Neurologists often hear, anecdotally, that someone with PD or related neurodegeneration has acted out dreams for years or longer. “We were struck by the lengthy nature of the sleep disorder prior to the development of a neurodegenerative disorder,” Boeve said. The condition affects both men and women, but is more common in men. In fact, wives of patients sometimes report that they first discovered RBD symptoms during their honeymoon. Studies and surveys indicate a wide range of RBD frequencies in the general population, Boeve said, ranging from less than 1 percent to as many as 9 percent of people. Some studies may come up with a lowball number, he noted, because wives are wary to admit the problem for fear their husbands will be prosecuted for battery. Neurologists may sometimes miss the connection, since patients with parkinsonism do not always think to bring up sleep disturbances during an exam.

Boeve and colleagues designed a retrospective study to confirm links between anecdotal reports of long-term RBD and α-synucleinopathies. First author Daniel Claassen, now at the University of Virginia in Charlottesville, searched five years’ worth of Mayo Clinic records for people who had either PD, DLB, multiple system atrophy, or mild cognitive impairment, plus clinically confirmed RBD. Of those 550 people, 27 had RBD stretching back 15 years or more prior to their neurodegeneration diagnosis.

The study extends the time frame between RBD onset and the appearance of neurodegenerative symptoms. “Some of these folks even had the sleep disorder for close to 50 years,” Boeve said. According to the clinical records, the median time between onset of RBD and onset of further degeneration was 25 years, with a range of 15-50 years. RBD started any time between age 21 and age 60, with a median age of onset of 49. The results fit well with a 2009 prospective study, which found that approximately half of people with RBD would develop PD or LBD within 12 years (Postuma et al., 2009).

Boeve suggests there is a slow, creeping process of pathology that hits the brainstem, where important REM sleep circuits are located, before it progresses to the midbrain and cortex, causing waking symptoms. “The pathogenic process may span most of the lifetime,” the authors write.

The data do not necessarily mean that everyone with RBD will develop a neurodegenerative disease, Boeve said, although the risk appears to be high. Risk data are sparse, but Boeve estimated that more than half of people with RBD are at risk for dementia. He and his coauthors also noted the possibility that all RBD patients would develop further illness if they lived long enough.

If this hypothesis is correct, it has important clinical implications, wrote Arvid Rongve, of Haugesund Hospital in Norway, in an e-mail to ARF. The work could mean there is a huge window of time in which to intervene and, hopefully, prevent or delay the cognitive decline associated with α-synucleinopathies. Rongve has collaborated with Boeve on other research.—Amber Dance.

Reference:
Claassen DO, Josephs KA, Ahlskog JE, Silber MH, Tippmann-Peikert M, Boeve BF. REM sleep behavior disorder preceding other aspects of synucleinopathies by up to half a century. Neurology. 2010 Jul 28. Abstract