Transcranial brain sonography findings in Parkinson's disease: implications for pathogenesis, early diagnosis and therapy.

In Parkinson's disease (PD) transcranial sonography (TCS) reveals changes of several deep brain structures that are related to distinct motor and nonmotor features. Approximately 90% of PD patients exhibit substantia nigra (SN) hyperechogenicity, which is stable over time and discriminates PD from atypical parkinsonian disorders. Since this TCS feature is also present in 9% of healthy adults aged 18-80 years, and is associated with a subclinical malfunction of the nigrostriatal dopaminergic system, it is considered to be a risk marker for PD. SN hyperechogenicity is caused by increased amounts of iron, probably in abnormal protein bindings, and could be related in some cases to mutations of genes involved in iron metabolism. Influencing the disturbances of iron metabolism reflected by SN hyperechogenicity early in life might become a future therapeutic target for PD. Longitudinal studies currently assess the value of SN hyperechogenicity in combination with clinical and other neuroimaging findings in predicting an individual high risk of PD. TCS has the potential of a cost-effective, quick and mobile screening tool for risk populations within a stepwise diagnostic scheme to select individuals for upcoming neuroprotective therapies. This review summarizes TCS findings, shedding light on the pathophysiology of PD, and discusses their potential therapeutic relevance.