Objectives: Alzheimer’s disease (AD) and Frontotemporal dementia (FTD) are the commonest causes of presenile dementia. In the absence of a biological marker diagnosis is reliant on clinical evaluation. Confirmation is often sought from neuroimaging, including SPECT. Most previous SPECT studies lack pathological validation. The aim of this study is to examine the accuracy of SPECT in differentiating FTD from AD in patients with subsequent pathological confirmation.
Methods: 99mTc-HMPAO SPECT images obtained at initial evaluation in 25 pathologically confirmed cases of FTD were examined. These images were visually rated by an experienced blinded Nuclear Medicine consultant and compared to those of 31 AD patients, also with pathological validation.
Results: A reduction in frontal cerebral blood flow (CBF) was more common in FTD and of diagnostic value (sensitivity 0.8, specificity 0.65 and +LR 2.25, CI 1.35-3.77). A pattern of bilateral frontal CBF reduction without the presence of associated bilateral parietal CBF change is diagnostically more accurate (sensitivity 0.80, specificity 0.81 and +LR 4.13, CI 1.96-8.71). Diagnostic categorization (FTD or AD) on SPECT alone was less accurate than clinical diagnosis (based on neurology and detailed neuropsychological evaluation). One FTD patient was initially misdiagnosed clinically as AD due to lack of availability of full neuropsychological assessment. However, SPECT correctly diagnosed this patient providing a diagnostic gain of 4%.
Conclusion: 99mTc-HMPAO SPECT CBF patterns provide valuable information in the diagnosis of FTD and AD. These data are better used as an adjunct to clinical diagnosis if pathology is to be correctly predicted in life.
- frontotemporal dementia