Sweet Dreams Are Made Of This: Could REM Sleep Behaviour Disorder Be A Precursor To Dementia With Lewy Bodies?

Dementia, in its many forms, is an interesting disorder; it comes with quite a variety of impairments and abnormal functioning. Thus, it is not uncommon to find dementia patients suffering from sleep abnormalities. These can manifest as changes in sleep patterns or difficulties in sleeping. There is not a huge amount of knowledge on the reasons behind this, but it is assumed that dementia’s morphing of the brain has an impact on the regions that engage in sleep behaviours. This blog will be focusing specifically on Dementia with Lewy Bodies (DLB) and it’s association with REM Sleep Behaviour Disorder (RSBD).

Dementia with Lewy Bodies counts for approximately 5-10% of all dementia cases; however, it has been suggested that DLB is largely under-diagnosed or misdiagnosed, due to an overlap of features with Alzheimer’s Disease. It’s main symptoms are cognitive fluctuations, hallucinations, disturbed sleep patterns and parkinsonism features (due to its similarities in pathology with Parkinson’s Disease). It can be identified at autopsy by the large number of lewy bodies found in the limbic system, basal ganglia and cortex. Lewy bodies are abnormal aggregates of protein found inside neurons. For more information on DLB, please see: http://www.alzheimers.org.uk/site/scripts/documents_info.php?documentID=113.

REM Sleep Behaviour Disorder has been commonly associated with DLB and other disorders that occur with the presence of synucleinopathies. A review paper by Turner (2002) report that out of 93 cases of Parkinson’s Disease, Multiple Systems Atrophy and DLB, 86% of patients were found to suffer from RSBD. But what is RSBD? There are three stages of the wake-sleep cycle: wakefulness, REM sleep and non-REM sleep. REM sleep is the lightest stage of sleep, characterized by rapid eye movements, paralysis of muscles and dreaming. RSBD appears to reflect a dysfunction in this stage of sleep, with loss of muscle atonia and vivid dreams (Boeve , Silber & Ferman, 2004). It is characterized by abnormal vocalizations, such as yelling or swearing, and abnormal motor behaviour, which can be simple jerky movements or limb flailing, punching, etc.  Patients usually report dreams to involve insects or animals, and being chased or attacked. Bed partners’ comments or attempts to wake up the patient may become interwoven into the dream, and lead to harm of the patient or partner. The frequency and severity of the dream re-enactment usually wanes as the dementia progresses. Below, I have linked a video that provides a brief glimpse at how RSBD may manifest itself:

How can REM Sleep Behaviour Disorder help with the diagnosis of Dementia with Lewy Bodies?

It has been indicated that RBD is a supportive feature in the diagnosis of DLB as it occurs when there is a greater frequency of synucleinopathies than in other disorders, such as Alzheimers Disease or Fronto Temporal Dementia (Boeve, 2010). Synucleinopathies are abnormal aggregates of alpha-synuclein proteins in nerves, glial cells or nerve fibres, i.e. Lewy bodies. Boeve et al., 2004’s paper presented a good description of the pathology behind RBD and how it links to DLB. It suggests that the loss of neurons in the locus coeruleus and substantia nigra, and subsequent dysregulation of cholinergic neurons in the pedunculopontine nucleus in DLB might disrupt normal REM sleep, as the pedunculopontine nucleus is thought to project cholinergic mesopontine neurons to the medullary reticular neurons, which inhibit the spinal motor neurons (Boeve et al., 2004). This in turn leads to atonia in REM sleep. Thus if there is a disruption to the normal workings of the pedunculopontine nucleus, atonia during REM sleep will be lost, leading to excessive motor activity. This has been further supported by case studies, such as a DLB patient’s autopsy report as described by Turner (2002), in which an examination of the substantia nigra and locus coeruleus revealed a significant amount of depigmentation, neuronal loss and up to five lewy bodies per neuron. Studies such as these have provided excellent evidence that these two disorders are interlinked. This link suggests that RSBD could be predictive of DLB and other parkinsonism disorders.

But why is the connection between these two disorders important? It has been found that there is are huge issues with clinical accuracy for DLB diagnosis, with consensus being between 22-83% and specificity between 87%-100% (Turner, 2002). Under-diagnosis and misdiagnosis appeared to be large problems within this, with DLB often mistaken for Alzheimer’s Disease. This is understandable, as DLB often occurs with a memory impairment, while hallucinations may not be reported and cognitive fluctuations remain difficult to define. It is essential that this changes, as correct diagnosis is necessary to ensure the best treatments and support are being given to such vulnerable patients. While RSBD and DLB may share similar pathological hallmarks, there is an additional reason that RSBD may provide a fundamental diagnostic marker for DLB. It has been reported to occur many years prior to the onset of cognitive impairments in DLB, with Turner (2002) reporting a case study of a 73 patient who suffered from RSBD up to 13 years before his first cognitive symptom was noticed.

It has been noted that RSBD can be clinically diagnosed, with screen tools (such as questionnaires) that hold efficient validity (Munhoz & Teive, 2014). Additionally, RSBD can be diagnosed using a polysomnography – with specific features being rapid eye movement and an elevated EMG tone. Video evidence is also usually recorded for diagnostic purposes. This has been viewed as the “gold standard” for RSBD assessment (Munhoz & Teive, 2014). With its widely accepted diagnosis, there is a possibility that RSBD could act as an early diagnostic marker for DLB, and thus could enhance the sensitivity and accuracy of diagnosis.

References

Boeve, B. F. (2010). REM sleep behavior disorder. Annals of the New York Academy of Sciences, 1184(1), 15-54.
Boeve, B. F., Silber, M. H., & Ferman, T. J. (2004). REM sleep behavior disorder in Parkinson’s disease and dementia with Lewy bodies. Journal of geriatric psychiatry and neurology, 17(3), 146-157.
Munhoz, R. P., & Teive, H. A. (2014). REM sleep behaviour disorder: How useful is it for the differential diagnosis of parkinsonism?. Clinical neurology and neurosurgery, 127, 71-74.
Turner, R. S. (2002). Idiopathic rapid eye movement sleep behavior disorder is a harbinger of dementia with Lewy bodies. Journal of geriatric psychiatry and neurology, 15(4), 195-199.

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