Relationship of substantia nigra echogenicity and motor function in elderly subjects

Background: Patients with Parkinson's disease (PD) exhibit an increased echogenicity of the substantia nigra (SN) on transcranial sonography. Some healthy adults with the same echo characteristics showed a reduced (18)fluorodopa uptake on PET, indicating a subclinical alteration of the nigrostriatal system. Objectives: To determine whether the sonographic phenotype of hyperechogenic SN has any relevance for motor function in elderly subjects and whether an increased echogenicity of the SN is associated with an impaired motor function. Method: In a population-based, cross-sectional study, 93 subjects older then 60 years without history of extrapyramidal disorder underwent sonographic and neurologic examinations, with a quantitative motor assessment. Results: Elderly healthy subjects without prediagnosed extrapyramidal disorder but with SN hyperechogenicity had more frequent and more severe parkinsonian symptoms and a slower finger tapping than those with a regular echogenicity of the SN (p < 0.05, U test). Conclusion: With increasing age, subjects with SN hyperechogenicity develop a more substantial slowing of movements than subjects without this echo pattern, stressing the functional relevance of this sonographic finding. The authors speculate that hyperechogenicity of the SN may be detected by transcranial sonography early in life and may serve as a risk marker for nigral injury, although only a minority of these subjects will develop the full clinical picture of PD.