Serial PET + cognitive tests may help keep tabs on Alzheimer’s progression

Standard methods of evaluation for Alzheimer’s disease (AD) including cognitive tests and one-time PET imaging do not provide a bird’s eye view of disease development. A technique combining a range of examinations and a series of F-18 FDG PET studies is providing researchers valuable information about AD formation, according to research published July 12 in the Journal of Nuclear Medicine.

Sepideh Shokouhi, PhD, from the department of radiology and radiological sciences at Vanderbilt University Institute of Imaging Science in Nashville, Tenn., and colleagues conducted a retrospective study mining data from the Alzheimer Disease Neuroimaging Initiative to track longitudinal changes in the brains of patients and how they relate to cognitive decline. F-18 FDG PET was used to measure rates of cerebral glucose utilization as an indicator of neuronal function and synaptic density in the brains of AD patients and healthy controls.

“The longitudinal relationships between cognitive decline and metabolic function as assessed using F-18 FDG PET are needed to address both the cognitive and the biologic progression of disease state in individual subjects,” wrote Shokouhi et al.

Rather than focusing on uptake, researchers reviewed the spatial distribution of FDG across multiple imaging studies using a parameter titled the regional F-18 FDG time correlation coefficient (rFTC). They conducted an analysis using linear mixed-effects models to evaluate for dropping rFTC in high-risk patients. High risk was determined by the presence of risk factors such as APOE-4 allele or mild cognitive impairment. These data were correlated with the mental examination to determine relationships between rFTC and reduced cognitive ability. F-18 FDG imaging focused on a range of brain regions in order to pick up subtle changes in areas not usually highlighted in conventional AD imaging.

“Our study allows a direct and straightforward comparison between metabolic changes (F-18 FDG) and cognitive changes (ADAS_cog, FAQ, and MMSE) in the same subject,” wrote the authors. “Such patient-based comparison is potentially less sensitive to metabolic heterogeneities across subjects and might reveal interesting links between biologic and cognitive markers of the AD state.”

A total of 51 subjects, 24 healthy controls and 27 mildly cognitive impaired patients were included. Each was scanned four times within an average four-year period. Results showed that values of rFTC remained consistent in controls with 20.005 change per year, whereas cognitively impaired subjects demonstrated a more rapid decline and an added change of 20.02. This significant dip in rFTC was correlated with longitudinal cognitive decline.

“Longitudinal changes in rFTC detect subtle metabolic changes associated with variations in cognition,” wrote the researchers. “This analytic tool may be useful for monitoring cognitive decline in individual subjects.”