Canadian researcher finds risk factors for violent sleep disorder

It's rare, but a small group of people have a propensity of turning their bed partners into punching bags.

Now a Canadian researcher has zeroed in on some of the risk factors for REM (rapid eye movement) sleep behaviour disorder, which causes sleepers to act out their dreams, sometimes violently.

A study led by Dr. Ronald Postuma of McGill University, published in the journal Neurology this week, found smoking, pesticide exposure, head injury, farming and less education were risk factors for the disorder.

"People with the disorder ... do not have the normal lack of muscle tone that occurs during rapid eye movement (REM) sleep, causing them to act out their dreams," the American Academy of Neurology said in a news release Wednesday.

"The movements can sometimes be violent, causing injury to the person or their bed partner."

The disorder is thought to occur in less than one-half of one per cent of adults and is more common in men and older people.

"Essentially, all of us normally are paralyzed when we go into our REM sleep," Postuma told The Canadian Press.

"So we're having very vivid dreams, but we don't move. Our eyes will move and we'll breathe, but that's it."

But for sleepers with the disorder, the system that paralyzes them stops working, he said. So whatever a person dreams, they are capable of doing.

"It just looks like they're acting out one-half of the scenario," the Montreal neurologist said.

"So, for instance, they'll be having a conversation and hold up one end of the conversation. They might gesticulate. They might talk articulately. They might laugh, they might cry, they might smile."

It all sounds relatively benign, except if the dream turns violent. The consequences can be painful, even deadly.

In 2009, a British man strangled his wife to death while the couple were camping. He dreamed he and his wife were being attacked and was choking the imagined attacker.

"It was really very tragic," Postuma told The Canadian Press, adding the man was declared not guilty because of his disorder.

[Related: Husband strangles wife after stopping anti-depressants ]

Medication can ease the disorder but those with the most severe cases of the disorder sleep alone to prevent them from harming their partners. However, they can also hurt themselves by throwing themselves out of bed or banging a wall with their fist.

The rarity of the disorder made it hard to gather enough data for a full study, said Postuma, so his team worked with 13 institutions in 10 countries "to get a full picture of the disorder."

The study looked at 347 people with the disorder and compared them with an equal number who did not have it, including 218 with other sleep disorders and 129 who had none.

Of those with REM sleep behaviour disorder, 43 per cent were more likely to be smokers, compared with 56 per cent of those without the disorder. They were also 59 per cent more likely to have suffered a previous head injury that caused them to lose consciousness.

Some 67 per cent were more likely to have worked as farmers and were more than twice as likely as the control group to have been exposed to pesticides through work.

They also had an average 11.1 years of education, compared with 12.7 years for those without the disorder.

Postuma said pesticide exposure was the strongest factor associated with the disorder.

Equally important, this sleep disorder seems to be a precursor to Parkinson's disease and a specific type of dementia, called dementia with Lewy bodies. This connection could aid in early intervention.

"What's going to happen to them is that they're going to have a 50 per cent or more chance of developing one of these very serious disorders over the next 10 to 15 years," Postuma told The Canadian Press.

"So this gives you a window. You can move 10 or 15 years earlier and look at the risk factors."

The study appears to buttress conclusions of another study earlier this year that showed elderly people who act out their dreams have twice the risk of developing Parkinson's or mild cognitive impairment — considered an early sign of dementia — in the following four years.

Dr. Brendon Boot, a neurologist at Boston's Brigham and Women's Hospital, who co-authored that study, suggested those who act out their dreams should consult a neurologist or sleep-disorder specialist, since other disorders can produce similar symptoms.