Smoking and pesticide exposure appear to be strong risk factors for a rare disorder that causes people to physically act out their dreams while asleep, even to the extent of punching and kicking their bedmates, Canadian research suggests.
Individuals with REM sleep behaviour disorder do not exhibit the lack of muscle tone – called atonia – that usually occurs during sleep, leaving them able to move freely.
“Essentially, all of us normally are paralyzed when we go into our REM sleep,” said Dr. Ron Postuma, a neurologist at McGill University who led the international study. “So we’re having very vivid dreams, but we don’t move. Our eyes will move and we’ll breathe, but that’s it.”
In people with the disorder, the body system that keeps sleepers paralyzed stops working, so whatever a person dreams, they are capable of doing.
“It just looks like they’re acting out one half of the scenario,” Postuma said from Montreal. “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.
“If they dream they’re smoking a cigarette, the hand will go up to the mouth and they’ll make puffing motions. Essentially, they’re pantomiming a play that’s going on in their head, and that play is the dream.”
But violent dreams can have nasty consequences: people with the disorder can unknowingly punch, kick and even throttle their bed partners.
A few years ago, a British man strangled his wife while the couple were camping. Falling asleep with the sound of people in the campground “yelling and screaming,” the man dreamed he and his wife were being attacked, and in his sleep state he tried to defend her by choking an imagined attacker.
“It was really very tragic,” said Postuma, explaining that the man was declared innocent because of his disorder.
With severe cases, most patients sleep alone to pre-vent harm to their partners, he said. But patients can also hurt themselves: they don’t walk but can hurl themselves out of bed or bash the wall and break a hand, for instance.
Medications can significantly ease the disorder, which affects less than one per cent of the population and is more common in men than in women and older people. In their study of almost 350 people with the disorder and the same number of control subjects with-out the disorder, researchers found that those with the disorder were 43 per cent more likely to be smokers, with 64 per cent having smoked at one time, compared to 56 per cent of those without the disorder.
The study, published in this week’s issue of the journal Neurology, also found subjects with the disorder were 59 per cent more likely to have had a previous head injury with loss of consciousness.
Two-thirds were more likely to have worked as farmers, and were more than twice as likely to have been exposed to pesticides.
“That was the strongest one, in fact. Pesticides are very clearly associated with REM sleep disorder behaviours,” Postuma said.
But the most important aspect of the disorder isn’t the disorder itself, but the fact it appears to be a possible precursor to Parkinson’s disease and one type of dementia.
“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,” he said.al