11C]PiB in patients with amnestic and non-amnestic MCI

Abstract

The ability to quantify amyloid deposition using in vivo neuroimaging labeling compounds, such as the Pittsburgh Compound B [11C]PiB for amyloid holds the promise of confirming the diagnosis of Alzheimer's disease (AD) prior to autopsy. The use of [11C]PiB to identify pre-clinical AD (i.e., in patients with Mild Cognitive Impairment; MCI) may prove beneficial as this would allow interventions to be targeted earlier when the response to intervention is potentially greater. To date, however, few studies have compared diagnostic subcategories of MCI using [11C]PiB. Twenty two older individuals (range 61-93 years) diagnosed with MCI enrolled in the Michigan Alzheimer's Disease Research Center underwent [11C]PiB positron emission tomogrophy (PET) scan. Patients were divided into [11C]PiB “positive” or [11C]PiB “negative” groups: [11C]PiB positive individuals demonstrated frontal cortical binding in excess of subcortical white matter binding. In addition, all individuals were administered a battery of neuropsychological tests that included measures from the NACC Uniform Data Set. Fourteen of the 22 patients were positive for abnormal [11C]PiB binding. Of those 14, 13 of the patients had MCI amnestic type (8 memory alone, 5 memory plus additional cognitive impairment). Of the 8 who were negative for [11C]PiB, only 3 presented as MCI amnestic type, with 5 diagnosed as MCI nonamnestic (χ2=7.9, p<.005). The [11C]PiB positive group demonstrated poorer performance on measures of visual memory (immediate memory p<0.04, delayed recall p<0.03) and verbal recognition (p<0.05). No differences were found in other cognitive domains, though a trend was evident for more executive functioning impairment in the [11C]PiB negative group (p<.09). Amyloid deposition in patients with diagnosed MCI is more prevalent in patients who present with memory deficits. As previous research has suggested that patients with MCI amnestic type are at a higher risk of developing Alzheimer's disease (AD), the use of [11C]PiB scans may help in the identification of those individuals who are at greatest risk for AD. Supported by NIH-NIA P50 AG08671 and the Michigan Alzheimer's Disease Research Center.