IBZM SPECT and FDG PET in the differential diagnosis of Parkinsonian syndromes. Comparison with respect to inter-rater agreement

Both IBZM SPECT and FDG PET may be used for differentiation between Parkinson's disease (PD) and atypical neurodegenerative parkinsonian syndromes (APS). However, there are only very limited data of both modalities in the same subjects. The present study compared both modalities with respect to inter-rater agreement in 30 patients with neurodegenerative parkinsonian syndromes (PS) confirmed by FP-CIT SPECT. IBZM SPECT and FDG PET were categorized as PD or APS by visual inspection of standardized report pages and statistical parametric maps (SPMs). Categorization was performed independently by five readers. Inter-rater agreement was quantified using Cohen's kappa κ. IBZM SPECT resulted in PD and APS in 11 and 19 cases, respectively (majoritarian categorization). Inter-rater agreement was κ=0.64±0.10. FDG PET resulted in PD and APS in 12 and 18 cases, respectively (majoritarian categorization). Inter-rater agreement was κ=0.68±0.07. Majoritarian diagnosis disagreed between IBZM SPECT and FDG PET in 13 cases (43%). Semi-quantitative analysis of IBZM SPECT using the striatum-to-reference distribution volume ratio was in good agreement with visual categorization (area under ROC curve 0.92). In neurodegenerative PS, inter-rater agreement of visual analysis is substantial in both IBZM SPECT and FDG PET. Furthermore, (I) visual analysis of IBZM SPECT is reliable if adequate standardized image display is used, (II) visual analysis of FDG SPMs allows unique categorization as either PD or APS in most subjects, and (III) IBZM SPECT and FDG PET are discordant in a significant fraction of cases. (orig.)