Neuropsychological Predictors of Time to Conversion from Mild Cognitive Impairment to Alzheimer's Disease

Mild Cognitive Impairment (MCI) is a risk state for the development of Alzheimer's disease (AD), though individual outcomes vary. Accurately predicting which MCI patients are likely to develop AD and how long they have until the onset of dementia could provide both patients and their families sufficient time to prepare. Neuropsychological tests have the advantage of objectively quantifying cognitive impairments, and may be useful in predicting time to conversion. The present project aimed to 1) compile the available literature concerning neuropsychological predictors of conversion from MCI to AD using systematic review and meta-analytic techniques and 2) to determine if neuropsychological profiles differentiate MCI patients who convert to AD sooner, those who convert later, and those who do not convert utilizing a statistical technique known as profile analysis. Findings from the systematic review illuminated several gaps in the literature such as the small number of studies that follow patients over longer periods of time. Results from the meta-analysis suggested that word recall and recognition tasks, complex figure recall tasks, simple shape recall tasks, Trail Making Task B (TMT-B), semantic fluency, and the Mini Mental State Examination (MMSE) differentiated between MCI patients who convert sooner (within three years) from those who maintain an MCI diagnosis over three years. Results from the second part of the project found that verbal memory measures best distinguished those who converted sooner from those who converter later. In comparison with those who convert within three years, the group that maintained an MCI diagnosis completed TMT-B more quickly and performed better on memory measures. Neuropsychological measures did not distinguish between those who maintained an MCI diagnosis and those who converted after three years. Taken together, results from the two studies suggest that clinicians may wish to rely upon memory measures and TMT-B performance when considering recommendations regarding length of follow-up and planning for the onset of dementia in patients with MCI. In order to better understand predictors of time to conversion from MCI to AD, future studies should follow participants over several years and make direct comparisons between those who convert sooner and those who convert later.