Last Updated: 2008-12-24 16:00:01 -0400 (Reuters Health)

More than half of patients with an idiopathic REM sleep behavior disorder develop a neurodegenerative disease within 12 years of being diagnosed, a Canadian study indicates.

REM sleep behavior disorder is characterized by a loss of muscle atonia that normally occurs during REM sleep, leading to excessive motor activity in association with dream content, Dr. Ronald B. Postuma, at McGill University in Montreal, Quebec, and co-authors explain in the December 24th online issue of Neurology.

Small studies have identified idiopathic REM sleep behavior disorder as a risk factor for Parkinsonism and dementia, the investigators note, but "obtaining an accurate picture of the risk of developing a neurodegenerative disorder is essential for accurate counseling of patients and for planning of any potential neuroprotective trials."

They therefore conducted a follow-up study of 93 patients diagnosed with idiopathic REM sleep behavior disorder between 1989 and 2006.

Mean age of the subjects was 65 years, and 80% were male. The average time between onset of the sleep disorder and diagnosis by polysomnography was 7.2 years, and average time from diagnosis to last evaluation was 5.2 years.

During follow-up, 14 patients developed idiopathic Parkinson’s disease, 7 developed Lewy body dementia, 4 developed Alzheimer’s disease, and 1 developed multiple system atrophy.

"The estimated 5-year risk of neurodegenerative disease was 17.7%," the authors report. "The 10-year risk was 40.6%, and the 12-year risk was 52.4%."

"The results may help us better understand how these neurodegenerative diseases develop," Dr. Postuma commented in a press statement. "They also suggest that there may be an opportunity for protecting against the progression to disease, perhaps even preventing it before the symptoms can appear."

Neurology 2008.