A little-known and poorly understood sleep disorder that occurs during the rapid eye movement, or REM, stage of sleep has garnered attention for its role in foreshadowing neurodegenerative brain diseases such as Parkinson’s disease and Lewy body dementia. The disorder, known as REM sleep behavior disorder, or RBD in the medical field, affects around 1 percent of the general population worldwide and about 2 percent of adults over 65.
The Conversation talked with Dr. Anelyssa D’Abreu, a neurologist specializing in geriatric neurology, to discover what researchers know about the condition’s links to dementia.
1. What Is REM Sleep Behavior Disorder?
Every night, you go through four to five sleep cycles. Each cycle, lasting about 90 to 110 minutes, has four stages. That fourth stage is REM sleep.
REM sleep only comprises 20 to 25 percent of total sleep, but its proportion increases throughout the night. During REM sleep, your brain rhythms are similar to when you are awake; your muscles lose tone, so you cannot move, and your eyes, while closed, move quickly. Muscle twitches and fluctuations in your respiratory rate and blood pressure often accompany this stage.
But someone with REM sleep behavior disorder will act out their dreams. For poorly understood reasons, the dream content is usually violent—patients report being chased or defending themselves, and as they sleep, they shout, moan, scream, kick, punch, and thrash about.
Injuries often result from these incidents; patients may fall from bed or accidentally harm a partner. Some 60 percent of patients and 20 percent of bed partners of people with this disorder sustain an injury during sleep.
Appropriate testing, including a sleep study, is needed to determine if a patient has REM sleep behavior disorder, as opposed to another disorder, such as obstructive sleep apnea. This is a disorder in which breathing is interrupted during sleep.
REM sleep behavior disorder can occur at any age, but symptoms usually start in people in their 40s and 50s. For those younger than 40, antidepressants are the most common cause of REM sleep behavior disorder; in these younger patients, the disorder affects both sexes about equally, but past age 50, it’s more common in males.
2. What Causes REM Sleep Behavior Disorder?
The disease mechanism is not well understood. In some cases of RBD, a clear cause cannot be identified. In other cases, the disorder may be caused by something specific, such as obstructive sleep apnea, narcolepsy, psychiatric disorders, use of antidepressants, autoimmune disorders, and brain lesions, which are areas of damaged brain tissue.
In both situations, RBD may be associated with synucleinopathies, a group of neurodegenerative disorders in which aggregates of the protein alpha-synuclein accumulate in brain cells. The most common of these neurodegenerative disorders is Parkinson’s disease. Others are dementia with Lewy bodies, multiple system atrophy, and pure autonomic failure. RBD may precede these diseases or occur at any time during the disease process.
3. What Are the Links Between the Sleep Disorder and Dementia?
RBD may be the first symptom of Parkinson’s disease or dementia with Lewy bodies. It is observed in 25 to 58 percent of patients diagnosed with Parkinson’s, 70 to 80 percent of patients with Lewy body dementia, and 90 to 100 percent of those with multiple system atrophy.
In a long-term study of 1,280 patients with RBD who didn’t have Parkinsonism—an umbrella term that refers to brain conditions, including Parkinson’s disease, that cause slowed movements, stiffness, and tremors—or dementia, researchers followed participants to find out how many would develop these disorders. After 12 years, 73.5 percent of those with RBD had developed a related neurodegenerative disorder.
Some factors that independently increased the risk of developing a neurodegenerative disorder were irregular motor symptoms, abnormal dopamine levels, loss of sense of smell, cognitive impairment, abnormal color vision, erectile dysfunction, constipation, and older age.
RBD may also be observed in other neurodegenerative disorders, such as Alzheimer’s and Huntington’s disease, but at much lower rates. The association is also not as strong as that observed in the synucleinopathies.
4. Does an Early Diagnosis Help?
For most neurodegenerative disorders, there is a phase that may last for decades in which brain changes are taking place, but the patient either remains asymptomatic or develops symptoms without the full expression of the disease. RBD, in that scenario, is an early sign of those disorders. Therefore, this provides an opportunity to study how the disease progresses in the brain and to develop therapies that could either slow this process or prevent it from happening.
Currently, there are no approved therapies to prevent the onset of these neurodegenerative diseases in those with RBD. There are, however, medications such as melatonin and clonazepam that may improve the symptoms. We also recommend measures to avoid injury, such as removing breakable objects from the room, protecting windows, and padding floors.
Patients who are affected by RBD may choose to participate in research. Proper treatment of the disease can help prevent injury and improve quality of life.