DISCRIMINATIVE USE OF SPECT IN FRONTAL LOBE-TYPE DEMENTIA VERSUS (SENILE) DEMENTIA OF THE ALZHEIMERS TYPE

Dementia of the Alzheimer's type [(S)DAT] and dementia with frontal fe atures (FLD) are nosological entities with different prognoses and pre sumed pathophysiology. There is a need for noninvasive differential di agnostic tools. To evaluate whether SPECT perfusion imaging could disc riminate between these neurodegenerative disorders, we performed a com parative study. Methods: SPECT scans using Tc-99m-hexamethylpropylene amine oxime (Tc-99m-HMPAO) of 21 patients with FLD were compared with those obtained in a group of 19 age- and severity-matched patients suf fering from (S)DAT. Brain SPECT perfusion deficits were scored by visu al qualitative analysis with respect to location, lateralization and s everity. A total severity score of cerebral hypoperfusion (maximal val ue = 18) was calculated by adding all severity scores (scored between 0 and 3; 0 = no perfusion deficit; 1 = 13%-30% hypoperfusion; 2 = 30%- 50% hypoperfusion and 3 = >50% hypoperfusion including breaching of th e cortex) for right and left frontal, parietal and temporal lobes. Mor eover, bifrontal hypoperfusion (F-s) was scored, yielding a value betw een 0 and 6 by adding the two frontal severity scores. Results: No sig nificant correlation was found between MMSE scores and total severity scores on SPECT. A statistically significant correlation was found bet ween the Middelheim frontality score and frontal severity score. Stati stically more significant bilateral hypoperfusion of the parietal lobe s was found in the (S)DAT group. Conversely, bifrontal hypoperfusion w as found more in the FLD group. Stepwise logistic regression analysis identified the severity of bifrontal hypoperfusion as the most signifi cant contributing parameter to correctly classifying (S)DAT versus FLD on SPECT. The probability of predicting (S)DAT based on the SPECT sca n is calculated with the following formula: p(DAT) = 1/[1 + e(-(1.1-0. 661xFs))]. Using this equation, a value above 0.5 was predictive for ( S)DAT and a calculated value under 0.5 was predictive for FLD. Using t his model, 81% of the FLD group and 74% of the (S)DAT were correctly c lassified. Conclusion: Technetium-99m-HMPAO SPECT may help in discrimi nating FLD from (S)DAT. Bifrontal hypoperfusion was found to be the mo st powerful predictor of clinical classification. Further validation o f the presented logistic regression model is warranted.