Role of single photon emission computerized tomography (SPECT) in diagnosis of early cognitive impairment in the elderly

Objective: The aim of this study is to assess brain perfusion SPECT as a diagnostic tool in detection of subclinical cognitive deficits in non-demented elderly people. METHODS: The tracer distribution was measured with Tc99m-HMPAO and SPECT in 37 elderly subjects; age range 60-84 yrs. Results: Patients were divided according to Mini-Mental State Examination (MMSE) into 3 groups: Group II with global cognitive impairment (GCI) without dementia (45.95%); Group I without cognitive impairment (54.05%), further subdivided according to Clinical Dementia Rating Scale (CDR) into normal elderly (27.03%) and those with questionable cognitive decline (QCD) (27.03%), a term used for cases fulfilling criteria of mild cognitive impairment but did not significantly differ from normal elderly as regards their scores on neuropsychological testing as well as their ability to carry out daily functional activities. Nevertheless, brain SPECT using Tc99m-HMPAO showed significant difference in QCD cases from normal elderly in mean perfusion of bilateral frontal lobes, left temporal lobe, right thalamus, right basal ganglia and right occiptal lobe. On the other hand, neuropsychological testing and mean perfusion of bilateral frontal, bilateral temporal, left parietal, left occipital and left thalamic regions were significantly less in Group II compared to Group I. Mean asymmetry index (MAI) exceeded 10% in regions of basal ganglia (11%) and thalamus (11%) of cases with QCD as well as in temporal region (10.1%) of cases with GCI. Sensitivity of our SPECT findings in detecting early cognitive impairment increased from 29.4% by visual analysis to 64.7% by quantitative analysis, while specificity decreased from 60% to 45%. Temporal hypoperfusion, by quantitative analysis, was 60% predictive of cognitive decline; while predictive value of thalamic hypoperfusion was 50%. Decreased brain perfusion was significantly associated with cognitive decline and low education level but not with advancing age. HMPAO uptake of right frontal, parietal and bilateral occipital lobes was significantly more in females compared to males These changes were not related to vascular risk factors. Conclusion: It is therefore suggested that cerebral blood flow (CBF) imaging should be used selectively and as an adjunct to clinical evaluation and Computerized Tomography (CT) in the investigation of dementia. With semi-quantitative analysis, group differences can often be detected, but the problem for the clinician is the application of such results to the individual case. . (Egypt J. Neurol. Psychiat. Neurosurg., 2004, 41(1): 59-77).