Study Suggests Brain Tissue Iron May Track Cognitive Involvement in Parkinson

Brain tissue iron, measured with quantitative susceptibility mapping (QSM), can track cognitive involvement in Parkinson disease (PD), according to a study published by the Journal of Neurology, Neurosurgery, and Psychiatry.

The researchers used the Montreal Cognitive Assessment (MoCA), a clinical algorithm for risk of cognitive decline in PD, to evaluate 100 patients with early-stage to mid-stage PD as well as 37 age-matched controls. The researchers also measured visuoperceptual functions and the movement Disorders Society Unified Parkinson’s Disease Rating Scale part 3 (UPDRS-III). The study compared the associations between these measures and QSM—a magnetic resonance imaging (MRI) technique sensitive to brain tissue iron content.

"Iron in the brain is of growing interest to people researching neurodegenerative diseases such as Parkinson's and dementias. As you get older, iron accumulates in the brain, but it's also linked to the build-up of harmful brain proteins, so we're starting to find evidence that it could be useful in monitoring disease progression, and potentially even in diagnostics," the study's lead author, Rimona Weil, PhD, UCL Queen Square Institute of Neurology, said in a statement.

The results demonstrated the QSM increases in PD compared to controls in prefrontal cortex and putamen. Additionally, the whole brain regression analyses within the PD group had identified QSM increases covarying with lower MoCA scores in the hippocampus and thalamus, with poorer visual function and with higher dementia risk scores in parietal, frontal and medial occipital cortices, and with higher UPDRS-III scores in the putamen, according to the authors. However, the study noted that atrophy demonstrated no differences between groups or in an association with clinical measures.

“We used QSM to identify brain tissue iron changes relating to poorer cognition in PD. For the first time, we showed tissue changes within hippocampus and thalamus relating to cognitive deficits in PD without dementia, and that brain iron increased in parietal and prefrontal cortices relating to predictors of poor cognitive outcome,” the authors said. “Additionally, we showed that brain iron increased in the putamen in relation to poorer motor function.”

The study results suggest that iron deposition may be valuable to track if a treatment is working in a clinical trial and could be used in the future for early diagnosis of PD or other neurodegenerative diseases.

"It's really promising to see measures like this which can potentially track the varying progression of Parkinson's disease, as it could help clinicians devise better treatment plans for people based on how their condition manifests, " said first author, doctoral student George Thomas (UCL Queen Square Institute of Neurology).

Reference

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]. Journal of Neurology, Neurosurgery & Psychiatry. J Neurol Neurosurg Psychiatry Res. doi: 10.1136/jnnp-2019-322042.