White and gray matter abnormalities in idiopathic rapid eye movement sleep behavior disorder: a diffusion-tensor imaging and voxel-based morphometry study

Cognition in rapid eye movement sleep behavior disorder

Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia characterized by excessive muscle activity and undesirable motor events during REM sleep. RBD occurs in approximately 0.5% of the general population, with a higher prevalence in older men. RBD is a frequent feature of dementia with Lewy bodies (DLB), but is only rarely reported in Alzheimer’s disease. RBD is also a risk factor for α-synuclein-related diseases, such as DLB, Parkinson’s disease (PD), and multiple system atrophy. Therefore, RBD has major implications for the diagnosis and treatment of neurodegenerative disorders and for understanding specific neurodegeneration patterns. Several markers of neurodegeneration have been identified in RBD, including cognitive impairments such as deficits in attention, executive functions, learning capacities, and visuospatial abilities. Approximately 50% of RBD patients present mild cognitive impairment. Moreover, RBD is also associated with cognitive decline in PD.

Decision making and executive functions in REM sleep behavior disorder

STUDY OBJECTIVES

This study was designed to assess decision making and executive functions in patients with idiopathic REM sleep behavior disorder (iRBD). IRBD is often seen as an early sign of later evolving neurodegenerative disease, most importantly Parkinson disease (PD) and Lewy body dementia (DLB). It has been proposed that iRBD patients show a cognitive profile similar to patients with PD.

DESIGN

All participants performed an extensive test battery tapping executive functions as well as the IOWA gambling task, which measures decision making under ambiguity.

SETTING

University hospital sleep disorders center.

PARTICIPANTS

16 iRBD patients and 45 age- and education-matched controls.

INTERVENTION

N.A.

MEASUREMENTS AND RESULTS

Compared with controls, iRBD patients showed disadvantageous decision making under ambiguity and did not learn by feedback over the task. IRBD patients' decision pattern was characterized by the lack of a consistent strategy, as indicated by frequent shifts between the single choices. A high proportion of iRBD patients (75%) showed random performance or worse even at the end of the task. No group differences were found in tasks assessing information sampling, flexibility and categorization, problem solving, and impulsivity.

CONCLUSIONS

As suggested by the present investigation, iRBD patients may show difficulties in decision making under ambiguity in a stage when other cognitive functions are relatively well preserved. Whether this is driven by subgroups of patients prone to develop PD or DLB has to be assessed by follow-up investigations.

Does idiopathic REM sleep behavior disorder (iRBD) really exist? What are the potential markers of neurodegeneration in iRBD?

REM sleep behavior disorder (RBD) may be idiopathic or associated with other neurologic disorders. A strong association between RBD and α-synucleinopathies has recently been observed, with the parasomnia often heralding the clinical onset of the neurodegenerative disease. The idiopathic form accounts for up to 60% of the cases reported in the three largest series of patients with RBD. Some clinical follow-up studies revealed that a large proportion of these patients will eventually develop a parkinsonian syndrome or a dementia of the Lewy bodies type in the years following the RBD diagnosis. The estimated 10-year risk of neurodegenerative disease for idiopathic RBD is about 40%. Moreover, it has been reported that the median interval between RBD and subsequent neurologic syndrome is 25years. Several studies have looked at neurophysiologic and neuropsychological functions in idiopathic RBD and have found evidence of CNS dysfunction during both wakefulness and sleep in a variable proportion of these patients, challenging the concept of idiopathic RBD. Identifying subjects with a high risk of developing a neurodegenerative process may be crucial to develop early intervention strategies. Prospective studies in idiopathic RBD showed that potential markers of neurodegeneration include: (1) marked EEG slowing on spectral analysis; (2) decreased striatal 123I-FP-CIT binding and substantia nigra hyperechogenicity; (3) impaired olfactory function; (4) impaired color vision.

Increased Corticomuscular Coherence in Idiopathic REM Sleep Behavior Disorder

The authors hypothesized that if locomotor drive increases along with rapid eye movement (REM) sleep without atonia in idiopathic REM sleep behavior disorder (RBD), then RBD patients would have greater corticomuscular coherence (CMC) values during REM sleep than at other sleep stages and than in healthy control subjects during REM sleep. To explore this hypothesis, we analyzed beta frequency range CMC between sensorimotor cortex electroencephalography (EEG) and chin/limb muscle EMG in idiopathic RBD patients. Eleven drug naive idiopathic RBD patients and 11 age-matched healthy control subjects were included in the present study. All participants completed subjective sleep questionnaires and underwent polysomnography for one night. The CMC value between EEGs recorded at central electrodes and EMGs acquired at leg and chin muscles were computed and compared by repeated measures analysis of variance (ANOVA). Sleep stages and muscle (i.e., chin vs. leg) served as within-subject factors, and group served as the between-subject factor. Repeated measures ANOVA revealed no significant main effect of group (F_1,20 = 0.571, p = 0.458) or muscle (F_1,20 = 1.283, p = 0.271). However, sleep stage was found to have a significant main effect (F_2.067,41.332 = 20.912, p < 0.001). The interaction between group and sleep stage was significant (F_2.067,41.332 = 3.438, p = 0.040). RBD patients had a significantly higher CMC value than controls during REM sleep (0.047 ± 0.00 vs. 0.052 ± 0.00, respectively, p = 0.007). This study reveals increased CMC during REM sleep in patients with RBD, which indicates increased cortical locomotor drive. Furthermore, this study supports the hypothesis that sufficient locomotor drive plays a role in the pathophysiology of RBD in addition to REM sleep without atonia.

Sleep-related problems in neurologic diseases

There is a strong association between sleep-related problems and neurologic diseases. Neurologic diseases of the CNS can directly cause sleep problems when sleep-wake mechanisms associated with the ascending reticular activating system are involved. The major sleep disorders associated with neurologic problems are outlined in the International Classification of Sleep Disorders, 2nd edition, as hypersomnias of central origin, sleep-related breathing disorders, the insomnias, circadian rhythm sleep disorders, sleep-related movement disorders, parasomnias, and sleep-related epilepsy. In a patient with CNS disease and excessive sleepiness, sleep-related breathing disorders should be a first concern, given the known association between obstructive sleep apnea (OSA) and cerebrovascular disease and the potential confounding effects that OSA might have on an otherwise compromised ischemic CNS penumbra. A basic knowledge of the anatomy and physiology of the sleep-wake mechanisms provides a rationale for pharmacologic intervention. Nonpharmacologic treatments are also important, especially when sleep-related breathing disorders are a concern. In addition, as patients with neurologic diseases are often prone to the adverse effects of many medications, the specific treatment regimen for any given individual should always include good sleep hygiene practices that use cognitive behavioral therapy.

REM sleep behavior disorder: motor manifestations and pathophysiology

Patients with REM sleep behavior disorder (RBD) enact violent dreams during REM sleep in the absence of normal muscle atonia. This disorder is highly frequent in patients with synucleinopathies (60%-100% of patients) and rare in patients with other neurodegenerative disorders. The disorder is detected by interview plus video and sleep monitoring. Abnormal movements expose the patients and bed partners to a high risk of injury and sleep disruption. The disorder is usually alleviated with melatonin and clonazepam. Limb movements are mainly minor, jerky, fast, pseudohallucinatory, and repeated, with a limp wrist during apparently grasping movements, although body jerks and complex violent (fights) and nonviolent culturally acquired behaviors are also observed. Notably, parkinsonism disappears during RBD-associated complex behaviors in patients with Parkinson's disease and with multiple system atrophy, suggesting that the upper motor stream bypasses the basal ganglia during REM sleep. Longitudinal studies show that idiopathic RBD predisposes patients to later develop Parkinson's disease, dementia with Lewy bodies, and, more rarely, multiple system atrophy, with a rate of conversion of 46% within 5 years. During this time window, patients concomitantly develop nonmotor signs (decreased olfaction and color vision, orthostatic hypotension, altered visuospatial abilities, increased harm avoidance) and have abnormal test results (decreased putamen dopamine uptake, slower EEG). Patients with idiopathic RBD have higher and faster risk for conversion to Parkinson's disease and dementia with Lewy bodies if abnormalities in dopamine transporter imaging, transcranial sonography, olfaction, and color vision are found at baseline. They constitute a highly specific target for testing neuroprotective agents.

White and gray matter abnormalities in narcolepsy with cataplexy

STUDY OBJECTIVES

The authors applied diffusion-tensor imaging including measurements of mean diffusivity (MD), which is a parameter of brain tissue integrity, fractional anisotropy (FA), which is a parameter of neuronal fiber integrity, and voxel-based morphometry, which is a measure of gray and white matter volume, to detect brain tissue changes in patients with narcolepsy-cataplexy.

DESIGN

N/A.

PATIENTS

Patients with narcolepsy-cataplexy (n = 16) and age-matched healthy control subjects (n = 12) were studied.

INTERVENTIONS

Whole cerebral MD, FA measures, and the volumes of the gray and white matter compartments were analyzed using statistical parametric mapping.

MEASUREMENT AND RESULTS

Significant MD increases and concomitant FA decreases were localized in the fronto-orbital cortex (P < 0.001) and the anterior cingulate (FA, P < 0.001; MD, P = 0.03) in narcolepsy-cataplexy. Additional MD increases without FA changes were detected in the ventral tegmental area, the dorsal raphe nuclei (P < 0.001), and the hypothalamus (P < 0.01). FA signal decreases were observed in the white matter tracts of the inferior frontal and inferior temporal cortices of narcolepsy-cataplexy patients (P < 0.001). Brain volume loss was evident in focal areas of the inferior and superior temporal cortices (P < 0.001) and the cingulate (P = 0.038).

CONCLUSIONS

Areas of increased diffusivity in the hypothalamus appear consistent with hypocretinergic cell loss reported in narcolepsy-cataplexy. Signal abnormalities in the ventral tegmental area and the dorsal raphe nuclei correspond to major synaptic targets of hypocretin neurons that were associated with the regulation of the sleep-wake cycle. Brain tissue alterations identified in the frontal cortex and cingulate are crucial in the maintenance of attention and reward-dependent decision making, both known to be impaired in narcolepsy-cataplexy.

Magnetization transfer and adiabatic R 1ρ MRI in the brainstem of Parkinson's disease

BACKGROUND

In addition to classic midbrain pathology, Parkinson's disease (PD) is accompanied by changes in pontine and medullary brainstem structures. These additional abnormalities may underlie non-motor features as well as play a role in motor disability.

METHODS

Using novel magnetic resonance imaging (MRI) methods based on rotating frame adiabatic R(1ρ) (i.e., measurements of longitudinal relaxation during adiabatic full passage pulses) and modified magnetization transfer (MT) MRI mapping, we sought to identify brainstem alterations in nine individuals with mild-moderate PD (off medication) and ten age-matched controls at 4 T.

RESULTS

We discovered significant differences in MRI parameters between midbrain and medullary brainstem structures in control subjects as compared to PD patients.

CONCLUSIONS

These findings support the presence of underlying functional/structural brainstem changes in mild-moderate PD.

Neuroimaging in the early diagnosis of neurodegenerative disease

Functional imaging may be useful for both the early diagnosis as well as preclinical detection of neurodegenerative disease. Additionally, while structural imaging has traditionally been regarded as a tool to exclude alternate diagnoses, recent advances in magnetic resonance show promise for greater diagnostic specificity. The role of MR and radionuclide imaging in early diagnosis and preclinical detection of dementia and parkinsonism are reviewed here.

Brainstem and spinal cord circuitry regulating REM sleep and muscle atonia

Background

Previous work has suggested, but not demonstrated directly, a critical role for both glutamatergic and GABAergic neurons of the pontine tegmentum in the regulation of rapid eye movement (REM) sleep.

Methodology/Principal Findings

To determine the in vivo roles of these fast-acting neurotransmitters in putative REM pontine circuits, we injected an adeno-associated viral vector expressing Cre recombinase (AAV-Cre) into mice harboring lox-P modified alleles of either the vesicular glutamate transporter 2 (VGLUT2) or vesicular GABA-glycine transporter (VGAT) genes. Our results show that glutamatergic neurons of the sublaterodorsal nucleus (SLD) and glycinergic/GABAergic interneurons of the spinal ventral horn contribute to REM atonia, whereas a separate population of glutamatergic neurons in the caudal laterodorsal tegmental nucleus (cLDT) and SLD are important for REM sleep generation. Our results further suggest that presynaptic GABA release in the cLDT-SLD, ventrolateral periaqueductal gray matter (vlPAG) and lateral pontine tegmentum (LPT) are not critically involved in REM sleep control.

Conclusions/Significance

These findings reveal the critical and divergent in vivo role of pontine glutamate and spinal cord GABA/glycine in the regulation of REM sleep and atonia and suggest a possible etiological basis for REM sleep behavior disorder (RBD).

Voxel-based magnetic resonance imaging study of structural brain changes in patients with idiopathic REM sleep behavior disorder

PURPOSE

Rapid eye movement (REM) sleep behavior disorder (RBD) is considered to result from dysfunction of the brain stem structures that regulate REM sleep. In this study, we investigated structural brain changes using magnetic resonance imaging (MRI) in patients with idiopathic RBD (iRBD) to determine structural brain alterations associated with the disorder.

METHODS

Voxel-based MRI morphometry was applied to 20 patients with iRBD and findings were compared with those from 18 age-matched controls.

RESULTS

Compared with the controls, the patients with iRBD had significant gray matter volume reduction in the anterior lobes of the right and left cerebellum, tegmental portion of the pons, and left parahippocampal gyrus.

CONCLUSION

The present study provides in vivo evidence suggesting that structural lesions of the brain stem are responsible for the occurrence of iRBD. In addition, the pattern of gray matter loss is consistent with morphological changes commonly observed in patients with Lewy body disease and multiple system atrophy, indicating that iRBD can share a common morphological abnormality with alpha-synucleinopathies.

Sleep-wake changes in the premotor stage of Parkinson disease

Longitudinal studies in Parkinson disease (PD) have shown that the prevalence of sleep disorders increases with advanced disease. However, two sleep disorders, namely excessive daytime sleepiness (EDS) and REM sleep behavior disorder (RBD) have been described to antedate the development of the classical motor signs and symptoms of PD. One epidemiological study from the Honolulu-Asia Aging Study showed that aging men who reported "being sleepy most of the daily" had a threefold excess risk for developing PD after a seven-year follow-up. The origin and nature of EDS were not investigated. This study needs to be replicated. More robust data exist regarding RBD as the first manifestation of PD. RBD subjects commonly develop parkinsonism and cognitive impairment with time. Patients with the idiopathic form of RBD with decreased striatal dopamine transporters imaging, substantia nigra hyperechogenicity and hyposmia have an increased short-term risk for developing the classical motor, dysautonomic and cognitive symptoms of a synucleinopathy. Patients with idiopathic RBD, particularly those with abnormal subclinical features seen in the synucleinopathies such as decreased striatal dopamine transporters uptake, are the ideal population to be tested with disease-modifying agents in order to stop or slow down neurodegeneration in the brain.

Medical comorbidity of sleep disorders

PURPOSE OF REVIEW

Recently published literature indicates that sleep disorders present with medical comorbidities quite frequently. The coexistence of a sleep disorder with a medical disorder has a substantial impact for both the patient and the health system.

RECENT FINDINGS

Insomnia and hypersomnia are highly comorbid with medical conditions, such as chronic pain and diabetes, as well as with various cardiovascular, respiratory, gastrointestinal, urinary and neurological disorders. Restless legs syndrome and periodic leg movement syndrome have been associated with iron deficiency, kidney disease, diabetes, and neurological, autoimmune, cardiovascular and respiratory disorders. Rapid eye movement behaviour disorder has been described as an early manifestation of serious central nervous system diseases; thus, close neurological monitoring of patients referring with this complaint is indicated.

SUMMARY

Identification and management of any sleep disorder in medical patients is important for optimizing the course and prognosis. Of equal importance is the search for undetected medical disorder in patients presenting with sleep disorders.