Substantia nigra hyperechogenicity as a marker for Parkinson's disease: a population-based study

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.

To evaluate SN hyperechogenicity as a marker for PD in the Bruneck Study cohort, which is representative of the general elderly community.

The diagnostic accuracy of TCS in distinguishing clinically diagnosed PD from nonparkinsonian subjects was assessed in 574 subjects from this cohort.

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 cm(2), 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.

SN hyperechogenicity may represent a useful biomarker for PD not only in a hospital-based setting but also in the general community.