Single photon emission computed tomography (SPECT) and magnetic resonance (MR) imaging data were obtained in 11 patients with dementia of the Alzheimer type (DAT), 11 with multi-infarct dementia (MID) and nine elderly, healthy controls. All patients with dementia tolerated a 15-minute SPECT scan while six patients (27%) did not tolerate the MR examination due to the long acquisition times and/or claustrophobia. Blind qualitative rating of SPECT scans differentiated correctly between dementia and controls in 90% of cases (p < 0.0001; positive predicted value of 91%) and between clinically defined DAT and MID in 77% of cases (p < 0.01; positive predicted value of 80%). It correctly identified clinical group membership (control, DAT or MID) in 71% of cases (p < 0.0001). Blind qualitative MR imaging analysis differentiated between dementia and controls in 91% of cases (p < 0.001; predicted positive value of 94%) but failed to differentiate between DAT and MID (positive predicted value of 50%). Overall, MR imaging correctly identified clinical group membership in 61% of cases (p < 0.01).
Semiquantitative SPECT data demonstrated reduced regional cerebral blood flow (rCBF) in all regions of interest (ROI) except right frontal and right anterior parietal in both DAT and MID compared with controls (p < 0.05).
There was no statistically significant difference between DAT and MID subjects in rCBF in any ROI. Several correlations between rCBF and cognitive variables were found in the MID but not the DAT group. Though the sample in this study is small, our findings suggest that Tc-99m HMPAO SPECT is a useful and practical tool in the assessment of patients with dementia. It enables the differential diagnosis of dementia and by using semiquantitative data it helps to establish the severity of disease. KEY woRDs-Alzheimer's disease, multi-infarct dementia, radionuclide imaging, magnetic resonance imaging, single photon emission computed tomography.
Dementia in old age is common, occurring in up to 7% of the population aged 65 and over (Livingston et al., 1990). The differential diagnosis