People who yell, thrash, punch and kick, and even get out of bed and run around while they're asleep may be at an increased risk for developing neurodegenerative disorders such as Parkinson's disease.

A new study shows that brain imaging techniques may be able to predict which patients with a sleep disorder, called rapid-eye-movement sleep behavior disorder (IRBD), go on to develop neurodegenerative diseases.

In most people, the muscles are essentially paralyzed during REM sleep (the dream stage of sleep), but in people with IRBD, muscles move in response to signals from the brain, so they're active during sleep.

Previous research has shown that IRBD could be an early predictor of neurodegenerative disorders such as Parkinson's disease. However, which patients with IRBD will later develop disorders is not known. Being able to identify them would help scientists better understand how the disease progresses during early stages, and could be an opportunity to treat patients still in those early stages.

Researchers theorized that abnormalities in the brain typical of early Parkinson's disease visible with brain imaging might also occur in some patients with IBRD, and could be used to identify patients who might then be at increased risk of developing a degenerative brain disorder in the short term.

In the study, 43 patients with IRBD were given the brain imaging tests at the start, and then they were assessed for neurodegenerative disorders 2.5 years later.

Twenty-seven patients (63 percent), had abnormal imaging results at the study start. One test showed problems with the transport of dopamine, a chemical that helps control muscle movement, in a part of the brain affected by Parkinson's disease.

Of the patients with abnormal results, eight (30 percent) later developed a neurodegenerative disease. Five developed Parkinson's disease, two developed dementia, and one had multiple system atrophy (a rare disorder that affects movement, balance, and other body functions such as bladder control). Patients with normal brain imaging results at the start of the study remained disease free.

These findings, the authors say, show that brain imaging techniques make it possible to identify neurodegenerative diseases at early stages in patients with REM sleep disturbances.

The study was conducted by an international team of scientists, led by Alex Iranzo de Riquer from the Hospital Clinic of Barcelona, Spain.

The article will be published online in the October edition of The Lancet Neurology.