If you’ve ever kicked, punched or shouted in your sleep, you might have brushed it off as a bad dream. But for some people, these movements could be an early warning sign of Parkinson’s. 

A new study led by Dr. Shady Rahayel, funded by Parkinson Canada, is helping us understand how a specific sleep disorder might predict who will develop Parkinson’s years before symptoms appear. 

When dreams become reality 

The condition is called idiopathic REM sleep behaviour disorder, or iRBD. During normal REM sleep, our bodies are essentially paralyzed – a protective mechanism that keeps us from acting out our dreams.  People with iRBD don’t have that protection. They physically act out their dreams through sudden movements, talking, or shouting. 

Researchers have known for years that iRBD is often an early warning sign of Parkinson’s or dementia with Lewy bodies (DLB). But here’s the problem: not everyone with iRBD develops these conditions. And until now, doctors couldn’t predict who would. 

Two paths, two outcomes 

Dr. Rahayel’s team followed 362 people with iRBD for at least five years, using MRI scans and neurological assessments to track brain changes over time.  They discovered something important: brain degeneration in iRBD doesn’t follow one path. It follows two distinct patterns. 

The first group showed “cortical-first” degeneration – the outer brain regions broke down first. These people were more likely to develop cognitive problems and DLB. 

The second group showed “subcortical-first” degeneration – deeper brain regions were affected first. These people were more likely to develop classic Parkinson’s motor symptoms like tremor and rigidity. 

Why this matters 

iRBD often shows up years, sometimes decades, before Parkinson’s symptoms begin. If doctors could identify which subtype someone has early on, they could tailor treatment to that person’s specific risk. 

Earlier diagnosis. Earlier intervention. Treatment when it might matter most. 

This research opens the door to precision medicine – personalized care based on what’s happening in each person’s brain, not a one-size-fits-all approach. 

Looking ahead 

Not everyone with iRBD will develop Parkinson’s. But for those who do, understanding which path their brain is taking could make all the difference. As research continues, these findings could lead to clinical tools doctors can use when someone first shows signs of iRBD. Something that gives answers earlier, when intervention might matter most. 

Parkinson Canada is proud to have funded this research, published in eBioMedicine. Studies like this bring us closer to spotting Parkinson’s before it starts. 

References 

Joza, S., Delva, A., Tremblay, C., Vo, A., Filiatrault, M., Tweedale, M., Gagnon, J. F., Postuma, R. B., Dagher, A., Klein, J., Hu, M., Dusek, P., Marecek, S., Varga, Z., Taylor, J. P., O’Brien, J. T., Firbank, M., Thomas, A., Donaghy, P. C., … Rahayel, S. (2025). Distinct brain atrophy progression subtypes underlie phenoconversion in isolated REM sleep behaviour disorder. eBioMedicine, 117, 105753.