Value of diagnostic tests to predict conversion to Alzheimer's disease in young and old patients with amnestic mild cognitive impairment

Using the database of the Alzheimer's Disease Neuroimaging Initiative, we examined the value of neuropsychological assessment, structural magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) biomarkers, and FDG-PET scanning with respect to prediction of conversion from mild cognitive impairment (MCI) to Alzheimer's disease (AD). We tested the hypothesis that CSF biomarkers and FDG-PET would lose prognostic value when applied in patients older than 75 years, whereas MRI and neuropsychological testing would not. At baseline 175 patients had MCI, mostly amnestic. They were followed during a mean of 2.7 years, and 81 patients converted to AD after a mean of 1.6 years. Logistic regression analyses showed that neuropsychological assessment and MRI variables predicted conversion with 63 to 67% classification success both in patients younger and older than 75 years, while CSF biomarkers attained this success rate only in patients younger than 75 years. For FDG-PET, this rate was 57% in the total sample. We conclude that the diagnostic yield of different techniques in predicting conversion from MCI to AD is moderate, and that it is affected by age of the subject under study. MRI and neuropsychological assessment remain informative in patients older than 75 years, unlike CSF biomarkers.