Violent dreams may predict illness in advance

Sleep disorder can precede neurodegenerative disease by decades

Vivid, violent dreams can portend brain disorders by half a century, a new study finds. The result, reported in the Aug. 10 Neurology, highlights how some neurological diseases may take hold decades before a person is diagnosed. Spotting early warning signs of the disease may allow clinicians to monitor and treat patients long before the brain deteriorates.

People with a mysterious sleep disturbance called REM sleep behavior disorder, or RBD, experience a sudden change in the nature of dreams. Dreams increasingly become more violent and frequently involve episodes in which an attacker must be fought off. The normal muscle paralysis that accompanies dreams is gone, leaving the dreamer, who is most often male, to act out the dream’s punches, twists and yells. In many cases, a person sharing the dreamer’s bed can be injured.

Doctors used to think of RBD as an isolated disorder. But follow-up studies revealed that a striking number of these patients later develop neurodegenerative diseases, including Parkinson’s disease and Lewy body dementia. The exact figures vary, but some studies find that anywhere from 80 to 100 percent eventually get a neurodegenerative disorder.

“The consensus among all RBD researchers is that it’s not a matter of if, but when,” says sleep expert Carlos Schenck of the Minnesota Regional Sleep Disorders Center in Minneapolis, who was one of the first researchers to describe RBD. “Basically, the longer you follow these men, the more they will convert to a neurodegenerative disorder.”

In the new study, neurologist Bradley Boeve of the Mayo Clinic in Rochester, Minn., and his colleagues wanted to know just how long the interval between RBD and a neurodegenerative disorder can be. “Everybody who sees patients with this knew it could go on for a long time,” Boeve says, but nobody knew just how long.

Boeve and his team examined medical records of patients from the Mayo Clinic to identify people diagnosed first with RBD and then with a neurodegenerative disorder at least 15 years later.

Of the 27 patients who fit the criteria (of which only three were women, reflecting the curious male predominance of RBD), the median interval between onset of the sleep disorder and of the neurological disorder was 25 years, the team found. For six of these patients, Boeve says, the sleep disorder was first noticed by their spouse on their honeymoon or shortly afterward. In one case, RBD preceded Parkinson’s disease by 50 years.

The researchers can’t estimate how frequently this happens in the general population, because patients were selected to have a minimum interval of 15 years between the onset of RBD and diagnosis of neurodegenerative disease. But finding such long intervals between diseases was unexpected.

“In the neurodegenerative realm, we just don’t know any other clinical manifestations that can start so far in advance,” Boeve says. “There are so few other illnesses that can have a window of decades from one clinical manifestation to another.”

The 50-year interval uncovered in the study is an “extraordinarily long and slow lag period,” Schenck says. “That’s the big news.”

Such a long interval brings the hope that once a “mysterious and magical neuroprotective agent is identified,” Schenck says, it could be used before the brain is damaged severely. Some researchers think that by the time dementia symptoms appear, it is already too late to undo the damage.

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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