REM Sleep Disorder: The Hidden Early Sign of Parkinson's and Dementia

Imagine acting out your dreams- thrashing, shouting, even punching- while you’re asleep. For many, this may sound like a funny story, but in medical terms, it is a red flag. This condition is known as isolated REM sleep behavior disorder (iRBD), and new research presented at the European Respiratory Society (ERS) Congress highlights how it could predict the onset of serious neurological diseases like Parkinson's disease and dementia with Lewy bodies (DLB) years before they appear (1^✔ ✔Trusted Source
Does isolated REM sleep behaviour disorder predict Parkinson’s disease or dementia?

Go to source). The groundbreaking study, conducted by an international team led by Université de Montréal, has identified two biomarkers that can help distinguish which patients with iRBD are more likely to develop Parkinson’s and which are likely to develop dementia. This development could transform the way doctors approach prevention and early treatment of neurodegenerative diseases.

What Is Isolated REM Sleep Behavior Disorder (iRBD)?

Normally, during REM (rapid eye movement) sleep, our brain temporarily paralyzes most muscles so we don’t physically act out our dreams. But in people with iRBD, this protective mechanism fails. As a result, they may yell, kick, punch, or even injure themselves or their bed partners while dreaming.

Although iRBD might look like a quirky sleep problem, it is far more significant. Research shows that nearly 90% of people with iRBD eventually develop a neurodegenerative disease, particularly Parkinson’s or DLB. Until recently, however, doctors could not tell which disease would follow- or how soon.

Biomarker Discovery #1: Brain Glymphatic Function and Parkinson’s

In the first study, published in Neurology, researchers analyzed 428 participants across five countries. They focused on the brain’s glymphatic system, a network that clears waste from the brain, including toxic proteins linked to neurodegeneration.

Using an advanced MRI technique called DTI-ALPS, they measured how well this system was working. Results showed that people with iRBD who had weaker glymphatic function in the left hemisphere were 2.4 times more likely to develop Parkinson’s disease later on.

This finding is particularly striking because Parkinson’s often begins asymmetrically, affecting one side of the body first. This imaging marker could be the earliest known predictor of Parkinson’s in iRBD patients (2^✔ ✔Trusted Source
Association of DTI-ALPS Glymphatic Index With Differential Phenoconversion in Isolated REM Sleep Behavior Disorder: A Multi-Cohort MRI Study

Go to source).

Biomarker Discovery #2: Free Water Levels and Dementia with Lewy Bodies

The second study, published in Alzheimer’s & Dementia, zeroed in on iRBD patients who developed dementia with Lewy bodies. Scientists examined the nucleus basalis of Meynert, a brain region vital for cognition, and measured “free water”- fluid not bound to cells.

They found that higher levels of free water in this region strongly predicted who would later develop DLB. Over an average of 8.4 years of follow-up, those with elevated free water were eight times more likely to develop DLB compared to others (3^✔ ✔Trusted Source
Free water predicts dementia with Lewy bodies in isolated REM sleep behavior disorder

Go to source).

This marker was even more accurate than traditional measures like brain shrinkage, making it a powerful tool for early detection.

Early Detection of Parkinson’s and Dementia Through iRBD Biomarkers

These findings represent a huge leap forward in the world of neurology. For decades, doctors have known that iRBD is a warning sign, but now they can start to differentiate which disease will follow. This opens the door to:

• Personalized monitoring: Doctors can tailor follow-up plans depending on whether Parkinson’s or DLB is more likely.
• Earlier interventions: Identifying risks before symptoms appear means treatments could start at the stage when brain cells are still salvageable.
• Stronger clinical trials: Researchers can recruit the right patients early, improving the chances of testing new preventive therapies successfully.

New Hope for People with iRBD

If you or a loved one has been diagnosed with iRBD, this research offers new hope. While it doesn’t mean a cure yet, it provides:

• Clarity about the type of disease that may follow.
• The possibility of joining clinical trials earlier.
• A chance to adopt brain-protective habits, like regular exercise, balanced diet, quality sleep, and avoiding toxins, to potentially slow disease progression.

Isolated REM sleep behavior disorder is no longer just an unusual sleep condition- it is a critical early alarm system for brain disease. Thanks to advanced imaging biomarkers, doctors can now begin to distinguish whether iRBD will lead to Parkinson’s or dementia with Lewy bodies. This breakthrough not only offers patients valuable foresight but also lays the foundation for earlier treatments and preventive care.

References:

1. Does isolated REM sleep behaviour disorder predict Parkinson’s disease or dementia? - (https://nouvelles.umontreal.ca/en/article/2025/09/23/does-isolated-rem-sleep-behaviour-disorder-predict-parkinson-s-disease-or-dementia)
2. Association of DTI-ALPS Glymphatic Index With Differential Phenoconversion in Isolated REM Sleep Behavior Disorder: A Multi-Cohort MRI Study - (https://pubmed.ncbi.nlm.nih.gov/40956987/)
3. Free water predicts dementia with Lewy bodies in isolated REM sleep behavior disorder - (https://pmc.ncbi.nlm.nih.gov/articles/PMC12447249/)

Source-Medindia