Substantia nigra hyperechogenicity is a risk marker of Parkinson's disease: yes

Abstract

As there is increasing evidence that the neurodegenerative process in Parkinson's disease (PD) starts years to decades before clinical symptoms allow diagnosis, markers for the identification of subjects at risk are eagerly sought after in order to allow an earlier, disease modulating or even neuroprotective therapy. In recent years, transcranial sonography (TCS) has evolved as a useful instrument in the differential diagnosis and also very early diagnosis of PD. The typical hallmark for PD, hyperechogenicity at the anatomical site of the substantia nigra (SN), can also be found in about 10% of healthy subjects. There is accumulating evidence that SN hyperechogenicity discloses a vulnerability of the nigrostriatal system in at least some of these persons. Moreover, an association of the ultrasound sign with a number of risk and premotor markers has been shown. However, the most striking argument for a relevance of SN hyperechogenicity in healthy subjects can be derived from the observation that some initially healthy subjects with SN hyperechogenicity developed PD in the long run, an observation which has led to longitudinal studies on the predictive value of the ultrasound sign for the development of PD. A first follow up after 3 years of a large cohort of at baseline extrapyramidally healthy individuals revealed a relative risk for incident PD 17.37 times higher in subjects with SN hyperechogenicity at baseline compared to those without this echomarker. Taken together, there is encouraging evidence to implement TCS in a screening battery to identify subjects at risk for the development of PD.