“Kicking and lashing out while asleep could mean you’re more likely to develop dementia or Parkinson’s disease,” reported the Daily Mail . It said a study has found a link between a sleep disorder and a higher risk of certain types of dementia up to 50 years later.
The study looked at people diagnosed with one of several related neurological conditions and analysed their history of a severe form of REM sleep behaviour disorder (RBD), a condition in which people can act out recurrent dreams and move excessively while asleep.
The study was not designed to look at the strength of the link between RBD and dementias, as patients in the study were selected because they were known to have had both of these conditions. Therefore, it is not possible to say from this study whether restless sleep is a predictor of future dementia as is implied in the newspaper headline. More research into whether RBD could be an early sign of the brain changes that lead to dementia later on would be useful.
Where did the story come from?
The study was carried out by researchers from the Department of Neurology at the Mayo Clinic in the US. The researchers received several individual grants and awards. The study was published in the peer-reviewed medical journal Neurology .
The Daily Mail has concentrated on the theoretical link between a group of neurological conditions and this sleep disorder. Previous research has indicated that there is some association between the two, but the strength of this relationship is unclear and, at this stage, RBD cannot be used to predict later disease.
What kind of research was this?
The stage of sleep in which your brain activity increases and when dreaming may occur is known as rapid eye movement (REM) sleep because, during this phase, your eyes start to move quickly and flicker.
This research looked at the association between a sleep disorder called REM sleep behaviour disorder (RBD) and a group of neurological conditions including Parkinson’s disease, multiple system atrophy (MSA) and dementia with Lewy bodies (DLB). RBD is a sleep disorder where people act out recurrent dreams and move excessively while asleep, and in this study injured themselves or their partners as a result.
To investigate this, the researchers used the records from a specialist neurological clinic of 27 patients who had been diagnosed with RBD and then went on to develop degenerative neurological symptoms at least 15 years later.
The researchers confirmed the diagnoses of RBD and analysed the records to define the types and timing of diseases and symptoms the patient developed. They used these data to calculate the length of time between the first sign of restless sleep and the diagnosis of a range of dementias.
This was a case series analysis in which all the participants were selected because they had both conditions. As such, it cannot demonstrate a link between the conditions as there was no comparison group. However, the researchers refer to previous research that they say has demonstrated this link. They say that the first study to document this relationship reported that nearly 40% of patients with isolated, idiopathic RBD developed a parkinsonian disorder an average of 12.7 years later. This current study was mainly interested in the question of whether the length of time between RBD and dementia could be even longer than 12.7 years.
What did the research involve?
Some patients with these neurological disorders have reported that their first experience of restless sleep happened many years previously. The aim of this study was to explore a theory based on this anecdotal evidence that RBD symptoms can predate Parkinson’s disease by several decades.
The researchers were interested in a range of conditions thought to be caused by abnormal deposition of a protein called alpha-synuclein in the brain. These diseases included Parkinson's disease, dementia with Lewy bodies and multiple system atrophy, which are all neurodegenerative diseases that appear later in life.
The researchers used the Mayo Clinic’s records to identify all patients who had been evaluated for these diseases between 2002 and 2006. They then selected all those who had a history of RBD and for whom there was at least 15 years between onset of RBD and their neurodegenerative symptoms. To be eligible, patients also had to have been assessed by a specialist in a sleep lab and by at least one other neurological specialist in the Mayo Clinic’s behavioural neurology or movement disorders sections.
RBD was diagnosed if abnormal flailing movements occurred during sleep, with sleep-related injuries or movements that were potentially injurious or disruptive. Symptoms of physical activity during sleep were provided by the patient and bed partner. Patients were then divided into probable and definite RBD. The numbers of patients with the different disorders were counted, and the interval between RBD and symptom onset for the neurological disorder recorded.
What were the basic results?
The researchers identified 550 patients with RBD and one of the three neurodegenerative disorders of interest.
Of the 550 patients, 27 (4.9%) had first started experiencing RBD more than 15 years before the onset of neurodegenerative disease symptoms. Of these, 13 had developed Parkinson’s disease, Parkinson’s with mild cognitive impairment or Parkinson disease dementia. Another 13 had developed probable dementia with Lewy bodies and one had developed parkinsonism-predominant MSA.
Most of the patients were male (24 [89%]). The average (median) interval between RBD symptoms and neurodegenerative syndrome symptom onset was 25 years (range 15–50 years), and the median age at onset of restless sleep was 49 years.
How did the researchers interpret the results?
The researchers say that their cases add a new time dimension to theories on the evolution of neurodegenerative syndromes characterised by alpha-synuclein deposition. They say that, until now, the estimated interval between changes in the brain and disease onset had been about 5-6 years, but this study suggests that it may be longer.
These findings suggest that the brain changes associated with certain neurodegenerative diseases could begin many years before the symptoms start to show.
There are a few points to note about this study:
- This study was not set up to evaluate the strength of the association between RBD and neurodegenerative disease, and it does not shed any light on how many people with restless sleep go on to develop neurological conditions.
- The study only looked at a few specific types of dementia and not the more common Alzheimer’s or vascular type of dementia. As such, these findings are even less applicable to people concerned about the more common dementias.
- These participants had a very specific form of severe sleep disturbance, involving lashing out and characteristic brain wave patterns during their sleep. Many people will have the occasional restless night of sleep, but most are unlikely to have RBD. The results of this study are unlikely to apply to them.
In general, this study provides some insight into these rare conditions and will be of interest to doctors, scientists and the public. The results should not be interpreted to mean that restless sleep can be used to predict future dementias or neurological diseases.