The preservation of muscle tone during REM phases is the single most important symptom of RBD. It entails involuntary myoclonic jerks throughout the body as well as movements of limbs and head, likely resembling motor dream enactment [6]. Affected individuals execute possibly aggressive or violent motions that may lead to self-injury, harm to third parties and damage to objects [7]. More complex presentations have also been described. Patients may gesture, punch, kick, sit up or leap from bed, grab somebody or something [8]. Their behavior is generally unintentional and not directed against a determined person or item. They may or may not wake up and recall their vivid dreams. Fatigue and excessive daytime sleepiness are a common consequence of RBD [9].

Ventilation is usually not affected.

• Nocturnal Awakening

  questions on nocturnal vocalization (6.1), sudden-limb movements (6.2), complex movements (6.3) or bedding items that fall down (6.4); items 7 and 8, nocturnal awakenings; item 9, general disturbances of sleep; and item 10, the presence of any neurological [bmcneurol.biomedcentral.com]

• Compulsive Disorder

  In addition, a 31-year-old man with obsessive-compulsive disorder developed RBD soon after starting fluoxetine therapy, which persisted at PSG study 19 months after fluoxetine discontinuation. [ncbi.nlm.nih.gov]

• Somnambulism

  Somnambulism Sitting, walking, or other complex behaviors occur during sleep, usually with the eyes open but without evidence of recognition. [merckmanuals.com]

  Differential diagnosis Several sleep disorders causing behaviors in sleep can be considered in the differential diagnosis, such as sleep walking (somnambulism), sleep terrors, nocturnal seizures, nightmares, psychogenic dissociative states, post-traumatic [bjmp.org]

  NREM parasomnias including night terrors, somnambulism, and confusional arousals are most prevalent in pediatric populations. [ncbi.nlm.nih.gov]

  Anna Szűcs, Anita Kamondi, Rezső Zoller, Gábor Barcs, Pál Szabó and György Purebl, Violent somnambulism: A parasomnia of young men with stereotyped dream-like experiences, Medical Hypotheses, 83, 1, (47), (2014). [doi.org]

• Fine Tremor

  A 72-year-old woman was admitted complaining of fine tremor of the right hand and weakness of the right lower extremity. She was diagnosed as having CBD on the basis of clinical features and neuroimaging studies. [ncbi.nlm.nih.gov]

• Postural Instability

  REM sleep behavior disorder is not linked to postural instability and gait dysfunction in Parkinson. [ncbi.nlm.nih.gov]

• Stupor

  Oneiric stupor: the peculiar behaviour of agrypnia excitata. Sleep Med. 2011 Dec; 12 (Suppl. 2):S64–7. [ PubMed ] [ Google Scholar ] [121] Boeve BF, Maraganore DM, Parisi JE, Ahlskog JE, Graff-Radford N, Caselli RJ, et al. [ncbi.nlm.nih.gov]

• Loss of Gait

  INTRODUCTION: Rapid eye movement (REM) sleep behavior disorder (RBD) in Parkinson's disease (PD) is associated with differences in clinical phenotype, including dementia, autonomic loss, and gait dysfunction. [ncbi.nlm.nih.gov]

• Nocturia

  Sedating medications should be ceased and obstructive sleep apnea, primary sleep disorders, and nocturia should be ruled out. Caffeine is a useful treatment in those without periodic leg movement disorder of sleep or restless leg syndrome [ 95 ]. [doi.org]

Diagnostic criteria for RBD have been defined as follows by the American Academy of Sleep Medicine [10]:

• Involuntary movements are associated with dreams

As well as either one of the following:

• Harmful or potentially harmful behavior during sleep
• Motor dream enactment
• Disruption of sleep continuity

The diagnosis of RBD may be based on these minimal criteria, but is ideally supported by the following polysomnographic findings as obtained during REM sleep:

• Increased chin electromyography tone
• Enhanced chin or limb phasic electromyography twitching associated with excessive myoclonic jerks or complex, vigorous, or violent behavior or the absence of epileptiform activity

These criteria apply if mental disorders have been ruled out. In contrast, concomitant neurodegenerative disease or other neurological disorder are not to be considered at this point. In fact, a considerable subset of RBD patients suffers from additional pathologies like Parkinson's disease.

• EEG Slowing

  Some prospective results in iRBD showed that potential markers of neurodegeneration are the following: 1) marked EEG slowing on spectral analysis; 2) decreased striatal 123I-FPCIT; 3) impaired color vision. [ncbi.nlm.nih.gov]

• Neurofibrillary Tangle

  After death, semiquantitative analyses were conducted for synuclein, amyloid, neurofibrillary tangles, and cerebrovascular lesions. RESULTS: Forty cases had probable RBD (PD RBD), and 41 did not (PD-RBD). [ncbi.nlm.nih.gov]

Physiologically, longer periods of non-REM sleep are interrupted by short REM phases. A complete sleep cycle comprising all four stages of non-REM sleep as well as a REM phase usually lasts about 100 minutes [1]. Both disturbances of non-REM or REM sleep and irregular cycling are related to sleep disorders.

Dreaming typically occurs during REM sleep. Accordingly, REM phases are characterized by bursts of rapid eye movement, increase of the brain and sympathetic nerve activity, heart rate, and blood pressure, as well as irregular respiration and the absence of muscle tone [2]. Enhanced brain activity is reflected in wake-like electroencephalograms, loss of muscle tone may be depicted by means of electromyography [1]. The preservation of muscle tone during REM phases is pathologic, and affected individuals are diagnosed with REM sleep behavior disorder (RBD), a type of parasomnia [3].

Although the majority of cases is deemed idiopathic, incidence rates are markedly increased among patients suffering from neurodegenerative disorders like Parkinson's disease, dementia with Lewy bodies and multiple system atrophy. In this context, RBD has been proposed as a risk factor for neurodegenerative diseases, and have been shown to precede the latter by decades [4]. This may have major implications for the diagnosis and early treatment of the respective entities. RBD may also be seen in individuals taking antidepressants and in those abusing or withdrawing from alcohol or drugs [5].

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