Transcranial ultrasound as a risk marker for Parkinson's disease

The question of early, even premotor, detection of Parkinson's disease (PD) has become a major issue because the effect of neuroprotective therapies depends on the time they are started. A number of clinical premotor markers which are helpful especially in the early diagnosis are being discussed; however, they are mostly unspecific and already signs of the progressing neurodegenerative process. An increasingly important risk marker for PD is genetic predisposition, as the number of known disease causing and modulating genes is increasing. Still, only the minority of PD cases can be attributed to monogenetic forms. Substantia nigra (SN) hyperechogenicity, assessed by transcranial sonography, has been shown to be a typical marker for PD. Because of its stability during the disease course, this echofeature is very helpful in early and differential diagnosis. Moreover, functional neuroimaging studies indicate a vulnerability of the nigrostriatal system of yet healthy subjects with SN hyperechogenicity. This vulnerability may become clinically relevant with age, under neuroleptic therapy, or under demanding motor tasks. The fact that still unaffected mutation carriers for monogenetic PD show this echofeature and that over the years some subjects with SN hyperechogenicity have already been observed to develop PD indicates that it may be regarded as a risk factor--a hypothesis which is currently being investigated in large prospective investigations.