the sample was 71 years of age with a standard deviation of 6.2 years
2. 21% of the sample without impairment developed MCI (95% CI – 4.6%-5.6%). In those where APOE-e4 status was available there wasn’t found to be a higher risk of developing MCI. Hypertension was risk factor for developing MCI (RR 1.4 95% CI 1.1-1.9).
3. 21.8% with MCI developed Alzheimer’s Disease with an annual incidence rate of 5.4% (95% CI -4.7%-6.3%). Memory impairment on the composite score was a predictor of progression to Alzheimer’s Disease in subjects with MCI (RR 3, 95% CI 2.32-3.86).
4. Diabetes, stroke, African-American and Hispanic ethnicity were associated with a higher risk of progression to Alzheimer’s Disease. People with less than 12 years of school were twice as likely as those with more than 12 years of school to develop Alzheimer’s Disease. The authors later comment in the discussion thatin the African-American and Hispanic groups, there wasn’t any increased risk of MCI and added that this was because an ethnicity appropriate assessment was used in these groups. As there was no comment on the Alzheimer’s Disease findings the authors presumably imply that ethnicity specific assessments were required as otherwise they would need to explain the findings.
5. Just under half of those with MCI continued to experienced MCI – 47%
6. 31% of those with MCI had ‘reverted to normal’ at the end of the study period. In this group, reversion most frequently occurred because subjects no longer met cognitive criteria.
7. Memory and language difficulties predicted development of Alzheimer’s Disease
8. Impairment in more than one cognitive domain increased the likelihood of progression to Alzheimer’s Disease
Roughly speaking therefore, there was a rule of 20’s, 20% developing MCI and 20% of MCI developing Alzheimer’s Disease over the 2-year follow-up period.
This is a complex epidemiological study with many interesting findings.
Steps to Treatment = 4 (The findings here can be used to develop incidence/prevalence models. However the authors caution that further studies are required before generalisations can be made)
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