Supplementary Material for: Substantia Nigra Hyperechogenicity as a Marker for Parkinson's Disease: A Population-Based Study

Background: The clinical diagnosis of Parkinson's disease (PD) is currently anchored in its cardinal motor symptoms. According to hospital-based studies, an enlarged echogenicity in the area of the substantia nigra (SN) assessed with transcranial sonography (TCS) may represent a useful biomarker in the diagnosis of PD. Objective: To evaluate SN hyperechogenicity as a marker for PD in the Bruneck Study cohort, which is representative of the general elderly community. Methods: The diagnostic accuracy of TCS in distinguishing clinically diagnosed PD from nonparkinsonian subjects was assessed in 574 subjects from this cohort. Results: There was a good diagnostic accuracy of TCS in distinguishing PD subjects from nonparkinsonian subjects with an area under the curve value of 0.82. At a receiver-operating characteristic curve analysis-based cutoff value for SN hyperechogenicity of 0.18 cm², TCS had a sensitivity of 88.2% (95% confidence interval, CI, 64.4-98.0), a specificity of 77.0% (95% CI 72.8-80.6), a positive predictive value of 12.7% (95% CI 7.8-20.0) and a negative predictive value of 99.4% (95% CI 97.8-100.0) for subjects with clinically definite PD at baseline. When analyzing the same population after 5 years with regard to the presence of known and newly diagnosed PD cases, baseline TCS yielded very similar diagnostic accuracy values. Conclusion: SN hyperechogenicity may represent a useful biomarker for PD not only in a hospital-based setting but also in the general community.