Correlation of brain structural and functional changes in amnestic mild cognitive impairment and mild Alzheimer's disease: A voxel-by-voxel analysis in a single cohort of patients in Brazil

Abstract

Amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD) are believed to be a continuum of the same process, in which aMCI is a symptomatic pre-dementia stage. There is a growing need to early diagnosis and neuroimaging methods may help it. Nevertheless, there is a relative lack of studies which correlate findings in magnetic resonance imaging (MRI) and functional imaging such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) in the same cohort of patients. The objective of this study was to compare the findings of these three methods in mild AD, aMCI and in normal elderly volunteers (control group - CG). We prospectively evaluated 94 subjects that were distributed after clinical and neuropsychological evaluation as follows: 34 in the mild AD group (CDR=1.0); 30 in the aMCI group (CDR = 0.5); and 30 in the CG (CDR= 0). All patients were submitted to MRI for volumetric based morphometry (VBM), brain perfusion SPECT with ECD- 99m Tc and glucose metabolism PET with 18 F-fluordeoxyglucose (FDG-PET). Results were quantified and compared in a voxel by voxel basis with the software SPM8. Patient clinical data are detailed in Table 1. In relation to CG, AD showed volumetric reductions in both temporal lobes (parahippocampal gyrus / amigdala and middle temporal gyrus), reduction in glucose metabolism bilaterally in parahippocampal uncus, temporoparietal regions and posterior cingulate. SPECT disclosed reduced perfusion in left parahippocampal gyrus, transverse temporal gyrus and right precuneus. The aMCI group showed only discrete changes including volume reduction in the left superior temporal gyrus, glucose hypometabolism in the right precuneus and flow reduction in the left superior temporal gyrus and transverse temporal gyrus. The findings of MRI, FDG-PET and SPECT were in part concordant, mostly in AD. Those have been previously reported and correspond to some of the imaging hallmarks of mild AD. PET showed higher extension of involvement in comparison to both MRI and SPECT, depicting a poor association between volumetric and functional abnormalities in AD. It was not possible to see a perfect concordance among the three technologies in aMCI, findings in contrast with other reports in the literature.