Gray matter alteration in patients with restless legs syndrome: a voxel-based morphometry study

Redefining the role of the cerebellum in restless legs syndrome

OBJECTIVES

We aimed to investigate alterations in cerebellar volume and the intrinsic cerebellar network in patients with restless legs syndrome (RLS).

METHODS

We recruited 69 patients with RLS and 50 healthy controls who underwent brain magnetic resonance imaging (MRI), including three-dimensional T1-weighted imaging. The total cerebellar volume and cerebellar volume subdivisions were analyzed through automatic cerebellum anatomical parcellation using U-Net with locally constrained optimization program. The intrinsic cerebellar network was calculated through brain analysis using a graph theory program based on the cerebellar volume subdivisions. The cerebellar volumes and intrinsic cerebellar networks were compared between patients with RLS and healthy controls.

RESULTS

The cerebellar volume and subdivisions in patients with RLS did not show significant differences compared to those in healthy controls. However, significant alterations were observed in the intrinsic cerebellar network of patients with RLS. Increased mean clustering coefficient (0.185 vs. 0.114; p = 0.047) and small-worldness index (0.927 vs. 0.800; p = 0.047) were observed in patients with RLS. Additionally, total cerebellar volume was negatively correlated with the Pittsburgh Sleep Quality Index (r = -0.398; p = 0.020) and Insomnia Severity Index (ISI; r = -0.396; p = 0.011). Negative correlations were additionally observed between the right X lobule volume and the International Restless Legs Syndrome Severity Scale (r = -0.425; p = 0.008) and between the vermis VIII volume and ISI score (r = -0.399; p = 0.011).

CONCLUSION

We demonstrated alterations in the intrinsic cerebellar network in patients with RLS compared with healthy controls, showing increased connectivity with increased segregation in patients with RLS. This suggests a potential role of the cerebellum in RLS pathophysiology.

Cerebellum drives functional dysfunctions in restless leg syndrome

OBJECTIVE

Restless legs syndrome (RLS) has serious effects on patients' sleep quality, physical and mental health. However, the pathophysiological mechanisms of RLS remain unclear. This study utilized both static and dynamic functional activity and connectivity analyses approaches as well as effective connectivity analysis to reveal the neurophysiological basis of RLS.

METHODS

The resting-state functional MRI (rs-fMRI) data from 32 patients with RLS and 33 age-, and gender-matched healthy control (HC) were collected. Dynamic and static amplitude of low frequency fluctuation (ALFF), functional connectivity (FC), and Granger causality analysis (GCA) were employed to reveal the abnormal functional activities and couplings in patients with RLS.

RESULTS

RLS patients showed over-activities in left parahippocampus and right cerebellum, hyper-connectivities of right cerebellum with left basal ganglia, left postcentral gyrus and right precentral gyrus, and enhanced effective connectivity from right cerebellum to left postcentral gyrus compared to HC.

CONCLUSIONS

Abnormal cerebellum-basal ganglia-sensorimotor cortex circuit may be the underlying neuropathological basis of RLS. Our findings highlight the important role of right cerebellum in the onset of RLS and suggest right cerebellum may be a potential target for precision therapy.

Restless legs syndrome and cognitive function among adults: a systematic review and meta-analysis

BACKGROUND

Changes in the cognitive function of patients with restless legs syndrome is a growing area of research. Although several studies have been performed to investigate the association between restless legs syndrome (RLS) and cognitive function, the outcomes are still controversial. The meta-analysis aimed to elucidate the relationship between RLS and cognition, including global cognition and various cognitive domains including memory, attention, executive function, and spatial cognition.

METHODS

We searched the MEDLINE, EMBASE, and Web of Science databases from inception to November 2022 to screen eligible records. The means and standard deviations of cognitive test scores were obtained to calculate the standard mean difference and 95% confidence intervals.

RESULTS

A total of 1437 records were collected from the initial search and 16 records involving 4635 individuals were ultimately included in the systematic review and meta-analysis. Our data suggest negative associations between RLS and global cognition (SMD, - 0.42; 95% CI - 0.72 to - 0.11; I² = 76.6%) and attention (SMD, - 0.43; 95% CI - 0.73 to - 0.12; I² = 85.3%). No significant differences in memory (SMD, - 0.01; 95% CI - 0.31 to 0.28; I² = 68.0%), executive function (SMD, - 0.10; 95% CI, - 0.30 to 0.11; I² = 52.1%), or spatial cognition (SMD, - 0.17; 95% CI - 0.38 to 0.03; I² = 58.5%) were observed between the RLS and control groups. Moreover, the strength of the results was modified by age but not by sex or region.

CONCLUSIONS

Our findings suggest that RLS is negatively correlated with cognitive function, particularly global cognition and attention. However, the causal relationship, considering more confounders, is worthy of further exploration.

Periodic limb movements in sleep are linked to decreased hippocampus and amygdala volumes in the population-based BiDirect Study

STUDY OBJECTIVES

Even though numerous studies indicate that sleep disorders are associated with altered brain morphology, MRI studies focusing on periodic limb movements in sleep (PLMS) are scarce. Our aim was to investigate the association of PLMS with global and regional gray matter volumes as well as white matter hyperintensity (WMH) volume.

METHODS

One hundred and eighty-nine subjects (57.0 ± 7.8 years, women: 50.5%) of the population-based BiDirect Study underwent a single-night polysomnography (PSG). Standard criteria of the American Academy of Sleep Medicine were applied to evaluate sleep characteristics and calculate the PLMS index (PLMSI). T1w and FLAIR images were acquired with cerebral MRI at 3 Tesla. Voxel-based morphometry was performed to determine the total gray matter volume as well as the volume of cortical segments and subcortical gray matter areas using SPM12 and CAT12. The WMH volume was quantified with the Brain Intensity AbNormality Classification Algorithm. The independent relationship between MRI markers and PLMSI was analyzed using multivariable linear regression with adjustment for age, sex, body mass index, intracranial volume, PSG scorer, PSG device, sleep apnea, and the use of antidepressants.

RESULTS

PLMSI was not significantly related to global gray matter volume and WMH volume. However, significant inverse associations of the PLMSI with the volume of the hippocampus (left and right hemisphere) and left amygdala were observed.

CONCLUSIONS

A significant relationship between a higher PLMSI and lower volumes of the hippocampus and amygdala was found among the participants of the BiDirect Study. Since these associations are based on exploratory analyses, further replications are required before drawing firm conclusions.

Neuroanatomy and Functional Connectivity in Patients with Parkinson's Disease with or without Restless Legs Syndrome

INTRODUCTION

Restless legs syndrome (RLS) is a common non-motor symptom in Parkinson's disease (PD), but its pathogenesis remains unclear. This study aimed to explore the potential neural substrates of RLS in a large sample of patients with PD.

METHODS

A total of 42 patients with PD with RLS and 124 patients with PD without RLS were prospectively recruited at our hospital between February 2019 and October 2020 and underwent structural and resting-state functional magnetic resonance imaging. Differences between the two patient groups were assessed using voxel-based morphometry and functional connectivity analysis. PD duration, Part III of the Movement Disorder Society's Unified Parkinson's Disease Rating Scale (MDS-UPDRS-III) score, and levodopa equivalent daily dose were treated as covariates.

RESULTS

Patients with PD with RLS had significantly larger gray matter volume in the bilateral posterior cingulate cortex than patients with PD without RLS (FDR-adjusted P < 0.05). Compared to patients without RLS, those with RLS had significantly lower functional connectivity between the left central opercular cortex and the bilateral precentral gyri and postcentral gyri (FDR-adjusted P < 0.001).

CONCLUSION

Our study provides the first evidence that in patients with PD, RLS is associated with significantly larger gray matter volume in the posterior cingulate cortex and lower resting-state functional connectivity within the sensorimotor network. Our results may help clarify the pathophysiology of RLS in PD and identify possible therapeutic targets.

Sleep Dysfunction and Grey Matter Volume

PURPOSE OF REVIEW

With the voxel-based morphometry (VBM), structural imaging studies turned into new directions aiming to explore neurological disorders differently. This approach helps identify possible pathophysiological correlations between neuroanatomical grey matter (GM) structures in patients with sleep dysfunction. This article reviews recent findings on GM structure in various sleep disorders and possible causes of disturbed sleep and discusses the future perspectives.

RECENT FINDINGS

At present, research on the effect of GM volume changes in specific brain areas on the pathogenesis of sleep disturbances is incomplete. It remains unknown if the GM thickness reduction in patients with REM sleep behaviour disorder, obstructive sleep apnea, restless legs syndrome, and insomnia is due to complex disease presentation or direct response to disturbed sleep. Additionally, many VBM studies have yielded inconsistent results showing either reduction or increase in GM. The spatiotemporal complexity of whole-brain networks and state transitions during sleep and the role of GM changes increase new debates. Having multimodal data from large sample studies can help model sleep network dynamics in different disorders and provide novel data for possible therapeutic interventions.

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.

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.

Patterns of Gray Matter Volume Alterations in Hemodialysis Patients With and Without Restless Legs Syndrome: Evidence From a Voxel-Based Morphometry Study

PURPOSE

The purpose of this study was to investigate the differences of gray matter volume (GMV) alteration patterns between hemodialysis with restless legs syndrome (HD-RLS) and hemodialysis without restless legs syndrome (HD-nRLS) patients using voxel-based morphometry.

METHODS

Twenty-three HD-RLS patients, 27 HD-nRLS patients, and 27 age-, sex-, and education-matched healthy controls were included in this study. One-way analysis of covariance and post hoc analyses were used to assess differences in GMV, demographics, and clinical data among the 3 groups. Pearson correlation analysis was conducted between altered GMV in the HD-RLS group and clinical data.

RESULTS

Compared with HD-nRLS patients, HD-RLS patients showed decreased GMV in the left primary motor cortex (false discovery rate corrected, P < 0.05). Compared with the healthy controls, both HD subgroups (ie, those with and without RLS) exhibited consistent GMV changes, including decreased GMV in the bilateral anterior cingulate and paracingulate gyrus and left middle temporal gyrus (false discovery rate corrected, P < 0.05). The GMV values in the left precentral gyrus were negatively correlated with the RLS rating scores (r = 0.2138, P = 0.0263).

CONCLUSIONS

This abnormal decreased GMV in the sensorimotor cortex provides evidence for a sensory processing disorder in RLS that may be involved in the pathogenesis of RLS in HD patients.

Sensorimotor white matter projections and disease severity in primary Restless Legs Syndrome/Willis-Ekbom disease: a multimodal DTI analysis

BACKGROUND

Restless Legs Syndrome, a potentially disabling sleep disorder, also known as Willis-Ekbom disease (RLS/WED), may be caused by loss of inhibitory modulation of descending central motor pathways, structural changes in the somatosensory cortex, abnormal connectivity between motor and sensory areas, as well as by subtle abnormalities in white matter micro-organization.

OBJECTIVE

To compare diffusion-tensor imaging (DTI) metrics in areas associated with sensory or motor function, as well as sensorimotor integration, between subjects with primary mild-to-severe RLS/WED and controls.

METHODS

DTI metrics were assessed in 38 subjects with RLS/WED (14 mild to moderate, 24 severe to very severe) and 24 healthy age-matched controls with whole-brain Tract Based Spatial Statistics (TBSS), Region-of-interest (ROI) and probabilistic tractography based analyses. The ROIs corresponded to the corticospinal tract (CST) at the level of the cerebral peduncle; the superior, middle and inferior cerebellar peduncles. Subgroup analyses were made according to the severity of RLS/WED symptoms. The corticospinal tract was evaluated with probabilistic tractography. We also explored associations between significant findings and severity of symptoms with the Spearman's correlation coefficient.

RESULTS

TBSS analysis revealed decreased axial diffusivity (AD) in the left posterior thalamic radiation in RLS/WED. In subjects with severe RLS/WED, AD was reduced in the left posterior corona radiata and this reduction was negatively correlated with severity of symptoms. ROI-based analysis showed that radial diffusivity (RD) was increased in the superior cerebellar peduncles of individuals with severe RLS/WED. Tractography did not show between-group or subgroup differences.

CONCLUSIONS

Our results are consistent with subtle white matter changes, prominently in RLS/WED subjects with more severe symptoms, in areas related to sensory or motor function, as well as to sensorimotor integration, compared to controls. These findings support the hypothesis, raised by prior pathophysiological studies, of defective integration within these networks.

Statistical shape analysis of corpus callosum in restless leg syndrome

OBJECTIVES

In this study we aimed to investigate corpus callosum shape differences between restless leg syndrome patients and healthy controls, and to determine whether disease severity and duration are indicators for corpus callosum deformation in RLS patients.

METHODS

This study was conducted using the magnetic resonance imaging scans of 33 restless leg syndrome patients and 33 control subjects. Landmarks were marked on the digital images and callosal landmark coordinate data were used to assess shape difference by performing Generalized Procrustes analysis. The shape deformation from controls to the patients was evaluated performing the Thin Plate Spline approach.

RESULTS

There was a statistically significant shape difference between the groups. Highest deformation was determined at the posterior midbody of the corpus callosum. Growth curve analyses showed that with the increase in disease duration and severity, the CC size decreased.

DISCUSSION

The present study demonstrated callosal shape differences in restless leg syndrome using a landmark-based geometric morphometric approach, considering the topographic distribution of corpus callosum for the first time.

The Role of BTBD9 in the Cerebellum, Sleep-like Behaviors and the Restless Legs Syndrome

Recent genome-wide association studies (GWAS) have found cerebellum as a top hit for sleep regulation. Restless legs syndrome (RLS) is a sleep-related sensorimotor disorder characterized by uncomfortable sensations in the extremities, generally at night, which are often relieved by movements. Clinical studies have found that RLS patients have structural and functional abnormalities in the cerebellum. However, whether and how cerebellar pathology contributes to sleep regulation and RLS is not known. GWAS identified polymorphisms in BTBD9 conferring a higher risk of sleep disruption and RLS. Knockout of the BTBD9 homolog in mice (Btbd9) and fly results in motor restlessness and sleep disruption. We performed manganese-enhanced magnetic resonance imaging on the Btbd9 knockout mice and found decreased neural activities in the cerebellum, especially in lobules VIII, X, and the deep cerebellar nuclei. Electrophysiological recording of Purkinje cells (PCs) from Btbd9 knockout mice revealed an increased number of non-tonic PCs. Tonic PCs showed increased spontaneous activity and intrinsic excitability. To further investigate the cerebellar contribution to RLS and sleep-like behaviors, we generated PC-specific Btbd9 knockout mice (Btbd9 pKO) and performed behavioral studies. Btbd9 pKO mice showed significant motor restlessness during the rest phase but not in the active phase. Btbd9 pKO mice also had an increased probability of waking at rest. Unlike the Btbd9 knockout mice, there was no increased thermal sensation in the Btbd9 pKO. Our results indicate that the Btbd9 knockout influences the PC activity; dysfunction in the cerebellum may contribute to the motor restlessness found in the Btbd9 knockout mice.

Increased Gray Matter Density and Functional Connectivity of the Pons in Restless Legs Syndrome

BACKGROUND

Neurophysiological and radiological studies provide accumulating evidence for the involvement of the brainstem in the pathogenesis of restless legs syndrome (RLS). The analysis of the various subregions of the brainstem may help us better understand the pathophysiological mechanisms underlying the disorder. In this study, we investigated the structural and functional changes in the various subregions of the brainstem in RLS patients.

METHODS

The subregional changes in gray matter density and functional connectivity in the brainstem were analyzed in 20 drug-naive idiopathic RLS patients, as well as 18 normal control (NC) subjects for comparison. Correlation analyses and multivariate pattern analyses using linear support vector machine (SVM) were conducted.

RESULTS

We found significantly increased gray matter density in two clusters in the pons (designated pons_1 and pons_2) and in one cluster in the midbrain in RLS patients compared with NC subjects. Further functional connectivity analyses revealed significantly decreased functional connectivity between the midbrain and the right middle occipital gyrus, between pons_1 and the right orbital part of the superior frontal gyrus, and between pons_2 and the right parahippocampus in RLS compared with NC. Moreover, the functional connectivity between pons_2 and the right supplementary motor area (SMA) was significantly increased in RLS compared with NC. This change in RLS was marginally correlated with RS_RLS scores in the RLS patients. SVM-based classification showed an AUC of 0.955 using gray matter density of pons_2, and functional connectivity between pons_2 and SMA as features.

CONCLUSION

Collectively, our findings suggest that changes in gray matter density and functional connectivity in the pons may play a pathologic role in RLS. Furthermore, these abnormal changes in the pons might help to discriminate RLS from healthy subjects.

Resting-state connectivity and the effects of treatment in restless legs syndrome

OBJECTIVES

Resting-state brain connectivity has been shown to differ for Restless Legs Syndrome (RLS) compared to healthy control (CON) groups. This study evaluates the degree these RLS-CON differences are changed by concurrent treatment.

METHODS

Resting-state functional MRIs were obtained from 32 idiopathic RLS patients during the morning asymptomatic period and 16 age and gender-matched CON subjects. Of the 32 RLS patients, 16 were drug-naïve (DN-RLS), and 16 were regularly drug-treated using a dopamine agonist (DT-RLS). Various assessments of disease characteristics were also performed. The primary purpose was to assess the replicability of prior results and the effects of treatment on these differences between controls and untreated RLS patients. Resting-state connectivity was analyzed by a seed-based method using the bilateral ventral-posterolateral nuclei (VPLN) in the thalamus.

RESULTS

In the DN-RLS group, compared to the CON group, three areas (the bilateral lingual gyri and right middle temporal gyrus) were replicated. The three replicated areas did not significantly differ for DT-RLS compared to DN-RLS. DT-RLS compared to DN-RLS had significantly higher thalamic connectivity for the left uvula, right tuber, left anterior insula, and right declive.

CONCLUSIONS

Thalamic connectivity to the bilateral lingual gyri and right middle temporal gyrus is a replicable finding in DN-RLS that was not affected by dopamine agonist treatments. Other changes in thalamic connectivity were altered by dopamine agonist treatment. These treatment effects may be pertinent to the known treatment benefits of a dopamine agonist on RLS symptoms.

The role of BTBD9 in the cerebral cortex and the pathogenesis of restless legs syndrome

Restless legs syndrome (RLS) is a nocturnal neurological disorder affecting up to 10% of the population. It is characterized by an urge to move and uncomfortable sensations in the legs which can be relieved by movements. Mutations in BTBD9 may confer a higher risk of RLS. We developed Btbd9 knockout mice as an animal model. Functional alterations in the cerebral cortex, especially the sensorimotor cortex, have been found in RLS patients in several imaging studies. However, the role of cerebral cortex in the pathogenesis of RLS remains unclear. To explore this, we used in vivo manganese-enhanced MRI and found that the Btbd9 knockout mice had significantly increased neural activities in the primary somatosensory cortex (S1) and the rostral piriform cortex. Morphometry study revealed a decreased thickness in a part of S1 representing the hindlimb (S1HL) and M1. The electrophysiological recording showed Btbd9 knockout mice had enhanced short-term plasticity at the corticostriatal terminals to D1 medium spiny neurons (MSNs). Furthermore, we specifically knocked out Btbd9 in the cerebral cortex of mice (Btbd9 cKO). The Btbd9 cKO mice showed a rest-phase specific motor restlessness, decreased thermal sensation, and a thinner S1HL and M1. Both Btbd9 knockout and Btbd9 cKO exhibited motor deficits. Our results indicate that systematic BTBD9 deficiency leads to both functional and morphometrical changes of the cerebral cortex, and an alteration in the corticostriatal pathway to D1 MSNs. Loss of BTBD9 only in the cerebral cortex is sufficient to cause similar phenotypes as observed in the Btbd9 complete knockout mice.

Short-interval intracortical inhibition is decreased in restless legs syndrome across a range of severity

BACKGROUND

Decreased short-interval intracortical inhibition (SICI) to transcranial magnetic stimulation (TMS) of the primary motor cortex was described in subjects with restless legs syndrome/Willis-Ekbom disease (RLS/WED). It remained to be determined whether the magnitude of SICI decrease would be similar across levels of RLS/WED severity. Moreover, it was unknown whether, in addition to decreases in SICI, changes in cortical thickness or area could be detected in subjects with RLS/WED compared to controls. The objective of this study was to compare SICI, cortical thickness, and cortical area in subjects with idiopathic mild to moderate RLS/WED, severe to very severe RLS/WED, and controls.

METHODS

The severity of RLS/WED was assessed by the International Restless Legs Syndrome Severity Scale (IRLSS). SICI and 3T magnetic resonance imaging (MRI) data of subjects with RLS/WED and controls were compared. A receiver operating characteristic curve for SICI was designed for discrimination of participants with RLS/WED from controls. Cortical thickness and area were assessed by automated surface-based analysis.

RESULTS

SICI was significantly reduced in patients with mild to moderate and severe to very severe RLS/WED, compared to controls (one-way analysis of variance: F = 9.62, p < 0.001). Receiver operating characteristic curve analysis predicted RLS/WED when SICI was above 35% (area under the curve = 0.79, 95% CI 0.67-0.91, p < 0.001). Analyses of the whole brain and of regions of interest did not reveal differences in gray matter thickness or area between controls and subjects with RLS/WED.

CONCLUSION

SICI is an accurate cortical biomarker that can support the diagnosis of RLS/WED even in subjects with mild symptoms, but cortical thickness and area were not useful for discriminating subjects with this condition from controls.

Alterations of Sub-cortical Gray Matter Volume and Their Associations With Disease Duration in Patients With Restless Legs Syndrome

Object: The purpose of this study was to uncover the pathology of restless legs syndrome (RLS) by exploring brain structural alterations and their corresponding functional abnormality.

Method: Surface-based morphometry (SBM) and voxel-based morphometry (VBM) were performed to explore the alterations in cortical and sub-cortical gray matter volume (GMV) in a cohort of 20 RLS and 18 normal controls (NC). Furthermore, resting-state functional connectivity (RSFC) was also performed to identify the functional alterations in patients with RLS.

Results: We found significant alterations of sub-cortical GMV, especially the bilateral putamen (PUT), rather than alterations of cortical GMV in patients with RLS compared to NC using both SBM and VBM. Further sub-regional analysis revealed that GMV alterations of PUT was mostly located in the left dorsal caudal PUT in patients with RLS. In addition, altered RSFC patterns of PUT were identified in patients with RLS compared to NC. Moreover, correlation analyses showed that the GMV of the left caudate and the left ventral rostral PUT were positively correlated with disease duration in patients with RLS.

Conclusions: The alterations of subcortical GMV might imply that the primarily affected areas are located in sub-cortical areas especially in the sub-region of PUT by the pathologic process of RLS, which might be used as potential biomarkers for the early diagnosis of RLS.

Patterns of gray matter alterations in migraine and restless legs syndrome

Objectives

Migraine and restless legs syndrome (RLS) are often comorbid and share elements of pathology; however, their neuroanatomical underpinnings are poorly understood. This study aimed to identify patterns of gray matter volume (GMV) alteration specific to and common among patients with RLS, migraine, and comorbid migraine and RLS.

Methods

High‐resolution T1‐weighted images were acquired from 116 subjects: 27 RLS patients, 22 migraine patients, 22 patients with comorbid migraine and RLS, and 45 healthy controls. Direct group comparisons and conjunction analysis were first used to localize the distinct and shared neural signatures of migraine and RLS. We also investigated whether the shared neural signature could be replicated in an additional comorbid migraine/RLS group.

Results

Compared with healthy controls, migraine patients showed GMV changes in the lateral occipital cortex, cerebellum, frontal pole, and middle frontal gyrus (MFG), and RLS patients showed GMV changes in the thalamus, middle temporal gyrus, anterior cingulate cortex, insular cortex, and MFG. In migraine, compared with RLS, GMV differences were found in the precuneus, lateral occipital and occipital fusiform cortex, superior frontal and precentral gyri, and cerebellum. Conjunction analyses for these disorders showed altered GMV in the MFG, also found in patients with comorbid migraine and RLS. The GMV of the MFG also correlated with sleep quality in patients with comorbid migraine and RLS.

Interpretation

Migraine and RLS are characterized by shared and distinctive neuroanatomical characteristics, with a specific role of the MFG. These findings may be related to shared pathophysiology of these two distinct disorders.

Impaired Sensorimotor Integration in Restless Legs Syndrome

Objective: Restless legs syndrome (RLS) is a complicated sensorimotor syndrome that may be linked to changes in sensorimotor integration. The mechanism of such changes is unclear. The aim of this study was to investigate sensorimotor integration in patients with RLS through transcranial magnetic stimulation-motor evoked potentials (TMS-MEPs) preceded by peripheral electric stimulation.

Methods: Fourteen RLS patients and 12 healthy, age-matched controls were investigated. The clinical severity of RLS was evaluated based on the International Criteria of the International Restless Legs Syndrome Study Group (IRLSSG) severity scores. The tibial and median H-reflexes and the resting motor threshold (RMT) of the abductor pollicis brevis (APB) were tested in all 26 subjects. The RMT of the tibialis anterior (TA) was tested in 8 patients and 7 controls. All 26 subjects underwent measurement of unconditioned MEPs of the APB. Electric pulses were applied to the right median nerve, followed by TMS pulses over the left motor cortex at interstimulus intervals (ISIs) of 20, 25, 30, 50, 100, 150, and 200 ms. Unconditioned MEPs of the TA were measured in 8 patients and 7 controls. Electric pulses were applied to the right peroneal nerve, followed by TMS pulses over the left motor cortex at ISIs of 30, 35, 45, 60, 100, and 200 ms. The degree of modulation of MEPs by electric stimulation was expressed as the ratio of the conditioned MEP amplitude to the unconditioned MEP amplitude. Ratios <1 indicated inhibition, and ratios >1 indicated facilitation.

Results: No significant differences in RMT or H-reflex latencies or amplitudes were found between RLS patients and controls. A significant increase in unconditioned MEP amplitudes of the TA was observed in patients compared to controls (p = 0.03). Long-latency afferent inhibition (LAI) of the median nerve in RLS patients was decreased significantly at ISIs of 150 (p = 0.000) and 200 ms (p = 0.004). Upon peroneal nerve stimulation, no significant difference was observed between the two groups at any ISI.

Conclusions: Our results suggest increased motor cortical excitability of the legs and disturbed sensorimotor integration in RLS patients; this disturbance might originate at the cortical level.

Lack of Association Between Shape and Volume of Subcortical Brain Structures and Restless Legs Syndrome

Objective

Previous studies on patients with restless legs syndrome (RLS) yielded inconclusive results in the magnetic resonance imaging (MRI)-based analyses of alterations of subcortical structures in the brain. The aim of this study was to compare volumes as well as shapes of subcortical structures and the hippocampus between RLS cases and controls. Additionally, the associations between the genetic risks for RLS and subcortical volumes were investigated.

Methods

We compared volumetric as well as shape differences assessed by 3 T MRI in the caudate nucleus, hippocampus, globus pallidus, putamen, and thalamus in 39 RLS cases versus 117 controls, nested within a population-based sample. In a subsample, we explored associations between known genetic risk markers for RLS and the volumes of the subcortical structures and the hippocampus.

Results

No significant differences between RLS cases and controls in subcortical and hippocampal shapes and volumes were observed. Furthermore, the genetic risk for RLS was unrelated to any alterations of subcortical and hippocampal gray matter volume.

Interpretation

We conclude that neither RLS nor the genetic risk for the disease give rise to changes in hippocampal and subcortical shapes and gray matter volumes.

Haste makes waste: Decision making in patients with restless legs syndrome with and without augmentation

Objectives

To investigate decision making in patients with primary restless legs syndrome (RLS) with and without augmentation treated with dopaminergic medication.

Methods

A total of 64 non-demented RLS patients treated with dopaminergic medication with and without augmentation were included in this study. We used an information sampling task to assess how much evidence participants gather before making a decision. Performance was compared to the results of 21 healthy controls.

Results

All patients with and without augmentation gathered less information than healthy controls before making a decision (p<0.001), but there was no difference between the two patient groups (p = 1.0). Furthermore, both patient groups made more irrational decisions (e.g. decisions against the evidence they had at the time) than healthy controls (p≤0.002). In addition, RLS patients with augmentation made significantly more irrational decisions than RLS patients without augmentation (p = 0.037) and controls (p<0.001).

Conclusions

Our results show that RLS patients treated with dopaminergic drugs, regardless of having augmentation or not, jumped to conclusions and decided significantly more often against the evidence they had at the time of their decision. However, those with augmentation performed worse than all other groups and made more often irrational decisions, a phenomenon which is also common in patients with substance abuse or behavioural addictions. Thus, jumping to conclusions and deciding with a higher degree of uncertainty as well as irrational decision making is more common in RLS patients treated with dopaminergic medication particularly in those with augmentation.

Brain imaging and networks in restless legs syndrome

Several studies provide information useful to our understanding of restless legs syndrome (RLS), using various imaging techniques to investigate different aspects putatively involved in the pathophysiology of RLS, although there are discrepancies between these findings. The majority of magnetic resonance imaging (MRI) studies using iron-sensitive sequences supports the presence of a diffuse, but regionally variable low brain-iron content, mainly at the level of the substantia nigra, but there is increasing evidence of reduced iron levels in the thalamus. Positron emission tomography (PET) and single positron emission computed tomography (SPECT) findings mainly support dysfunction of dopaminergic pathways involving not only the nigrostriatal but also mesolimbic pathways. None or variable brain structural or microstructural abnormalities have been reported in RLS patients; reports are slightly more consistent concerning levels of white matter. Most of the reported changes were in regions belonging to sensorimotor and limbic/nociceptive networks. Functional MRI studies have demonstrated activation or connectivity changes in the same networks. The thalamus, which includes different sensorimotor and limbic/nociceptive networks, appears to have lower iron content, metabolic abnormalities, dopaminergic dysfunction, and changes in activation and functional connectivity. Summarizing these findings, the primary change could be the reduction of brain iron content, which leads to dysfunction of mesolimbic and nigrostriatal dopaminergic pathways, and in turn to a dysregulation of limbic and sensorimotor networks. Future studies in RLS should evaluate the actual causal relationship among these findings, better investigate the role of neurotransmitters other than dopamine, focus on brain networks by connectivity analysis, and test the reversibility of the different imaging findings following therapy.

Restless Legs Syndrome: Current Concepts about Disease Pathophysiology

Background

In the past few decades, much has been learned about the pathophysiology of restless legs syndrome (RLS). Investigators have studied neuropathology, imaging, electrophysiology, and genetics of RLS, identifying brain regions and biological systems affected in RLS. This manuscript will review RLS pathophysiology literature, examining the RLS state through consideration of the neuroanatomy, then the biological, organ, and genetic systems.

Methods

Pubmed (1966 to April 2016) was searched for the term “restless legs syndrome” cross-referenced with “pathophysiology,” “pathogenesis,” “pathology,” or “imaging.” English language papers were reviewed. Studies that focused on RLS in relation to another disease were not reviewed.

Results

Although there are no gross structural brain abnormalities in RLS, widespread brain areas are activated, including the pre- and post-central gyri, cingulate cortex, thalamus, and cerebellum. Pathologically, the most consistent finding is striatal iron deficiency in RLS patients. A host of other biological systems are also altered in RLS, including the dopaminergic, oxygen-sensing, opioid, glutamatergic, and serotonergic systems. Polymorphisms in genes including BTBD9 and MEIS1 are associated with RLS.

Discussion

RLS is a neurologic sensorimotor disorder that involves pathology, most notably iron deficiency, in motor and sensory brain areas. Brain areas not subserving movement or sensation such as the cingulate cortex and cerebellum are also involved. Other biological systems including the dopaminergic, oxygen-sensing, opioid, glutamatergic, and serotonergic systems are involved. Further research is needed to determine which of these anatomic locations or biological systems are affected primarily, and which are affected in a secondary response.

Patterns of increased intrinsic functional connectivity in patients with restless legs syndrome are associated with attentional control of sensory inputs

INTRODUCTION

Potential alterations of intrinsic functional connectivity in idiopathic restless legs syndrome (RLS) are to be assumed since RLS is considered a network disorder. Whole-brain-based investigation of intrinsic functional connectivity networks including the sensorimotor systems in patients with RLS was compared with matched healthy controls.

METHODS

'Resting-state' functional MRI (1.5 T) from 26 patients with RLS and 26 matched controls were analyzed using standardized seed-based analysis procedures. The motor/sensorimotor, sensory thalamic, ventral and dorsal attention, basal ganglia-thalamic, cingulate, and brainstem networks were used for voxel-based group comparisons between RLS patients and controls.

RESULTS

Significantly increased connectivities were observed in the sensory thalamic, ventral and dorsal attention, basal ganglia-thalamic, and cingulate networks in RLS patients, whereas no differences could be demonstrated for the motor/sensorimotor and the brainstem system. The pattern of functional connectivity alterations was positively correlated with increasing symptom severity.

CONCLUSIONS

Abnormally increased regional BOLD synchronization appears to be a key feature of intrinsic brain architecture in RLS. Alterations in cortical and sub-cortical functional networks support the notion that the underlying pathophysiology of RLS is beyond the sensorimotor and the brainstem system and may be also associated with altered attentional control of sensory inputs.

Microstructure of the Midbrain and Cervical Spinal Cord in Idiopathic Restless Legs Syndrome: A Diffusion Tensor Imaging Study

STUDY OBJECTIVES

Diffusion tensor imaging (DTI) allows the study of white matter microstructure in the central nervous system. The aim of this study was to examine the DTI metrics of the cervical spinal cord and the brainstem up to the midbrain in patients with idiopathic restless legs (RLS) compared to matched healthy controls.

METHODS

DTI analysis of the cervical spinal cord and the brainstem up into the midbrain was performed in 25 patients with idiopathic RLS and 25 matched healthy controls. Data analysis in the brain was performed by voxelwise comparison of fractional anisotropy (FA) maps at group level. Cervical spinal cord data analysis was performed by slicewise analysis of averaged FA values in axial slices along the spinal cord.

RESULTS

Voxelwise comparison of FA maps in the brainstem showed significant microstructural alterations in two clusters in the midbrain bilaterally. Slicewise comparison of the FA maps in the cervical spinal cord showed a trend for lower FA values at the level of the second and third vertebra area in the patient sample.

CONCLUSIONS

The imaging data suggest that significant alterations in the midbrain in RLS can be visualized by DTI and might correlate to a macroscopically subtle process with changes of the tissue microstructure in the corresponding tracts. An additional area of interest is regionally clustered in the upper cervical spinal cord with a tendency toward altered diffusion metrics. These results might be addressed by further studies, e.g., at higher magnetic field strengths.

Restless Leg Syndrome/Willis-Ekbom Disease Pathophysiology

Restless leg syndrome/Willis-Ekbom disease has brain iron deficiency that produces excessive dopamine and known genetic risks, some of which contribute to the brain iron deficiency. Dopamine treatments work temporarily but may eventually produce further postsynaptic down-regulation and worse restless leg syndrome. This article includes sections focused on pathophysiologic findings from each of these areas: genetics, cortical-spinal excitability, and iron and dopamine.

Neuroimaging in Restless Legs Syndrome

Neuroimaging studies are of crucial relevance in defining the pathophysiology of restless legs syndrome (RLS). MRI studies showed no structural brain lesions and confirmed a central iron deficiency. Structural and functional studies showed an involvement of the thalamus, sensorimotor cortical areas, and cerebellum in RLS and assessed neurotransmission abnormalities in the dopaminergic and opiate systems. Finally, glutamatergic hyperactivity has been proposed as a cause of disrupted and shortened sleep in RLS. Differences among the results of the studies make it difficult to draw any definitive conclusions, thus, suggesting the need for future research.