Evaluating the Swallow-Tail Sign on susceptibility-weighted imaging (SWI) for Parkinson's disease diagnosis: A bivariate meta-analysis.

BACKGROUND AND PURPOSE: The Swallow-Tail Sign (STS), reflecting nigrosome-1 integrity in the substantia nigra, is a magnetic resonance imaging biomarker for Parkinson's disease (PD). Although susceptibility-weighted imaging (SWI) is widely available, the diagnostic performance of STS on SWI has not been comprehensively quantified. This study evaluated the diagnostic accuracy of STS on SWI for identifying PD. MATERIALS AND METHODS: MEDLINE, Embase, and Web of Science were searched for studies assessing STS on SWI in adults with clinically diagnosed PD and healthy controls. Eligible studies provided data to construct 2 × 2 tables. Methodological quality was assessed with QUADAS-2. A bivariate random-effects model estimated pooled sensitivity, specificity, likelihood ratios, and diagnostic odds ratio. RESULTS: Seventeen studies including 1008 PD patients and 944 controls were analyzed. Pooled sensitivity was 0.91 (95% CI: 0.83-0.96) and specificity 0.89 (95% CI: 0.82-0.93). The positive likelihood ratio was 8.1 and the negative likelihood ratio 0.10. The diagnostic odds ratio was 83, and the area under the curve was 0.95. Substantial heterogeneity was observed without evidence of publication bias. CONCLUSIONS: STS on SWI demonstrates high diagnostic accuracy for PD and represents a reliable, non-invasive adjunct to clinical diagnosis.