Incidence and outcome of mild cognitive impairment in a population-based prospective cohort

TLDR

MCI is defined as memory complaints with objective memory impairment, without dementia, general cognitive dysfunction, or disability in activities of daily living. The study aimed to estimate age‑specific incidence rates of MCI by sex and education and to examine its course, particularly progression to Alzheimer’s disease, in a population‑based cohort followed for five years. Incidence rates were calculated using the person‑years method, and a descriptive analysis of follow‑up data was performed to assess the course of MCI in the cohort of nondemented elderly. During five years, 40 incident MCI cases occurred among 1,265 at‑risk subjects, giving an incidence rate of 9.9 per 1,000 person‑years; MCI predicted conversion to Alzheimer’s disease with an 8.3% annual rate and good specificity, yet only 6% remained MCI after 2–3 years while over 40% reverted to normal, highlighting its instability and suggesting the definition may be too restrictive.

Abstract

To estimate the age-specific incidence rate of mild cognitive impairment (MCI) according to sex and educational level and to explore the course of MCI, particularly its progression to AD, in a population-based cohort.A community-based cohort of nondemented elderly people (Personnes Agées QUID [PAQUID]) was followed longitudinally for 5 years. MCI was defined as memory complaints with objective memory impairment, without dementia, impairment of general cognitive functioning, or disability in activities of daily living. Incidence rates were calculated using the person-years method. A descriptive analysis at the different follow-up times was performed to study the course of MCI.At baseline, there were 58 prevalent cases of MCI (2.8% of the sample). During a 5-year follow-up, 40 incident cases of MCI occurred in 1,265 subjects at risk. The global incidence rate of MCI was 9.9/1,000 person-years. MCI was a good predictor of AD with an annual conversion rate of 8.3% and a good specificity, but it was very unstable over time: Within 2 to 3 years, only 6% of the subjects continued to have MCI, whereas >40% reverted to normal.Conventionally defined MCI has reasonable predictive value and specificity for AD. However, MCI was very unstable across time in this study. Furthermore, the definition of MCI seems to be too restrictive and should probably be extended to other categories of individuals also at high risk of developing AD.