Vulnerability of the nigrostriatal system as detected by transcranial ultrasound

Objective: To assess the incidence of a hyperechogenic substantia nigra (SN ) by transcranial sonography (TCS) in healthy people and to evaluate whethe r an enlarged hyperechogenic SN area is associated with functional impairme nt of the nigrostriatal system. Background and Methods: Until now, preclini cal impairment of the nigrostriatal system could be identified only by func tional neuroimaging techniques such as PET in selected groups of patients. TCS is a new, noninvasive ultrasound technique that has demonstrated an inc reased echogenicity of the SN in patients with PD, whereas in most healthy individuals, the SN is either barely detectable or undetectable by TCS. Res ults: Of 330 healthy volunteers, 8.6% exhibited an increased echogenicity o f the SN. From these, 10 clinically healthy individuals with distinct unila teral or bilateral hyperechogenic signals in the SN region (SN area above 0 .25 cm(2)) underwent comprehensive motor testing, neuropsychological assess ment, MRI, and [F-18]-dopa PET examination. With regard to motor functions, these individuals did not differ from 10 age- and sex-matched controls wit h a low echogenic SN and an area of echogenic signals below 0.2 cm(2). Enla rgement of hyperechogenic areas in the 10 healthy individuals was associate d with a marked decrease in the accumulation of [F-18]-dopa in the caudate nucleus and putamen. Conclusions: Substantia nigra hyperechogenicity appear s to indicate a functional impairment of the nigrostriatal system. Transcra nial sonography may be a suitable method of identifying persons at risk of nigrostriatal alterations, making possible the introduction of early neurop rotective therapy.