NEW YORK (Reuters Health) – REM sleep behavior disorder is associated with a ìsubstantialî risk for eventual development of neurodegenerative diseases such as Parkinson disease and Lewy body dementia, according to a report from Canada.

Patients with REM sleep behavior disorder (RBD) have excessive motor activity — for example, punching, kicking, or crying out — while dreaming, explain the authors of the report, which appears in the April 14th issue of Neurology.

Led by Dr. Ronald B. Postuma at the Montreal General Hospital, the researchers conducted a follow-up study of 93 patients diagnosed with idiopathic RBD between 1989 and 2006.

"Over the follow-up period, 26/93 patients developed a neurodegenerative disorder," the authors write. Parkinson disease developed in 14 of the 26 patients, Lewy body dementia in seven, Alzheimer’s disease in four, and "multiple system atrophy" in one patient.

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

The researchers found no significant differences in age, gender, or duration of RBD between patients who did or did not develop neurodegenerative disease, but they noted that the risk of dementia might have tended to be lower in women.

In fact, patientsí risk of neurodegenerative disease was actually "somewhat lower than found in two previous case series," the authors said. The difference, they suggest, might be explained by their stricter neurodegenerative disease definitions, which excluded patients with mild cognitive impairment and patients with only mild signs or a single cardinal manifestation of parkinsonism.

In an editorial, Dr. Thomas C. Britton and Dr. K. Ray Chaudhuri, both at Kingís College Hospital in London, UK, ask, "So what should we tell our patients who are given a diagnosis of idiopathic RBD? There is a significantly increased risk of developing parkinsonism or dementia over a 10-year period, although progression to a neurodegenerative disease is not (as far as we can tell so far) inevitable."

"It is still too early to say whether idiopathic RBD will be a useful preclinical marker for future neuroprotective therapies, but this may change as our understanding of the neurodegenerative diseases, particularly the alpha-synucleinopathies, improves and with longer follow-up of patients with idiopathic RBD," the editorialists continue. Such follow-up, they note, "is required over decades."

Reference:
Neurology 2009;72:1294-1300.