Cognitive Performance Patterns in Healthy Individuals with Substantia Nigra Hyperechogenicity and Early Parkinson's Disease

Introduction: Hyperechogenicity of the substantia nigra (SN+) is a risk marker for Parkinson’s disease (PD) that can be detected prior to diagnosis. In healthy individuals, SN+ has been linked to mild cognitive deficits, suggesting possible pre-diagnostic cognitive changes. However, these deficits have not been directly compared with those seen in PD.

Methods: Cognitive data from 262 healthy individuals with normal echogenicity (SN-), 48 healthy individuals with SN+, and 82 early PD patients were assessed using the CERAD test battery. Principal component analysis identified cognitive domains, and group differences were analyzed using variance analyses. The proportion of individuals with abnormal performance (z < −1.0) was also compared.

Results: Verbal memory, semantic/executive function, and praxis were identified as cognitive components. The SN+ group performed worse than the SN- group in semantic and executive functions, with a trend toward reduced verbal memory. SN+ individuals scored significantly lower on the Boston Naming Test. PD patients showed higher rates of abnormal performance overall, while SN+ individuals more frequently showed deficits in naming and executive tasks than SN- controls.

Conclusion: Healthy individuals with SN+ show specific cognitive impairments compared to SN- individuals. However, their cognitive profile differs from that of early PD, suggesting partially distinct underlying mechanisms, possibly due to compensation or the fact that not all SN+ individuals develop PD.