Classification of early and severe Alzheimer Disease. Differences in accuracy basing the analysis of SPECT CBF data on either hippocampus, temporo-parietal lobes or factorial analysis

Background: Hippocampus and temporo-parietal regional cerebral blood flow (rCBF) reductions are well known to be specific of early (eAD) and severe Alzheimer Disease (AD). The specificity and the sensitivity of SPECT rCBF in discriminating the two stages of the disease vary across different investigations. The aim of this study is to develop a new method to increase the accuracy in the classification of eAD and AD. Methods: Twenty eAD and 21 controls (CTR), and 15 AD and 13 further CTR were included in the study. The two group pairs were age-matched and rCBF was assessed by 99m-Tc-HMPAO and using a three-headed gamma camera. Regions were identified and signal intensity was evaluated by a standardised brain atlas. Hippocampus, temporal and parietal lobes and four factors, derived from a previous principal components analysis, and whose rCBF was proven to significantly differ between groups, were considered for data analysis. These four factors were functionally connected clusters of Brodmann areas belonging to the temporo-parietal lobes (n=3) and to central structures (n=1) and were analysed together. The accuracy of the classification of eAD, AD and CTR utilising the K-means clustering method was separately tested for each group pair and for each region. Results: In AD/CTR evaluation, hippocampus uptake could correctly classify the 82.1% of the subjects, while the accuracy of both temporo-parietal lobes and the four joint factors was 96.4%. When the correct classification to eAD/CTR groups was tested, the accuracy of 99m-Tc-HMPAO uptake intensity in discriminating the groups was 85.4% for hippocampus, 80.5% for temporo-parietal lobes and 87.8% for the four joint factors. Discussion: Utilising separately sensitive regions (hippocampus), lobes (temporo-parietal) and functionally connected regions in classifying eAD and AD yielded different results. Severe AD was better classified by data from lobes and from the functionally connected regions affected by the disease. Early AD was classified with higher accuracy by hippocampus and the functionally connected regions in temporo-parietal lobes and central structures. Such differences are consistent with the progression of the disease which is supposed to start in the medial temporal lobe and spread through the temporo-parietal cortex. The proposed method adds information mainly in the early stage of the disease.