Rare sleep disorder that causes violent kicking and punching tied to smoking, pesticides

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(CBS News) A rare sleep disorder in which people violently kick, punch or thrash in their sleep may be more common in smokers and people heavily exposed to pesticides, new research suggests.

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The sleep-kicking disorder is actually called "REM sleep behavior disorder." According to WebMD, people typically lose muscle tone (paralysis) during the rapid eye movement (REM) stage of sleep - but that doesn't occur in people with the disorder, causing them movements (sometimes violent) that can seriously harm the individual or their sleep partner. It is estimated to affect only 0.5 percent of adults.

"Until now, we didn't know much about the risk factors for this disorder, except that it was more common in men and in older people," study author Dr. Ronald B. Postuma, a sleep researcher at the Research Institute of the McGill University Health Centre (MUHC) in Montreal, said in a press release. "Because it is a rare disorder, it was difficult to gather information about enough patients for a full study. For this study, we worked with 13 institutions in 10 countries to get a full picture of the disorder."

The study, published in the June 27 issue of Neurology, involved 347 people who had the disorder and another 347 people who didn't. A closer look found people with the disorder were 43 percent more likely to be smokers. Other risk factors that emerged for people with the disorder were that they were 59 percent more likely to have had a previous head injury that caused a loss of consciousness. Sixty-seven percent were more likely to have worked as a farmer and more than twice as likely to have been exposed to pesticides through work. People with the disorder also had on average a year and a half less of education. The study didn't find a cause-and-effect link between these risks, only an association.

WebMD reports that 55 percent of people with the disorder have it from unknown causes, while 45 percent of cases are linked to withdrawal from alcohol or sedatives or antidepressants. The disorder may also occur in association with other neurological diseases such as Parkinson's disease, but REM sleep behavior disorder often starts years before patients are diagnosed with other neurological conditions.

Dr. Shelby Freedman Harris, director of the behavioral sleep medicine program at Montefiore Medical Center in New York City, told HealthDay the condition can be treated by a neurologist with medication such as the muscle relaxer clonazepam (Klonopin) and with changes to the sleep environment that reduce the risk of injury.

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