Neuroimaging Applications in Restless Legs Syndrome

Sensory aspects of restless legs syndrome: Clinical, neurophysiological and neuroimaging prospectives

Restless Legs Syndrome (RLS) is a complex sensorimotor disorder, classified among the sleep-related movement disorders. Although sensory symptoms appear as key features of the disorder, they are still poorly characterized from a clinical perspective and conceptualized from a pathophysiological point of view. In this review, we aim to describe the clinical and functional substrates of RLS, focusing mainly on its sensory symptoms and on their neurophysiological and anatomical correlates. Knowledge of both subjective sensory symptoms and objective sensory signs are still controversial. Current data also indicate that the sensory component of RLS seems to be subserved by anomalies of sensorimotor integration and by mechanism of central sensitization. Overall, electrophysiological findings highlight the involvement of multiple generators in the pathogenesis of RLS, eventually resulting in an increased nervous system excitability and/or alterations in inhibition within the somatosensory and nociceptive pathways. Structural and functional neuroimaging data show the involvement of several crucial areas and circuits, among which the thalamus appears to play a pivotal role. A holistic approach looking at brain connectivity, structural or functional abnormalities, and their interplay with molecular vulnerability and neurotransmitter alterations is warranted to disentangle the complex framework of RLS.

Large muscle group movements during sleep in restless leg syndrome: neurophysiological and clinical implications

STUDY OBJECTIVES

Recently, criteria have been drawn up for large muscle group movements during sleep (LMM), defined as movements lasting for 3-45 seconds in adults, which are often accompanied by changes in sleep stage, arousals, and increases in heart rate. The aim of this study was to characterize LMM in restless legs syndrome (RLS) in order to better evaluate their impact on the neurophysiology of the disorder and, therefore, the possible clinical implications.

METHODS

Consecutive, drug-free patients diagnosed with RLS and controls, aged 18 years or more, were retrospectively enrolled. Leg movement activity-short-interval (SILMS), periodic (PLMS), and isolated (ISOLMS) leg movements during sleep-and LMM were detected and scored.

RESULTS

In total, 100 patients and 67 controls were recruited. All movement measures were significantly higher in RLS. A significant positive correlation was found between LMM and ISOLMS index but not PLMS index in both groups. LMM index showed a significant negative correlation with total sleep time, sleep efficiency, and percentage of sleep stages N3 and R, as well as a significant positive correlation with the number of awakenings, and percentage of sleep stages N1 and N2 only in patients with RLS. No significant correlation was found between either LMM or PLMS index and RLS severity.

CONCLUSIONS

Different types of movements, including SILMS, ISOLMS, and LMM, play somewhat distinct roles in sleep neurophysiology in RLS. Notably, LMM, a newly recognized category of movements, demonstrates associations with sleep architecture instability and fragmentation, arousals, and awakenings, suggesting potential clinical implications.

Recognition of emotional face expressions in patients with restless legs syndrome

OBJECTIVE

Restless legs syndrome (RLS) is one of the commonest neurologic diseases. Along with sensory and motor symptoms, cognitive impairment and psychiatric features can be seen with RLS. The present study, was planned to look for evidence of cognitive impairment by evaluating facial emotion recognition (FER) in patients with RLS.

METHODS

In this study, 80 patients with RLS and 50 healthy controls (HCs) were included. Demographic data were recorded. All patients with RLS and HCs were tested with Beck anxiety inventory (BAI), Beck depression inventory (BDI) and with Ekman's test for recognition of facial emotions.

RESULTS

Sixty-three of the patients with RLS and 37 of the HCs were female. The mean age of the patients was 45.41 ± 8.24, and the mean age of HCs was 43.12 ± 10.35. The patients and HCs were similar regarding sex, age, educational status, and marital status. Patients with RLS had FER difficulties comparing HCs. There was a negative correlation between Ekman's test scores and BDI (r = -0.311, p < 0.001) and BAI scores (r = -0.379, p < 0.001).

CONCLUSION

FER is an invaluable research topic regarding cognitive function in RLS, which may help us develop different perspectives in terms of revealing the pathophysiology and is very important for the well-being of the patients' social interactions.

Unveiling the pathophysiology of restless legs syndrome through transcriptome analysis

The aim of this study was to analyze signaling pathways associated with differentially expressed messenger RNAs in people with restless legs syndrome (RLS). Seventeen RLS patients and 18 controls were enrolled. Coding RNA expression profiling of 12,857 gene transcripts by next-generation sequencing was performed. Enrichment analysis by pathfindR tool was carried-out, with p-adjusted ≤0.001 and fold-change ≥2.5. Nine main different network groups were significantly dysregulated in RLS: infections, inflammation, immunology, neurodegeneration, cancer, neurotransmission and biological, blood and metabolic mechanisms. Genetic predisposition plays a key role in RLS and evidence indicates its inflammatory nature; the high involvement of mainly neurotropic viruses and the TORCH complex might trigger inflammatory/immune reactions in genetically predisposed subjects and activate a series of biological pathways-especially IL-17, receptor potential channels, nuclear factor kappa-light-chain-enhancer of activated B cells, NOD-like receptor, mitogen-activated protein kinase, p53, mitophagy, and ferroptosis-involved in neurotransmitter mechanisms, synaptic plasticity, axon guidance, neurodegeneration, carcinogenesis, and metabolism.

Review of the role of the endogenous opioid and melanocortin systems in the restless legs syndrome

Restless legs syndrome (RLS) is responsive to opioid, dopaminergic and iron-based treatments. Receptor blocker studies in RLS patients suggest that the therapeutic efficacy of opioids is specific to the opioid receptor and mediated indirectly through the dopaminergic system. An RLS autopsy study reveals decreases in endogenous opioids, β-endorphin and perhaps Met-enkephalin in the thalamus of RLS patients. A total opioid receptor knock-out (mu, delta and kappa) and a mu-opioid receptor knock-out mouse model of RLS show circadian motor changes akin to RLS and, although both models show sensory changes, the mu-opioid receptor knock mouse shows circadian sensory changes closest to those seen in idiopathic RLS. Both models show changes in striatal dopamine, anaemia and low serum iron. However, only in the total receptor knock-out mouse do we see the decreases in serum ferritin that are normally found in RLS. There are also decreases in serum iron when wild-type mice are administered a mu-opioid receptor blocker. In addition, the mu-opioid receptor knock-out mouse also shows increases in striatal zinc paralleling similar changes in RLS. Adrenocorticotropic hormone and α-melanocyte stimulating hormone are derived from pro-opiomelanocortin as is β-endorphin. However, they cause RLS-like symptoms and periodic limb movements when injected intraventricularly into rats. These results collectively suggest that an endogenous opioid deficiency is pathogenetic to RLS and that an altered melanocortin system may be causal to RLS as well.

White matter microstructure alterations in idiopathic restless legs syndrome: a study combining crossing fiber-based and tensor-based approaches

Introduction

Restless legs syndrome (RLS) is a common sensorimotor disorder characterized by an irrepressible urge to move the legs and frequently accompanied by unpleasant sensations in the legs. The pathophysiological mechanisms underlying RLS remain unclear, and RLS is hypothesized to be associated with alterations in white matter tracts.

Methods

Diffusion MRI is a unique noninvasive method widely used to study white matter tracts in the human brain. Thus, diffusion-weighted images were acquired from 18 idiopathic RLS patients and 31 age- and sex-matched healthy controls (HCs). Whole brain tract-based spatial statistics (TBSS) and atlas-based analyzes combining crossing fiber-based metrics and tensor-based metrics were performed to investigate the white matter patterns in individuals with RLS.

Results

TBSS analysis revealed significantly higher fractional anisotropy (FA) and partial volume fraction of primary (F1) fiber populations in multiple tracts associated with the sensorimotor network in patients with RLS than in HCs. In the atlas based analysis, the bilateral anterior thalamus radiation, bilateral corticospinal tract, bilateral inferior fronto-occipital fasciculus, left hippocampal cingulum, left inferior longitudinal fasciculus, and left uncinate fasciculus showed significantl increased F1, but only the left hippocampal cingulum showed significantly higher FA.

Discussion

The results demonstrated that F1 identified extensive alterations in white matter tracts compared with FA and confirmed the hypothesis that crossing fiber-based metrics are more sensitive than tensor-based metrics in detecting white matter abnormalities in RLS. The present findings provide evidence that the increased F1 metric observed in sensorimotor tracts may be a critical neural substrate of RLS, enhancing our understanding of the underlying pathological changes.

Reduced Interoception Abilities in Patients with Restless Legs Syndrome

Background

Restless legs syndrome (RLS) is a complex sensorimotor disorder occurring with a typical circadian fashion. Association with additional features, like alexithymia and nocturnal compulsive behaviors further complicates the framework.

Objectives

To assess interoception in RLS.

Methods

A total of 25 RLS patients and 28 controls underwent the heartbeat tracking task (interoceptive accuracy [IAC]). RLS symptoms' frequency, disturbance and duration, nocturnal behaviors, interoceptive awareness (IAW), alexithymia, depressive and anxiety symptoms were also collected.

Results

RLS patients showed significant lower IAC (P = 0.0003) and IAW (P = 0.012), and reported more nocturnal eating behaviors (P < 0.001). IAC positively correlated with IAW (R = 0.32), and negatively correlated with age (R = -0.58). Nocturnal eating behavior negatively correlated with IAC (R = -0.44) and IAW (R = -0.50).

Conclusions

RLS patients presented reduced interoceptive abilities correlating with higher nocturnal eating behaviors. Future studies are needed to explore the role of interoception in RLS pathophysiology, also in relation to other sensorimotor aspects.

Vitamin D and Restless Legs Syndrome: A Review of Current Literature

This review presents a detailed summary of the current literature regarding RLS and vitamin D deficiency. To our knowledge it is the first review of its kind. We review the prevalence of vitamin D deficiency in RLS as well as the evidence for the use of vitamin D supplementation in RLS management. We further examine the literature for proteomic and genetic evidence of a role for vitamin D in the pathogenesis of RLS. An alteration in vitamin D binding protein in RLS is one of the most consistent findings in the proteomic studies. Furthermore, we examine the interaction of vitamin D with calcium, phosphorus, and parathyroid hormone and the possible role of these connections in RLS. We also explore the possible nexus between RLS and vitamin D in renal disease, cardiovascular and cerebrovascular disease as well as inflammation. In addition, we review the potential interaction between vitamin D and RLS with iron, dopamine and other neurotransmitter systems including the endogenous opiate, serotoninergic, glutamatergic and adenosinergic systems. We also explore the role of vitamin D in RLS Augmentation (i.e., the paradoxical worsening of RLS symptoms when dopaminergic agents are used as a therapy for RLS). Although the literature is not entirely consistent in affirming vitamin D deficiency in RLS or the amelioration of RLS symptoms with vitamin D therapy, the collective studies overall indicate that vitamin D deficiency is common enough in RLS patients to suggest that RLS patients should have their vitamin D levels checked and any deficiency corrected as a standard of care.

Highlights 

Patients with Restless Legs Syndrome (RLS) may be deficient in vitamin D and therapy with vitamin D may ameliorate RLS. We present the first review dedicated solely to evaluating the relationship between RLS and vitamin D and present a case for the role of vitamin D in RLS pathogenesis.

Restless Legs Syndrome and the Eyes: Spectral-Domain Optic Coherence Tomography Study

BACKGROUND

Restless legs syndrome (RLS) is a movement disorder thought to be caused by impaired dopamine action. This study aimed to evaluate possible changes in ocular biometric and optic coherence tomography (OCT) parameters in RLS patients.

METHODS

This is a prospective, cross-sectional comparative study. Consecutive primary and secondary (with iron-deficiency anemia) RLS patients and age-matched and sex-matched controls were enrolled in the study. All participants underwent comprehensive neurological and ophthalmological examinations. Ocular biometric and OCT parameters, such as choroidal thickness, macular thickness, macular volume, ganglion cell layer thickness, inner nuclear cell layer thickness, and retinal nerve fiber layer thickness, were compared.

RESULTS

Fifty-one RLS patients and 50 healthy controls were included in this study. There was no difference between the groups' refraction status, ocular biometric data (axial length, anterior chamber depth, central corneal thickness), or OCT parameters (choroidal thickness, macular thickness, macular volume, ganglion cell layer thickness, inner nuclear cell layer thickness). Primary and secondary (with only iron-deficiency anemia) RLS patients were compared, and there was no difference in their axial length, anterior chamber depth, central corneal thickness or OCT parameters. No significant relationship was found between disease severity or duration and OCT parameters.

CONCLUSIONS

Disease severity and disease duration do not affect OCT parameters in primary or secondary RLS patients. OCT data do not seem to provide information about the course of this disease.

Restless sleep disorder, restless legs syndrome, and periodic limb movement disorder-Sleep in motion!

Sleep-related movement disorders (SRMDs) represent an important part of pediatric sleep disorders. The most common complaint in SRMD is restless sleep at night. Restless sleep is reported in up to 80% of children with restless legs syndrome (RLS) and children with periodic limb movements of sleep (PLMS) disorder (PLMD). However, restless sleep causing daytime behavioral consequences can be seen in children without another apparent condition and has recently been identified as a new independent primary pediatric sleep disorder, called restless sleep disorder (RSD). This study describes these three main SRMDs (RSD, RLS, and PLMD), explains the new consensus criteria for RSD, emphasizes the rapidly evolving areas of research in this field, and proposes recommendations for future research. In particular, the published data constitute convincing evidence that sleep-related movements are disruptors of sleep quality and continuity. However, while important advancements have recently been reported in adults, a detailed analysis of the phenomenology and consequences of sleep-related movements has just started in children. New approaches, standardized diagnostic methods, and specific guidelines are needed in the field of pediatric SRMD.

Evaluation of Brain SPECT with 99mTc-TRODAT-1 in the Differential Diagnosis of Parkinsonism

INTRODUCTION

Brain SPECT with ^99mTc-TRODAT-1 (SPECT-TRODAT) may be a useful tool in the differential diagnosis of Parkinsonism.

OBJECTIVE

To compare results of SPECT-TRODAT with clinical findings in patients with Parkinsonism.

METHODS

We evaluated 153 outpatients. SPECT-TRODAT results were visually analyzed into normal, abnormal, symmetric, and asymmetric, and according to the degree of impairment into mild, moderate, marked, and severe (1-4).

RESULTS

A direct relationship was found between motor scores severity (MDS-UPDRS-III) and SPECT-TRODAT-reduced binding in general, in the group of patients with synucleinopathies (rho = 0.258, p=0.005), especially in patients with Parkinson's disease (rho = 0.204, p=0.049). Changes in SPECT-TRODAT had high correspondence with symmetry in all Parkinsonism. When comparing groups to the correspondence predominantly bilateral or unilateral impairment in SPECT, there was a difference between patients with SNP (p=0.041) and between this group and patients with secondary Parkinsonism (SP) (p < 0.0001). It was handy in differentiating drug-induced Parkinsonism from synucleinopathies. In the group of drug-induced Parkinsonism, younger people were the ones who showed the most significant reductions in radiotracer uptake. In this group, nonmotor signs resulted in examinations with more significant reductions in radiotracer uptake. When the scans without alterations and those that did not correspond to the symmetry were considered negative, SPECT-TRODAT's accuracy and specificity to differentiate PD from other forms of Parkinsonism were low. There was an inverse correlation between the severity of the SPECT-TRODAT result and the absence of nonmotor signs in patients with drug-induced Parkinsonism.

CONCLUSION

The authors concluded that the SPECT with 99mTc-TRODAT-1 was mainly useful in differentiating between synucleinopathies and secondary Parkinsonism.

Morphological analysis of the brain subcortical gray structures in restless legs syndrome

BACKGROUND

Although several studies have shown the involvement of specific structures of the central nervous system, the dopaminergic system, and iron metabolism in restless legs syndrome (RLS), the exact location and extent of its anatomical substrate is not yet known. The scope of this new study was to investigate the brain subcortical gray structures, by means of structural magnetic resonance imaging (MRI) studies, in RLS patients in order to assess the presence of any volume or shape abnormalities involving these structures.

METHODS

Thirty-three normal controls (24 females and nine males) and 45 RLS patients (34 females and 11 males) were retrospectively recruited and underwent a 1.5 Tesla MRI study with two-dimensional T1 sequences in the sagittal plane. Post-processing was performed by means of the Functional Magnetic Resonance Imaging of the Brain Analysis Group Integrated Registration and Segmentation Tool (FIRST) software, and both volumetric and morphological analyses of the thalamus, caudate, putamen, globus pallidus, brainstem, hippocampus, and amygdala, bilaterally, were carried out.

RESULTS

A statistically significant volumetric reduction in the left amygdala and left globus pallidus was found in subjects with RLS, as well as large surface morphological alterations affecting the amygdala bilaterally and other less widespread surface changes in both hippocampi, the right caudate, the left globus pallidus, and the left putamen.

CONCLUSIONS

These findings seem to indicate that the basic mechanisms of RLS might include a pathway involving not only the hypothalamus-spinal dopaminergic circuit (nucleus A11), but also pathways including the basal ganglia and structures that are part of the limbic system; moreover, structural alterations in RLS seem to concern the morphology as well as the volume of the above structures. The role of basal ganglia in the complex neurophysiological and neurochemical mechanism of RLS needs to carefully reconsidered.

Phenotypical predictors of pregnancy-related restless legs syndrome and their association with basal ganglia and the limbic circuits

Restless legs syndrome (RLS) in pregnancy is a common disorder with a multifactorial etiology. A neurological and obstetrical cohort of 308 postpartum women was screened for RLS within 1 to 6 days of childbirth and 12 weeks postpartum. Of the 308 young mothers, 57 (prevalence rate 19%) were identified as having been affected by RLS symptoms in the recently completed pregnancy. Structural and functional MRI was obtained from 25 of these 57 participants. A multivariate two-window algorithm was employed to systematically chart the relationship between brain structures and phenotypical predictors of RLS. A decreased volume of the parietal, orbitofrontal and frontal areas shortly after delivery was found to be linked to persistent RLS symptoms up to 12 weeks postpartum, the symptoms' severity and intensity in the most recent pregnancy, and a history of RLS in previous pregnancies. The same negative relationship was observed between brain volume and not being married, not receiving any iron supplement and higher numbers of stressful life events. High cortisol levels, being married and receiving iron supplements, on the other hand, were found to be associated with increased volumes in the bilateral striatum. Investigating RLS symptoms in pregnancy within a brain-phenotype framework may help shed light on the heterogeneity of the condition.

Iron Deposition Characteristics of Deep Gray Matter in Elderly Individuals in the Community Revealed by Quantitative Susceptibility Mapping and Multiple Factor Analysis

Purpose

The objective of this study was to determine which factors influence brain iron concentrations in deep gray matter in elderly individuals and how these factors influence regional brain iron concentrations.

Methods

A total of 105 elderly individuals were enrolled in this study. All participants underwent detailed magnetic resonance imaging (MRI) examinations from October 2018 to August 2019. Among them, 44 individuals had undergone a previous MRI examination from July 2010 to August 2011. Quantitative susceptibility mapping (QSM) was utilized as an indirect quantitative marker of brain iron, and the susceptibility values of deep gray matter structures were obtained. Univariate analysis and multiple linear regression analysis were used to investigate 11 possible determinants for cerebral iron deposition.

Results

Our results showed no sex- or hemisphere-related differences in susceptibility values in any of the regions studied. Aging was significantly correlated with increased insusceptibility values in almost all analyzed brain regions (except for the thalamus) when we compared the susceptibility values at the two time points. In a cross-sectional analysis, the relationship between gray matter nucleus susceptibility values and age was conducted using Pearson’s linear regression. Aging was significantly correlated with the susceptibility values of the globus pallidus (GP), putamen (Put), and caudate nucleus (CN), with the Put having the strongest correlations. In multiple linear regression models, associations with increased susceptibility values were found in the CN, Put, red nucleus, and dentate nucleus for individuals with a history of type 2 diabetes mellitus (T2DM). However, the patients with hypertension showed significantly reduced susceptibility values in the red nucleus and dentate nucleus. Our data suggested that smokers had increased susceptibility values in the thalamus. No significant associations were found for individuals with a history of hypercholesterolemia and Apolipoprotein E4 carrier status.

Conclusion

Our data revealed that aging, T2DM, and smoking could increase iron deposition in some deep gray matter structures. However, hypertension had the opposite effects in the red nuclei and dentate nuclei. Brain iron metabolism could be influenced by many factors in different modes. In future studies, we should strictly control for confounding factors.

Grey matter alterations in restless legs syndrome: A coordinate-based meta-analysis

Brain structural abnormalities in idiopathic restless legs syndrome have long been debated. Voxel-based morphometry is an objective structural magnetic resonance imaging technique to investigate regional grey matter volume or density differences between groups. In the last decade, voxel-based morphometry studies have exhibited inconsistent and conflicting findings regarding the presence and localization of brain grey matter alterations in restless legs syndrome. We therefore conducted a coordinate-based meta-analysis to quantitatively examine whether there were consistent grey matter findings in restless legs syndrome using the latest algorithms, seed-based d mapping with permutation of subject images. We included 12 voxel-based morphometry studies (13 datasets, 375 patients and 385 healthy controls). Our coordinate-based meta-analysis did not identify evidence of consistent grey matter alterations in restless legs syndrome. Grey matter alterations via voxel-based morphometry analysis are not therefore recommended to be used as a reliable surrogate neuroimaging marker for restless legs syndrome. This lack of consistency may be attributed to differences in sample size, genetics, gender distribution and age at onset, clinical heterogeneity (clinical course, anatomical distribution of symptoms, disease severity, disease duration, abnormal sensory profiles and comorbidity), and variations in imaging acquisition, data processing and statistical strategies. Longitudinal studies with multimodal neuroimaging techniques are needed to determine whether structural changes are dynamic and secondary to functional abnormalities.

Differential functional connectivity in thalamic and dopaminergic pathways in restless legs syndrome: a meta-analysis

Objective:

Restless legs syndrome (RLS) is a sensorimotor disorder with alterations in somatosensory processing in association with a dysfunctional cerebral network, involving the basal ganglia, limbic network, and sensorimotor pathways. Resting state functional magnetic resonance imaging (MRI) is a powerful tool to provide in vivo insight into functional processing and as such is of special interest in RLS considering the widespread pattern of networks involved in this disorder. In this meta-analysis of resting state functional MRI studies, we analyzed the preponderance of functional connectivity changes associated with RLS and discussed possible links to sensorimotor dysfunction and somatosensory processing.

Methods:

A systematic research using the online library PubMed was conducted and a total of seven studies passed the inclusion criteria of the meta-analysis. The results of these studies were merged and a statistical probability map was generated that indicated the likelihood of functional connectivity changes within the combined cohort, both for increased and decreased connectivity.

Results:

The meta-analysis demonstrated decreased functional connectivity within the dopaminergic network in participants with RLS compared with healthy controls, including the nigrostriatal, mesolimbic, and mesocortical pathways. Increased functional connectivity was observed bilaterally in the thalamus, including its ventral lateral, ventral anterior, and ventral posterior lateral nuclei, and the pulvinar.

Discussion:

Sensorimotor dysfunction in RLS seems to be reflected by decreased functional connectivity within the dopaminergic pathways. Network extension in the thalamus can be regarded as an adaptation to somatosensory dysfunction in RLS. This differential functional connectivity pattern extends prior findings on cerebral somatosensory processing in RLS and offers an explanation for the efficacy of dopaminergic treatment.