Up to half of patients with Parkinson disease (PD) are also diagnosed with dementia, but tools to track changes in cognition are lacking. Because conventional neuroimaging is often not sensitive enough for tracking cognitive changes in patients with early-stage PD, researchers are exploring other options such as quantitative susceptibility mapping (QSM). Using QSM, researchers found evidence linking higher brain iron levels with cognitive changes. Results of this study are published in the Journal of Neurology, Neurosurgery, and Psychiatry.
The researchers recruited 100 patients with PD from age 49 to 80 years who had been diagnosed within the last 10 years. All continued their usual therapy throughout the study. In addition, the researchers recruited 37 age-matched control participants. Using a validated clinical algorithm, they assessed cognition, visual acuity, and motor function in the patients, as well as 2-year risk for cognitive decline. They then used QSM, a new MRI technique, to detect variations in iron content in the brains of patients. Brain iron levels are known to appear alongside Alzheimer’s pathology, particularly amyloid and tau, which are also key predictors of PD dementia. The researchers hoped that by detecting brain iron levels they could identify areas affected by what might eventually indicate PD dementia. After the MRI scans were completed, both whole-brain and cross-sectional analyses were performed. Voxel-based morphometry was also used to examine gray matter volume associations with various clinical parameters.
The results showed QSM increases in patients with PD vs control participants. Specifically, higher brain tissue iron content was observed in the prefrontal cortex and putamen. Patients with QSM increases also showed lower cognitive assessment scores in the hippocampus and thalamus, lower motor function, and higher dementia risk. However, atrophy measured via voxel-based morphometry showed no differences between the 2 study groups. This study marks the first time that variation in brain iron and changes in cognition and motor function were found to be associated. These changes were identified in regions in which conventional neuroimaging could not identify atrophy, indicating that iron changes and other patterns identified via QSM could serve as potential markers of PD activity.
Limitations of the study included segmentation into gray and white matter that may have distorted some of the findings in brain areas such as the posterior region. In addition, as the measurements in the study were obtained at a single point, further studies could be performed to explore QSM as a disease predictor over longer periods of time.
Thomas GEC, Leyland LA, Schrag A, et al. Brain iron deposition is linked with cognitive severity in Parkinson’s disease [published online February 20, 2020]. J Neurol Neurosurg Psychiatry. doi:10.1136/jnnp-2019-322042