Prodromal PD and RBD: What Is the Link?
When we think of Parkinson’s disease, the first image that generally comes to mind is that of a person shaking, or perhaps walking slowly with a stooped posture. Although the motor manifestations of Parkinson’s (slowness of movement, rigidity, tremor, etc.) are still the core features by which a diagnosis is made, there is much more to Parkinson’s that this. Non-motor features, including sleep disturbances, autonomic changes (constipation, bladder and blood pressure changes, etc.), cognitive changes, anxiety, and many more symptoms are common in Parkinson’s disease.
Whereas recognizing and treating non-motor features is critical to ease the burden of Parkinson’s, there is more to the story. We now know that these non-motor features are often the earliest symptoms, starting years or even decades before Parkinson’s is diagnosed. For example, people can lose their sense of smell 20 years before diagnosis, might start to develop constipation, bladder changes, and blood pressure changes 10-25 years before, or can start to have changes in thinking, mood or anxiety levels anywhere from 2-20 years before.
The ability of catching Parkinson’s at its early stages is obviously very intriguing. However, it may eventually have important treatment implications as well. If we are able to identify Parkinson’s earlier, then there may eventually be a possibility to intervene earlier, to change the course of Parkinson’s progression. However, a major problem is that most of our predictive features are not specific. For example, whereas constipation approximately doubles the chance of Parkinson’s in the future, this still implies that well over 90% of people who experience constipation will never get Parkinson’s at all.
There is a condition, however, that is different, and this is REM sleep behavior disorder (RBD). RBD is caused by loss of a normal a system that keeps us paralyzed during our REM sleep stage (when dreams are most vivid) – this system prevents us from moving during our dreams. In RBD, when the system breaks down, people will ‘act out’ their dreams (talking loudly, singing, making running movements, punching, etc.) This is different than the common sleep walking or sleep talking of children and young adults; it’s something that generally starts as people age (50’s and older). Over the last decade or so, we have learned that the large majority of those with RBD are actually in early stages of Parkinson’s or other closely related conditions (namely Dementia with Lewy bodies or Multiple System Atrophy). It is, in fact, the Parkinson’s degeneration itself that is causing the system to break down. The predictive ‘specificity’ is so strong that if someone has RBD, the chance of being diagnosed with Parkinson’s or related conditions over the next 15 years or more is over 80%.
Researchers have begun to intensely study those with RBD, in order to learn more about the early stages of Parkinson’s. By looking closely at those with RBD, we can start to understand what other factors can predict Parkinson’s disease. We can see how Parkinson’s evolves over time to understand what symptoms appear in which order. We can test other potential diagnostic tests for Parkinson’s such as tissue biopsy, samples of blood or cerebrospinal fluid, or neuroimaging scans, to see how reliably and early these tests can diagnose Parkinson’s. We can start to identify exactly when people will ‘convert’ to a full Parkinson or cognitive syndrome. Finally, and most importantly, we can start to get ready for preventative treatment. Any treatment that slows the progression of Parkinson’s disease will be an amazing development. By studying those with RBD, we can test potential treatments at the earliest stages, when intervening has the most chance of success.
If you know someone who ‘acts out’ their dreams but who does not have a diagnosis of Parkinson’s or related condition, there may be opportunities to participate. Groups like the international RBD study group, the North American Prodromal Synucleinopathy group and the Michael J Fox foundation are actively working in this area, and are happy to help get you connected.
Ron Postuma, MD, MSc, has presented at many past World Parkinson Congresses. He is currently a clinical researcher and movement disorders neurologist at Montreal Neurological Institute-Hospital where he treats people with Parkinson's disease and related disorders. His research interest focuses on Parkinson’s, particularly on detecting early stages of disease, examining the impact of non-motor symptoms on disease subtype and prognosis, and testing new treatments for non-motor manifestations such as sleep disorders.
Ideas and opinions expressed in this post reflect that of the author solely. They do not reflect the opinions or positions of the World Parkinson Coalition®