Single-photon emission computed tomography perfusion imaging in the differential diagnosis of dementia: a retrospective regional audit

A retrospective audit of (99m)Tc-HMPAO SPECT scans was undertaken to assess the utility of brain perfusion imaging in a cohort of young cognitively impaired patients in whom diagnostic uncertainty remained after standard clinical and neuropsychological assessment and structural brain imaging. SPECT scans were assessed by five raters (two neurologists and three nuclear medicine specialists) on two occasions 6 months apart, first without any clinical data and second with brief pertinent clinical information. SPECT diagnoses were compared with criterion diagnoses subsequently established by the two neurologists with access to all clinical, neuropsychological and neuroimaging data. Despite reasonable intra- and interrater reliability, diagnostic accuracy ranged from 32 to 58%. SPECT scan normality or abnormality in blind and informed viewings gave respective sensitivities of 77 and 71%, specificities of 44 and 38%, positive predictive values of 88 and 87% and negative predictive values of 27 and 18%. Calculating pairwise disease group comparisons, likelihood ratios suggested some diagnostic gain in differentiating AD from 'not AD' and from FTD/focal syndromes. SPECT scanning was of little help in establishing diagnoses in this cohort of patients, a finding which supports the conclusion of the American Academy of Neurology evidence-based review that SPECT imaging cannot be recommended for either the initial or the differential diagnosis of suspected dementia because it has not demonstrated superiority to clinical criteria.