Melvin Abel could see that the deer he’d just clobbered with a pitchfork wasn’t quite dead.
Wanting to put the animal out of its misery, the 70-year-old retired real estate agent grabbed the doe’s neck to snap it — and was woken by his wife, Harriet, screaming at him to stop.
The deer episode was only a dream, but his hands gripping his wife’s head and neck were very real.
This dramatic scene unfolded because Mr Abel had rapid eye movement (REM) sleep behaviour disorder, a condition characterised by acting out dreams — sometimes violently.
It affects as many as 1 in 100 middle-aged and older people, according to a 2017 Swiss survey.
Afflicted people can hurt themselves, as well as anyone sharing their bed, but the condition is also linked to developing Parkinson’s disease and related dementias down the track.
Not just an older man’s condition
In the early 1980s, when Mr Abel almost killed his wife in his sleep, REM sleep behaviour disorder — or RBD — wasn’t yet a recognised and diagnosable condition.
After the deer dream debacle, he visited a sleep disorder centre in Minnesota, where he met psychiatrist Carlos Schenck.
“When Mel recollected [the incident], he was crying and breaking down,” Professor Schenck, now at the University of Minnesota, recalled.
Mr Abel was the second patient Professor Schenck saw who displayed aggressive behaviour while sleeping, often trying to “act out” whatever they were dreaming about at the time.
Other patients showed up at the centre after they dove off the bed, kicked and punched their partner or rammed into furniture while dreaming they were being chased, under attack or playing football.
During their waking hours, they were usually kind, mild-mannered people. Violence was very out of character.
In 1986, Professor Schenck and his colleagues formally described RBD.
It’s often thought of as a disorder that mostly strikes older men, usually because they inflict more damage, but men and women are equally affected.
RBD is an entirely different beast to sleepwalking or night terrors, which tend to happen during non-REM sleep, said Ron Grunstein, a sleep physician at Sydney’s Woolcock Institute.
“They typically occur in the beginning of sleep, the first couple of hours,” Professor Grunstein said.
“RBD is predominant when there’s REM sleep, which is usually the second half of the night.”
He’s only part-time in the clinic, but sees around 25 new RBD patients each year, most of whom have had symptoms for a long time.
“It really only comes to attention because they’ve read something about it online or it’s become worse, and they pushed their GP for a referral.”
Links to Parkinson’s and dementias
Professor Schenck and his team tracked their patients over the decades following diagnosis — and within a few years, a pattern emerged.
People with RBD were more to develop a neurodegenerative disorder than not.
In a 2013 follow-up study, the researchers reported 13 of 26 patients developed Parkinson’s disease. Another eight from that cohort were living with a related dementia.
This and other research eventually led to RBD being used today as a predictor of Parkinson’s disease.
“If you get RBD, you’re basically 120 times more likely to develop Parkinson’s disease or related conditions than someone who doesn’t have RBD,” Professor Grunstein said.
“It’s a very powerful predictor of that group of disorders.”
So what’s going on in the RBD brain — and why the Parkinson’s link?
In normal REM sleep, the muscles that produce body movement, called skeletal muscle, are paralysed by brain cells in the brain stem.
This paralysis is called “REM atonia”.
But for those with RBD, atonia is switched off and they’re free to flail around — at least part of the time.
The culprit? A wavy molecule called alpha-synuclein found in the brain.
Being a protein, alpha-synuclein must be folded a certain way to work correctly.
But when that folding goes awry, the protein forms toxic clumps that damage cells.
And it just so happens that brain cells responsible for REM atonia are among the first affected.
As time wears on, alpha-synuclein clumps wreak havoc in other parts of the brain, which can lead to Parkinson’s disease, some kinds of dementias and other disorders.
“RBD is really one of the first or earliest signals that the parkinsonian process has begun,” Professor Schenck said.
Early Parkinson’s diagnosis
Not everyone who has Parkinson’s disease experiences RBD, and not all RBD patients will develop Parkinson’s.
And so far, studies have focused on people aged over 50 years.
There’s not yet enough data yet to say if someone under 50 years with RBD will have higher risk of Parkinson’s disease, Professor Schenck said, but sleep researchers will hopefully have some idea within the next five or 10 years.
For older people, though, RBD — along with other early Parkinson’s symptoms — can be used to nail down when the disease will emerge.
At the moment, no therapy can effectively stave off Parkinson’s disease.
But should a treatment be discovered, “identifying RBD early could be crucial”, Professor Grunstein said.
Still, if you — or your partner — tend to lash out while sleeping, it’s a good idea to get to a doctor.
“RBD is treatable with either bedtime melatonin at high doses or clonazepam, or both,” Professor Schenck said.
“Those are very effective medications to control abnormal behaviours and violence.”
In the meantime, separate beds could help too.
Harriet Abel, unsurprisingly, generally slept in another bed after her husband’s deer dream.