People with a sleep disorder that causes them to kick or cry out during their sleep may be at greater risk of developing dementia or Parkinson’s disease, according to a study published in Neurology. 

The sleep disorder is called REM sleep behavior disorder. People with the disorder do not have the normal lack of muscle tone that occurs during REM sleep, often known as the dream stage of sleep. Instead, they have excessive muscle activity such as punching, kicking, or crying out, essentially acting out their dreams. 

The study involved 93 people with this type of sleep disorder who had no signs of a neurodegenerative disease, such as dementia or Parkinson’s disease. The participants were followed for an average of five years. During that time, 26 of the people developed a neurodegenerative disease. Fourteen developed Parkinson’s disease, 11 developed dementia and were diagnosed with either Alzheimer’s disease or Lewy body dementia. One person developed multiple system atrophy, a rare disorder that affects movement, blood pressure and other body functions. 

The estimated five-year risk of developing a neurodegenerative disease was 18 percent, with the 10-year risk at 41 percent and the 12-year risk at 52 percent. 

“These results are obviously of great interest to people who have this sleep disorder and their physicians and families,” said study author Ronald B. Postuma, MD of McGill University in Montreal, Canada, who carried out the studies at the sleep disorders center at the Sacre Coeur hospital, University of Montreal. Postuma is also a member of the American Academy of Neurology. “The results may help us better understand how these neurodegenerative diseases develop. They also suggest that there may be an opportunity for protecting against the progression to disease, perhaps even preventing it before the symptoms can appear.”

Postuma noted that the study involved only people with no known cause for the REM sleep behavior disorder. The disorder can also be caused by narcolepsy or rare brainstem abnormalities. REM sleep disorder from these causes does not necessarily carry the risk of developing a neurodegenerative disease, he said. 

The study was supported by grants from the Canadian Institutes of Health Research and the FRSQ (Fonds de la recherché en santé du Quebec) in Montreal, Canada.