People with symptoms suggesting rapid eye movement sleep behavior disorder, or RBD, have twice the risk of developing mild cognitive impairment (MCI) or Parkinson's disease within four years of diagnosis with the sleep problem, compared with people without the disorder, a Mayo Clinic study has found.

The researchers published their findings recently in the Annals of Neurology.

One of the hallmarks of rapid eye movement (REM) sleep is a state of paralysis. In contrast, people with rapid eye movement sleep behavior disorder, appear to act out their dreams when they are in REM sleep. Researchers used the Mayo Sleep Questionnaire to diagnose probable RBD in people who were otherwise neurologically normal. Approximately 34 percent of people diagnosed with probable RBD developed MCI or Parkinson's disease within four years of entering the study, a rate 2.2 times greater than those with normal rapid eye movement sleep.

"Understanding that certain patients are at greater risk for MCI or Parkinson's disease will allow for early intervention, which is vital in the case of such disorders that destroy brain cells. Although we are still searching for effective treatments, our best chance of success is to identify and treat these disorders early, before cell death," says co-author Brad Boeve, M.D., a Mayo Clinic neurologist.

Previous studies of Mayo Clinic patients have shown that an estimated 45 percent of people who suffer from RBD will develop a neurodegenerative syndrome such as mild cognitive impairment or Parkinson's disease within five years of diagnosis.

RBD, MCI and Parkinson's Disease

"This study is the first to quantify the risk associated with probable RBD in average people, not clinical patients, and it shows that we can predict the onset of some neurodegenerative disorders simply by asking a few critical questions," says lead author Brendon P. Boot, M.D., a behavioral neurologist. Dr. Boot was at Mayo Clinic when the study was conducted. He is now at Harvard University.