Objective: After 4,5 years follow-up we re-evaluated 17 patients with probable AD according to NINCDS-ADRDA criteria, 11 subjects with evidence of mild cognitive impairment (MCI), and 13 age-matched healthy controls.
Design: Case-control, longitudinal SPECT study.
Materials and Methods: All subjects were submitted to the CAMDEX interview, the Mini-Mental State Examination (MMSE) and the cognitive sub-scale (CAMCOG) of the CAMDEX. The diagnostic work-up included laboratory exams and an MRI scan. SPECT scans were obtained with a single-detector SIEMENS system and the subjects received a 30-40 mCi 99mTc-HMPAO injection. Between-group regional cerebral blood flow (rCBF) differences and correlations with tests scores were investigated on a voxel-by-voxel basis using Statistical Parametric Mapping software (SPM99). In each analysis, inter-individual differences in global grey matter blood flow were accounted for by proportional scaling.
Results: There were no significant differences regarding the mean age, marital state, and years of schooling in the three groups. AD patients had a significantly worse overall cognitive performance compared to MCI cases and controls. Between-group SPM comparisons showed reduced rCBF in AD patients relative to controls in a large cluster encompassing the left posterior lateral temporal and parietal cortices (Zmax=3.61, Zmax=3.69; p<0.001). On the other hand, there were no significant rCBF differences between MCI subjects and healthy controls. Also, SPM comparisons showed areas of increased white matter tracer uptake in AD patients relative to controls, possibly as an artifactual consequence of the globally reduced grey matter rCBF in AD subjects. Finally, in the AD group, significant positive correlations corrected for age and schooling were found between: MMSE scores and left lateral prefrontal cortex rCBF (Zmax=3.53; p<0.001); CAMCOG scores and left lateral prefrontal cortex rCBF (Zmax=3.58; p<0.001); and CAMCOG memory subscale scores and rCBF in the right and left posterior temporal cortices (Zmax=4.23; p<0.001).
Conclusions: We have confirmed previous findings of reduced temporal and parietal rCBF in AD patients compared to age matched healthy controls. In addition, we have found significant positive correlations between prefrontal and temporal cortices rCBF and performance on cognitive tests in AD patients. The implications of such preliminary voxel-based SPECT finding using a single-detector system should be addressed in future studies.
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