Meta-analysis of the literature on diagnostic accuracy of SPECT in Parkinsonian syndromes

Background: Parkinson's disease (PD) is the second most common neurodegenerative disorder. One of the most widely used techniques to diagnose PD is a Single Photon Emission Computer Tomography ( SPECT) scan to visualise the integrity of the dopaminergic pathways in the brain. Despite this there remains some discussion on the value of SPECT in the differential diagnosis of PD. We did a meta-analysis of all the existing literature on the diagnostic accuracy of both pre- and post-synaptic SPECT imaging in the differential diagnosis of PD. Methods: Relevant studies were searched in Medline, EMBASE and Cochrane databases with back-searching of their reference lists. We limited our analysis to studies with a clinically relevant methodology: i.e. when they assessed the ability of the SPECT to provide 1. diagnosis of PD in an early phase vs. normalcy; 2 diagnostic differentiation between PD and essential tremor ( ET); 3. distinguishing between PD and vascular parkinsonism (VP); 4. delineation of PD from atypical parkinsonian syndromes (APS). Gold standard was, dependent on the study type, clinical examination at initial visit or follow-up, and/or response to dopaminergic agents. Results: The search gave 185 hits, of which we deemed 32 suitable for our analysis. From these we recalculated the diagnostic odds ratio of SPECT for the clinical questions above. The pooled odds ratio ( with 95% Cl) for presynaptic SPECT scan's ability to distinguish between early PD and normalcy was 60 ( 13 - 277). For the ability to differentiate between PD and ET this ratio was 210 ( 79 - 562). The ratio for presynaptic SPECT's ability to delineate PD from VP was 105 ( 32 - 348). The mean odds ratio for the presynaptic SPECT scans to differentiate between PD and the two APS was 2 ( 1 - 4), and for the postsynaptic SPECT imaging this was 19 ( 9 - 36). Conclusion: SPECT with presynaptic radiotracers is relatively accurate to differentiate patients with PD in an early phase from normalcy, patients with PD from those with ET, and PD from VP. The accuracy of SPECT with both presynaptic and postsynaptic tracers to differentiate between PD and APS is relatively low.