A new study shows that a sleep disorder may be a sign of dementia or Parkinson's disease up to 50 years before the conditions are diagnosed. The research is published in the July 28, 2010, online issue of Neurology, the medical journal of the American Academy of Neurology.

Using Mayo Clinic records, researchers identified 27 people who experienced rapid eye movement (REM) sleep behavior disorder for at least 15 years before developing one of three conditions: Parkinson's disease, dementia with Lewy bodies, or multiple system atrophy. Multiple system atrophy is a disorder that causes symptoms similar to those of Parkinson's disease. People with REM sleep behavior disorder often act out their dreams with violent movements, such as punching, which can injure themselves or bed partners.

The study found that the time between the start of the sleep disorder and the symptoms of the neurologic disorders ranged up to 50 years, with an average span of 25 years. Of the participants, 13 were diagnosed with dementia, 13 others were diagnosed with Parkinson's disease, and one person was diagnosed with multiple system atrophy.

"Our findings suggest that in some patients, conditions such as Parkinson's disease or dementia with Lewy bodies have a very long span of activity within the brain and they also may have a long period of time where other symptoms aren't apparent," said study author Bradley F. Boeve, MD, with the Mayo Clinic in Rochester, Minn, and a member of the American Academy of Neurology. "More research is needed on this possible link so that scientists may be able to develop therapies that would slow down or stop the progression of these disorders years before the symptoms of Parkinson's disease or dementia appear."

It is not known how many people who experience REM disorder may develop diseases such as Parkinson's or dementia. A corresponding editorial noted there is no evidence that narcolepsy, with or without REM disorder, will later lead to neurodegenerative disorders.

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