A CLINICAL ROLE FOR TC-99M-HMPAO SPECT IN THE INVESTIGATION OF DEMENTIA

Objectives-To provide the clinician with a guide to the clinical utili ty of Tc-99m-HMPAO single photon emission computed tomography (SPECT) and to the interpretation of specific test results in the differential diagnosis of dementia. Methods-Three hundred and sixty three patients with dementia were studied prospectively for a median three (range 1- 6) years and classified into disease groups on the basis of establishe d clinical criteria. The degree to which different patterns of cerebra l blood flow (CBF) abnormality found on Tc-99m-HMPAO SPECT imaging at the time of initial patient presentation modified clinical diagnoses w as determined by calculating the Likelihood ratios for pairwise diseas e group comparisons. The optimal clinical usage of Tc-99m-HMPAO SPECT was determined by calculating the percentage of significant test resul ts for each pairwise disease group comparison. Results-Bilateral poste rior CBF abnormality was found to significantly increase the odds of a patient having Alzheimer's disease as opposed to vascular dementia or frontotemporal dementia. Bilateral anterior CBF abnormality significa ntly increased the odds of a patient having frontotemporal dementia as opposed to Alzheimer's disease, vascular dementia, or Lewy body disea se. ''Patchy'' CBF changes significantly increased the odds of a patie nt having vascular dementia as opposed to Alzheimer's disease. Unilate ral anterior, unilateral anterior plus unilateral posterior, and gener alised CBF abnormality failed to contribute to the differentiation of any of these forms of dementia. Conclusions-Tc-99m-HMPAO SPECT was fou nd to be most useful in distinguishing Alzheimer's disease from vascul ar dementia and fronto temporal dementia, and least useful in differen tiating between Alzheimer's disease and Lewy body disease, and between vascular dementia, frontotemporal dementia, and progressive aphasia. It is suggested that CBF SPECT should be used selectively and as an ad junct to clinical evaluation and CT.