Eye Tests Predict Parkinson’s-Associated Cognitive Decline 18 Months Ahead

Simple vision tests can predict which people with Parkinson’s disease will develop cognitive impairment and possible dementia 18 months later, according to a study published in Movement Disorders.

The findings add to evidence that vision changes precede the cognitive decline that occurs in many, but not all, people with Parkinson’s disease.

In another study published in Communications Biology, the same research team found that structural and functional connections of brain regions become decoupled throughout the entire brain in people with Parkinson’s disease, particularly among people with vision problems.

The 2 studies together show how losses and changes to the brain’s wiring underlie the cognitive impairment experienced by many people with Parkinson’s disease.

“We have found that people with Parkinson’s disease who have visual problems are more likely to get dementia, and that appears to be explained by underlying changes to their brain wiring,” said lead author Angeliki Zarkali, MD, Dementia Research Centre, University College London Queen Square Institute of Neurology, London, United Kingdom. “Vision tests might provide us with a window of opportunity to predict Parkinson’s dementia before it begins, which may help us find ways to stop the cognitive decline before it’s too late.”

For the Movement Disorders paper, the researchers studied 77 patients with Parkinson’s disease and found that simple vision tests predicted who would go on to get dementia 1.5 years later. The study also found that those who went on to develop Parkinson’s dementia had losses in the wiring of the brain, including in areas relating to vision and memory. The researchers identified white matter damage to some of the long-distance wiring connecting the front and back of the brain, which helps the brain to function as a cohesive whole network.

The Communications Biology study involved 88 people with Parkinson’s disease (33 of whom had visual dysfunction and were thus judged to have a high risk of dementia) and 30 healthy adults as a control group, whose brains were imaged using MRI scans. The researchers found that people with Parkinson’s disease exhibited a higher degree of decoupling across the whole brain. Areas at the back of the brain, and less specialised areas, had the most decoupling in patients with Parkinson’s disease. Patients with Parkinson’s disease with visual dysfunction had more decoupling in some, but not all brain regions, particularly in memory-related regions in the temporal lobe.

The research team also found changes to the levels of some neurotransmitters in people at risk of cognitive decline, suggesting that receptors for those transmitters may be potential targets for new drug treatments for Parkinson’s dementia. Notably, while dopamine is known to be implicated in Parkinson’s, the researchers found that other neurotransmitters — acetylcholine, serotonin, and noradrenaline — were particularly affected in people at risk of cognitive decline.

“The 2 papers together help us to understand what’s going on in the brains of people with Parkinson’s who experience cognitive decline, as it appears to be driven by a breakdown in the wiring that connects different brain regions,” said Dr. Angeliki.

“Our findings could be valuable for clinical trials, by showing that vision tests can help us identify who we should be targeting for trials of new drugs that might be able to slow Parkinson’s — and ultimately if effective treatments are found, then these simple tests may help us identify who will benefit from which treatments,” said senior author Rimona Weil, MD, University College London.

References: https://onlinelibrary.wiley.com/doi/10.1002/mds.28477 and https://www.nature.com/articles/s42003-020-01622-9

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