The high annual conversion rate of 10-15% for MCI progression appears to be limited to short-term observation of clinical samples, with rates decreasing over long-term follow-up.
A 10-15% ACR only appears to hold true in clinical samples monitored over a short observation period. Recruitment of older individuals from specialist centres, particularly involving those who complain of cognitive difficulties (subjective memory complaints) will tend to favour high conversion rates. In the first few years of follow-up, many of those with the most adverse risk profile will tend to progress, dropout or die, leaving a cohort of less vulnerable sufferers. However, an inverse temporal relationship was also manifest in those who completed long term follow-up, suggesting other factors are involved such as sampling issues or heterogeneity in MCI itself.
Mitchell et al. (Fri,) studied this question.