Conversion of amyloid positive and negative MCI to AD over 3 years An 11C-PIB PET study

Background: Patients with amnestic mild cognitive impairment (MCI) represent an important clinical group as they are at increased risk of developing Alzheimer disease (AD). C-11-PIB PET is an in vivo marker of brain amyloid load. Objective: To assess the rates of conversion of MCI to AD during a 3-year follow-up period and to compare levels of amyloid deposition between MCI converters and nonconverters. Methods: Thirty-one subjects with MCI with baseline C-11-PIB PET, MRI, and neuropsychometry have been clinically followed up for 1 to 3 years (2.68 +/- 0.6 years). Raised cortical C-11-PIB binding in subjects with MCI was detected with region of interest analysis and statistical parametric mapping. Results: Seventeen of 31 (55%) subjects with MCI had increased C-11-PIB retention at baseline and 14 of these 17 (82%) clinically converted to AD during follow-up. Only one of the 14 PIB-negative MCI cases converted to AD. Of the PIB-positive subjects with MCI, half (47%) converted to AD within 1 year of baseline PIB PET, these faster converters having higher tracer-retention values than slower converters in the anterior cingulate (p = 0.027) and frontal cortex (p = 0.031). Seven of 17 (41%) subjects with MCI with known APOE status were epsilon 4 allele carriers, this genotype being associated with faster conversion rates in PIB-positive subjects with MCI (p = 0.035). Conclusions: PIB-positive subjects with mild cognitive impairment (MCI) are significantly more likely to convert to AD than PIB-negative patients, faster converters having higher PIB retention levels at baseline than slower converters. In vivo detection of amyloid deposition in MCI with PIB PET provides useful prognostic information. Neurology (R) 2009;73:754-760