SPECT as a diagnostic test in the investigation of dementia

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Abstract

Single photon emission tomography (SPECT) permits the assessment of the decrease of regional cerebral blood flow (rCBF). The aim of this study was to assess the relationship between the different types of dementia (Alzheimer's disease (AD), vascular dementia (VaD) and frontotemporal dementia (FTD)) and the rCBF in the SPECT examination. In patients with AD, the SPECT examination showed hypoperfusion in temporoparietal regions, contrary to patients with frontotemporal dementia, where hypoperfusion was limited to the frontal area, and compared to patients with VaD, where “patchy” rCBF changes were observed in different regions. In mild cases of AD, perfusion deficits were observed in the frontal regions equal to those in VaD. The study shows that the SPECT examination may be useful in distinguishing between AD, VaD, and FTD; however, for proper diagnosis in the early stages of AD, additional factors must be taken into consideration.

Introduction

Cognitive impairment is connected with a wide array of neurological diseases. Neuropsychological tests and neuroimaging (CT or MR) should be performed in every case of suspected dementia. However, these examinations are frequently insufficient for the proper diagnosis of the type of dementia: Alzheimer's disease (AD), vascular dementia (VaD), and frontotemporal dementia (FTD). With the present perspectives of effective treatment, a diagnosis of the type of dementia in the early stages will be of great clinical value.

Single photon emission tomography (SPECT) permits the assessment of the decrease of cortical perfusion in various regions of the brain and could potentially be a useful tool for the diagnosis of the different types of dementia. Neuropathological investigations have confirmed the good correlation between clinical and SPECT findings in AD [1]. Correlation between the regional cerebral blood flow (rCBF) and specific neuropsychological deficits in AD and FTD has also been reported [2], [3]. The prevailing opinion is that AD is connected with a decrease in rCBF in the temporoparietal cortex, while FTD, with a more pronounced decrease in rCBF in the frontal areas [4], [5], [6], [7], [8].

Despite these findings, the applicability of SPECT in the differentiation of dementia is still a subject of debate. According to Scheltens and Korf [9], the applicability of SPECT in early differential diagnosis seems limited. Furthermore, routinely used comparisons between SPECT results for AD and controls leads to varying results [10], [11], [12].

Relatively few papers have been concerned with the application of SPECT in the differentiation of VaD from FTD or AD. Talbot et al. [13] have shown that SPECT was most useful in distinguishing AD from VaD and FTD. On the other hand, it was least useful in differentiating between VaD and FTD. There are reports [14], [15], [16] indicating posterior rCBF abnormality in AD, “patchy” rCBF changes in VaD, and anterior rCBF abnormality in FTD.

These discrepancies indicate that SPECT, as a diagnostic tool in dementia, requires further investigation. Of particular interest is the occurrence of rCBF reductions in the frontal area in AD patients, because frontal hypoperfusion may occur in the early stage of AD.

The aim of the study was to assess the relation between the different types of dementia and blood flow disturbances in the SPECT examination.

Section snippets

Materials and methods

The sample consisted of 41 patients (16 male, 25 female, mean age 66.8±12.3) with dementia according to DSM-IV. All patients were subjected to a comprehensive medical evaluation. In all cases, CT or MR examinations were performed and neuropsychological tests were done: Mini Mental Status Evaluation, additional tests for the evaluation of visual and verbal memory constructional ability, visuospatial ability, language, praxis, and mood as a measure of disease severity. VaD was found in 10

Results

Neuropsychological tests have not only differentiated the severity of dementia but were also useful in the diagnosis of type of dementia. Fig. 1 shows the results of the Rey Auditory Verbal Test for the different types of dementia. The learning curve for moderate AD is lower than for all other types of dementia. Patients with FTD display the best results. The results of SPECT have shown measurements of the correlation between hypoperfusion in temporal regions (bilaterally) and the severity of

Discussion

The present results agree well with previous work [4], [5], [6], [7], [8], [22], [23], showing that the severity of the dementia correlates well with the loss of temporal cortical perfusion (Table 1). Jagust et al. [4] found a clear correlation between the severity of AD and hypoperfusion in the temporoparietal cortex. Charpentier et al. [5] have shown that AD and FTD are clearly differentiated by SPECT, and have derived a simple decision rule, based on factorial discriminant analysis. Although

Acknowledgements

The research was supported by the Institute of Psychiatry and Neurology, Warsaw, under contract 37/2001.

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