Comparison of biospecimens for α‐synuclein seed amplification assays in Parkinson's disease: A systematic review and network meta‐analysis

Abstract Background and purpose Alpha‐synuclein seed amplification assays (α‐syn SAAs) are promising diagnostic methods for Parkinson's disease (PD) and other synucleinopathies. However, there is limited consensus regarding the diagnostic and differential diagnostic performance of α‐syn SAAs on biofluids and peripheral tissues. Methods A comprehensive research was performed in PubMed, Web of Science, Embase and Cochrane Library. Meta‐analysis was performed using a random‐effects model. A network meta‐analysis based on an ANOVA model was conducted to compare the relative accuracy of α‐syn SAAs with different specimens. Results The pooled sensitivity and specificity of α‐syn SAAs in distinguishing PD from healthy controls or non‐neurodegenerative neurological controls were 0.91 (95% confidence interval [CI] 0.89‐0.92) and 0.95 (95% CI 0.94‐0.96) for cerebrospinal fluid (CSF); 0.91 (95% CI 0.86–0.94) and 0.92 (95% CI 0.87‐0.95) for skin; 0.80 (95% CI 0.66‐0.89) and 0.87 (95% CI 0.69‐0.96) for submandibular gland; 0.44 (95% CI 0.30–0.59) and 0.92 (95% CI 0.79–0.98) for gastrointestinal tract; 0.79 (95% CI 0.70–0.86) and 0.88 (95% CI 0.77–0.95) for saliva; and 0.51 (95% CI 0.39‐0.62) and 0.91 (95% CI 0.84‐0.96) for olfactory mucosa (OM). The pooled sensitivity and specificity were 0.91 (95% CI 0.89–0.93) and 0.50 (95% CI 0.44–0.55) for CSF, 0.92 (95% CI 0.83–0.97) and 0.22 (95% CI 0.06–0.48) for skin, and 0.55 (95% CI 0.42–0.68) and 0.50 (95% CI 0.35–0.65) for OM in distinguishing PD from multiple system atrophy. The pooled sensitivity and specificity were 0.92 (95% CI 0.89–0.94) and 0.84 (95% CI 0.73–0.91) for CSF, 0.92 (95% CI 0.83–0.97) and 0.88 (95% CI 0.64–0.99) for skin and 0.63 (95% CI 0.52‐0.73) and 0.86 (95% CI 0.64‐0.97) for OM in distinguishing PD from progressive supranuclear palsy. The pooled sensitivity and specificity were 0.94 (95% CI 0.90–0.97) and 0.95 (95% CI 0.77–1.00) for CSF and 0.94 (95% CI 0.84–0.99) and 0.86 (95% CI 0.42–1.00) for skin in distinguishing PD from corticobasal degeneration. Conclusions α‐Synuclein SAAs of CSF, skin, saliva, submandibular gland, gastrointestinal tract and OM are promising diagnostic assays for PD, with CSF and skin α‐syn SAAs demonstrating higher diagnostic performance.