The Path from Mild Cognitive Decline to Dementia

Mild cognitive impairment (MCI) is a midpoint between normal cognitive function and Alzheimer’s disease.  In different studies and different populations, 4% to 15% of patients with MCI will convert to Alzheimer’s each year.  It would be important to know of any features that could help predict which patients would make the change.  A study published in the Archives of Neurology provides one such clue.

University of California-Davis scientists followed 111 individuals with MCI for an average of 2.4 years.  About 45% of them were recruited from a clinical setting and 55% were recruited directly through community outreach.  They all had annual clinical evaluations, diagnostic neuroscans (MRI), routine lab tests, and neuropsychological evaluations.  The Clinical Dementia Rating Scale was used to estimate the functional ability of the individual; the functional components of this are roughly equivalent to the Activities of Daily Living (ADL) scale. 

 During follow-up, 28 patients progressed to Alzheimer’s disease, with an average time to conversion of 2.19 years.  For those recruited form the clinic, the conversion rate was 13% per year, while the community sample converted at a rate of 3%.  Age, gender, and education were not related to this discrepancy between conversion rates. 

 More comprehensive analyses showed that the only factor linked with conversion from MCI to Alzheimer’s was the degree of functional impairment at the start of the study; this was derived from the relevant components of the Clinical Dementia Rating Scale.  This finding held true whether the patients were recruited from the clinic or the community.        

 The bottom line?  More functional impairment is an important risk factor for future conversion to dementia.