T2 relaxometry using 3.0-tesla magnetic resonance imaging of the brain in early- and late-onset restless legs syndrome

Iron Deficiency and Sleep/Wake Behaviors: A Scoping Review of Clinical Practice Guidelines-How to Overcome the Current Conundrum?

Current evidence suggests that iron deficiency (ID) plays a key role in the pathogenesis of conditions presenting with restlessness such as attention deficit hyperactivity disorder (ADHD) and restless legs syndrome (RLS). In clinical practice, ID and iron supplementation are not routinely considered in the diagnostic work-up and/or as a treatment option in such conditions. Therefore, we conducted a scoping literature review of ID guidelines. Of the 58 guidelines included, only 9 included RLS, and 3 included ADHD. Ferritin was the most frequently cited biomarker, though cutoff values varied between guidelines and depending on additional factors such as age, sex, and comorbidities. Recommendations surrounding measurable iron biomarkers and cutoff values varied between guidelines; moreover, despite capturing the role of inflammation as a concept, most guidelines often did not include recommendations for how to assess this. This lack of harmonization on the interpretation of iron and inflammation biomarkers raises questions about the applicability of current guidelines in clinical practice. Further, the majority of ID guidelines in this review did not include the ID-associated disorders, ADHD and RLS. As ID can be associated with altered movement patterns, a novel consensus is needed for investigating and interpreting iron status in the context of different clinical phenotypes.

Change of iron content in brain regions after intravenous iron therapy in restless legs syndrome: quantitative susceptibility mapping study

STUDY OBJECTIVES

The pathomechanism of restless legs syndrome (RLS) is related to brain iron deficiency and iron therapy is effective for RLS; however, the effect of iron therapy on human brain iron state has never been studied with magnetic resonance imaging. This study aimed to investigate the change of brain iron concentrations in patients with RLS after intravenous iron therapy using quantitative susceptibility mapping (QSM).

METHODS

We enrolled 31 RLS patients and 20 healthy controls. All participants underwent initial baseline (t0) assessment using brain magnetic resonance imaging, serum iron status, and sleep questionnaires including international RLS Study Group rating scale (IRLS). RLS patients underwent follow-up tests at 6 and 24 weeks (t1 and t2) after receiving 1000 mg ferric carboxymaltose. Iron content of region-of-interest on QSM images was measured for 13 neural substrates using the fixed-shaped method.

RESULTS

RLS symptoms evaluated using IRLS were significantly improved after iron treatment (t0: 29.7 ± 6.5, t1: 19.5 ± 8.5, t2: 21.3 ± 10.1; p < .001). There was no significant difference in susceptibility values between the controls and RLS patients at t0. In the caudate nucleus, putamen, and pulvinar thalamus of RLS patients, the QSM values differed significantly for three timepoints (p = .035, .048, and .032, respectively). The post-hoc analysis revealed that the QSM values increased at t1 in the caudate nucleus (66.8 ± 18.0 vs 76.4 ± 16.6, p = .037) and decreased from t1 to t2 in the putamen (69.4 ± 16.3 vs 62.5 ± 13.6, p = .025). Changes in the QSM values for the pulvinar and caudate nuclei at t1 were positively and negatively correlated with symptomatic improvement, respectively (r = 0.361 and -0.466, respectively).

CONCLUSIONS

Intravenous iron treatment results in changes in brain iron content which correlate to reductions in RLS severity. This suggests a connection between symptom improvement and the associated specific brain regions constituting the sensorimotor network.

Putative Animal Models of Restless Legs Syndrome: A Systematic Review and Evaluation of Their Face and Construct Validity

Restless legs syndrome (RLS) is a sensorimotor disorder that severely affects sleep. It is characterized by an urge to move the legs, which is often accompanied by periodic limb movements during sleep. RLS has a high prevalence in the population and is usually a life-long condition. While its origins remain unclear, RLS is initially highly responsive to treatment with dopaminergic agonists that target D2-like receptors, in particular D2 and D3, but the long-term response is often unsatisfactory. Over the years, several putative animal models for RLS have been developed, mainly based on the epidemiological and neurochemical link with iron deficiency, treatment efficacy of D2-like dopaminergic agonists, or genome-wide association studies that identified risk factors in the patient population. Here, we present the first systematic review of putative animal models of RLS, provide information about their face and construct validity, and report their role in deciphering the underlying pathophysiological mechanisms that may cause or contribute to RLS. We propose that identifying the causal links between genetic risk factors, altered organ functions, and changes to molecular pathways in neural circuitry will eventually lead to more effective new treatment options that bypass the side effects of the currently used therapeutics in RLS, especially for long-term therapy.

Sleep medicine: Practice, challenges and new frontiers

Sleep medicine is an ambitious cross-disciplinary challenge, requiring the mutual integration between complementary specialists in order to build a solid framework. Although knowledge in the sleep field is growing impressively thanks to technical and brain imaging support and through detailed clinic-epidemiologic observations, several topics are still dominated by outdated paradigms. In this review we explore the main novelties and gaps in the field of sleep medicine, assess the commonest sleep disturbances, provide advices for routine clinical practice and offer alternative insights and perspectives on the future of sleep research.

Huzursuz bacak sendromunun kan parametreleri ile olan ilişkisi

sağlıklı kontrol grubu ile bazı laboratuvar parametreleri açısından karşılaştırarak etyopatogenezi etkileyen faktörleri araştırmak amaçlanmıştır. Gereç ve Yöntem: Huzursuz bacak sendromu tanısı konulan hastalar çalışmaya dahil edildi. Yaş ve cinsiyet açısından benzer kontrol grubu oluşturuldu. Her iki grup demir, ferritin, demir bağlama kapasitesi, folat, vitamin B12, vitamin D, kalsiyum, magnezyum, ALT, AST, hemogram, kreatinin, açlık kan şekeri, tiroid hormon seviyeleri açısından karşılaştırıldı. Bulgular: Çalışmaya 37 huzursuz bacak sendromu hastası, 41 tane de kontrol dahil edildi. Huzursuz bacak sendromu grubunda hemoglobin, ferritin, demir, açlık kan şekeri, D vitamini ve fT4 değerleri sırasıyla 12.7 (10.3-16.0) g/dL, 37.3 (3.7-89.4) mg/L, 62 (21-195) μg/dL, 96 (65-250) mg/L, 11.26 (4.20-41.57) ug/L ve 1.24 (0.73-2.14) µg/dL iken kontrol grubunda sırasıyla 14.8 (12.3-16.1) g/dL, 56 (9-189) mg/L, 90 (30-245) µg/dL, 91 (70-107) mg/L, 17.31 (5.73-32.90) µg/L ve 1.08 (0.63-2.04) µg/dL idi. Hemoglobin, ferritin, demir, açlık kan şekeri, vitamin D ve T4 seviyeleri açısından gruplar arasında istatistiksel olarak anlamlı farklılıklar saptandı. Sonuç: Huzursuz bacak sendromlu hastalarda hemoglobin ve demir parametreleri, vitamin D düzeyleri, açlık kan şekeri ve T4 seviyeleri eksiklikleri açısından mutlaka değerlendirilmeli, gereklilik halinde mutalaka replase edilmelidir. Eksikliklerin düzeltilmesi hastaların klinikleri açısından yararlı olabilir.

Revisiting brain iron deficiency in restless legs syndrome using magnetic resonance imaging

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Increased iron in RLS was found in the caudate, putamen and red nucleus.

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A meta-analysis revealed no significant evidence of reduced iron in RLS as assessed by MRI.

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Evidence suggestive of publication bias for results on the substantia nigra was found.

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Our results support the view that brain iron mobilization or homeostasis is impaired in RLS.

Study objectives

Studies on brain iron content in restless legs syndrome (RLS) using magnetic resonance imaging (MRI) are heterogeneous. In this study, we sought to leverage the availability of a large dataset including a range of iron-sensitive MRI techniques to reassess the association between brain iron content and RLS with added statistical power and to compare these results to previous studies.

Methods

The relaxation rates R₂, R₂′, and R₂* and quantitative susceptibility are MRI parameters strongly correlated to iron content. In general, these parameters are sensitive to magnetic field variations caused by iron particles. These parameters were quantified within iron-rich brain regions using a fully automatized approach in a cohort of 72 RLS patients and individually age and gender-matched healthy controls identified from an existing dataset acquired at the Sleep Laboratory of the Department of Neurology, Medical University of Innsbruck. 3 T-MRI measures were corrected for age and volume of the segmented brain nuclei and results were compared with previous findings in a meta-analysis.

Results

In our cohort, RLS patients had increased R₂* signal in the caudate and increased quantitative susceptibility signal in the putamen and the red nucleus compared to controls, suggesting increased iron content in these areas. The meta-analysis revealed no significant pooled effect across all brain regions. Furthermore, potential publication bias was identified for the substantia nigra.

Conclusions

Normal and increased iron content of subcortical brain areas detected in this study is not in line with the hypothesis of reduced brain iron storage, but favors CSF investigations and post mortem studies indicating alteration of brain iron mobilization and homeostasis in RLS.

Thalamic Deep Brain Stimulation May Improve Restless Legs Syndrome in Patients With Essential Tremor

OBJECTIVES

To determine change in restless legs syndrome (RLS) symptoms in essential tremor (ET) patients undergoing bilateral thalamic ventral intermedius (VIM) deep brain stimulation (DBS) surgery.

MATERIALS AND METHODS

We retrospectively reviewed our database of ET patients with RLS who had undergone VIM DBS for tremor from 2012 to 2020. We reviewed the patients with available International Restless Leg Syndrome Study Group RLS scale scores before and after DBS. Percentage of responders, defined as proportion of patients experiencing three or more point improvement of RLS scores post-DBS, was calculated. We performed two-tailed t-test of pre-DBS and post-DBS RLS scores.

RESULTS

We identified 13 patients with ET and RLS who had undergone bilateral VIM DBS, of whom nine (69%) were responders post-DBS. Five of 13 patients (38%) had complete resolution of RLS post-DBS. For all patients, mean pre-DBS RLS score was 15.8 ± 7.9 which improved by 46% post-DBS to a mean of 8.5 ± 8.8 (p = 0.007). Four patients rated their RLS scale one night with the stimulator OFF and another night with the stimulator ON. The mean RLS score with stimulator ON was 15.5 ± 7.6 which improved by 53% to a mean of 6.25 ± 7.8 (p = 0.008), with two having complete resolution of RLS with stimulator ON. Of the nine responders, six preferred to keep their stimulator ON at night due to relief of RLS and better subjective quality of sleep.

CONCLUSIONS

We report for the first time improvement of RLS in patients with ET after bilateral thalamic DBS. Although many ET patients with nonrechargeable DBS systems switch off their stimulator at night to conserve battery life, those with RLS may potentially benefit from keeping their stimulator ON at night to relieve their RLS.

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.

Pharmacologic Treatment of Restless Legs Syndrome

Restless legs syndrome (RLS)/Willis-Ekbom disease is a neurologic disorder characterized by a strong desire to move when at rest (usually in the evening) and paraesthesia in their lower legs. The most widely used therapies for first-line treatment of RLS are dopaminergic drugs; however, their long-term use can lead to augmentation. α2δ Ligands, opioids, iron, glutamatergic drugs, adenosine, and sleep aids have been investigated as alternatives. The pathogenesis of RLS is not well understood. Despite the efficacy of dopaminergic drugs in the treatment of this disorder, unlike in Parkinson's disease dopaminergic cell loss in the substantia nigra has not been observed in RLS. The etiology of RLS is likely complex, involving multiple neural pathways. RLS-related genes identified in genome-wide association studies can provide insight into the mechanistic basis and pathophysiology of RLS. Here we review the current treatments and knowledge of the mechanisms underlying RLS.

Restless Legs Syndrome and Other Common Sleep-Related Movement Disorders

PURPOSE OF REVIEW

In this article, the different sleep-related movement disorders are discussed with special attention given to restless legs syndrome (RLS).

RECENT FINDINGS

The differential diagnosis of sleep-related movement disorders can often be challenging; therefore, it is essential to have accurate information to make a correct diagnosis. This article focuses on RLS, highlighting the change in the paradigm of initial treatment, the role played by iron (pathophysiologic and therapeutic), and how to approach possible complications occurring with long-term treatment.

SUMMARY

RLS is one of the most common neurologic conditions, and it is common in clinical practice to find patients experiencing symptoms suggestive of RLS. Neurologists must be careful and thorough in the diagnosis, excluding RLS mimics. The decisions regarding which specific sleep-related movement disorder is present and how it should be treated are important because in certain cases, especially in RLS, adverse effects and long-term complications are frequently reported with the use of certain drugs.

Different iron deposition patterns in hemodialysis patients with and without restless legs syndrome: a quantitative susceptibility mapping study

OBJECTIVE

Brain iron deposition in hemodialysis (HD) patients increases over time. Iron deficiency in gray matter nuclei has been reported to lead to idiopathic restless legs syndrome (RLS) symptoms. Regardless of unpleasant RLS sensations, the patterns of iron deposition between hemodialysis patients with RLS (HD-RLS) and hemodialysis patients without RLS (HD-nRLS) are still unclear. To evaluate the differences in iron deposition patterns between HD-RLS and HD-nRLS patients, we utilized quantitative susceptibility mapping (QSM).

METHODS

In sum, 24 HD-RLS patients, 25 HD-nRLS patients and 30 age- and sex-matched healthy controls (HCs) were enrolled. The QSM was used to assess susceptibility values of the regions of interest (ROIs), including the caudate nucleus (CN), putamen (PUT), globus pallidus (GP), thalamus (THA), substantia nigra (SN), red nucleus (RN) and dentate nucleus (DN).

RESULTS

HD duration was significantly longer in HD-RLS patients than in HD-nRLS patients (P < 0.05). The susceptibility of HD-RLS and HD-nRLS patients in PUT was higher than that in HCs (P < 0.05), illustrating elevated iron content in the nucleus. Compared with HD-nRLS patients, HD-RLS patients demonstrated reduced susceptibility in CN and PUT (both P < 0.05). Compared with HCs, HD-RLS patients displayed decreased susceptibility in DN (P < 0.05).

CONCLUSIONS

Different iron deposition patterns between HD-RLS and HD-nRLS patients in PUT and DN, which further support disturbed sensory processing in RLS, may be involved in RLS pathogenesis in HD patients.

Multimodal Magnetic Resonance Imaging reveals alterations of sensorimotor circuits in restless legs syndrome

Study Objectives

Integrated information on brain microstructural integrity and iron storage and its impact on the morphometric profile is not available in restless legs syndrome (RLS). We applied multimodal magnetic resonance imaging (MRI) including diffusion tensor imaging, the transverse relaxation rate (R2*), a marker for iron storage, as well as gray and white matter volume measures to characterize RLS-related MRI signal distribution patterns and to analyze their associations with clinical parameters.

Methods

Eighty-seven patients with RLS (mean age 51, range 20–72 years; disease duration, mean 13 years, range 1–46 years, of those untreated n = 30) and 87 healthy control subjects, individually matched for age and gender, were investigated with multimodal 3T MRI.

Results

Volume of the white matter compartment adjacent to the post- and precentral cortex and fractional anisotropy (FA) of the frontopontine tract were both significantly reduced in RLS compared to healthy controls, and these alterations were associated with disease duration (r = 0.25, p = 0.025 and r = 0.23, p = 0.037, respectively). Corresponding gray matter volume increases of the right primary motor cortex in RLS (p &lt; 0.001) were negatively correlated with the right FA signal of the frontopontine tract (r = −0.22; p &lt; 0.05). Iron content evaluated with R2* was reduced in the putamen as well as in temporal and occipital compartments of the RLS cohort compared to the control group (p &lt; 0.01).

Conclusions

Multimodal MRI identified progressing white matter decline of key somatosensory circuits that may underlie the perception of sensory leg discomfort. Increases of gray matter volume of the premotor cortex are likely to be a consequence of functional neuronal reorganization.

Caenorhabditis elegans and its applicability to studies on restless legs syndrome

Restless legs syndrome (RLS) is a common neurological disorder in the United States. This disorder is characterized by an irresistible urge to move the legs, although the symptoms vary in a wide range. The pathobiology of RLS has been linked to iron (Fe) deficiency and dopaminergic (DAergic) dysfunction. Several genetic factors have been reported to increase the risk of RLS. Caenorhabditis elegans (C. elegans) is a well-established animal model with a fully sequenced genome, which is highly conserved with mammals. Given the detailed knowledge of its genomic architecture, ease of genetic manipulation and conserved biosynthetic and metabolic pathways, as well as its small size, ease of maintenance, speedy generation time and large brood size, C. elegans provides numerous advantages in studying RLS-associated gene-environment interactions. Here we will review current knowledge about RLS symptoms, pathology and treatments, and discuss the application of C. elegans in RLS study, including the worm homologous genes and methods that could be performed to advance the pathophysiology RLS.

Comorbidities, treatment, and pathophysiology in restless legs syndrome

Restless legs syndrome, also known as Willis-Ekbom disease, is a common neurological condition whose manifestation is affected by complex environmental and genetic interactions. Restless legs syndrome can occur on its own, mostly at a young age, or with comorbidities such as cardiovascular disease, diabetes, and arterial hypertension, making it a difficult condition to properly diagnose. However, the concept of restless legs syndrome as being two entities, primary or secondary to another condition, has been challenged with genetic data providing further insight into the pathophysiology of the condition. Although dopaminergic treatment was formerly the first-line therapy, prolonged use can result in a serious worsening of symptoms known as augmentation. Clinical studies on pregabalin, gabapentin enacarbil, oxycodone-naloxone, and iron preparations have provided new treatment options, but most patients still report inadequate long-term management of symptoms. Studies of the hypoxic pathway activation and iron deficiency have provided valuable information about the pathophysiology of restless legs syndrome that should now be translated into new, more effective treatments for restless legs syndrome.

Restless Legs Syndrome and Parkinson Disease: A Causal Relationship Between the Two Disorders?

Restless Legs Syndrome/Willis-Ekbom Disease (RLS/WED) is a common sleep related movement disorder that can be idiopathic or occurs in comorbidity with other medical conditions such as polyneuropathy, iron deficiency anemia, multiple sclerosis, hypertension and cardiovascular diseases. In recent years, a growing body of literature investigated the association between RLS/WED and Parkinson's Disease (PD). Several questions regarding the comorbidity between these two disorders are still unanswered. If the insurgence of RLS/WED may precede the onset of PD, or if RLS/WED could represent a secondary condition of PD and if impaired dopaminergic pathway may represent a bridge between these two conditions are still debatable issues. In this review, we critically discuss the relationship between RLS/WED and PD by reviewing cross sectional and longitudinal studies, as well as the role of dopamine in these disorders. A twofold interpretation have to be taken into account: dopaminergic therapy may have a crucial role in the development of RLS/WED in PD patients or RLS/WED can be conceived as an early manifestation of PD rather than a risk factor. Several studies showed a high prevalence of RLS/WED in PD patients and several findings related to dopaminergic and iron alterations in both disorders, however up to now it is difficult to find a point of agreement between studies. A greater number of systematic and strongly controlled longitudinal studies as well as basic pathophysiological investigations particularly in RLS/WED are needed to clarify this complex relationship.

Chronic back pain cured by low-dose levodopa: is it a variant of restless legs syndrome?

Chronic back pain is one of the most common reasons for missed work and visits to the doctor. This report presents 2 interesting cases of chronic back pain that were effectively relieved by low-dose levodopa. These 2 patients showed no sign of anatomical problem of the spine or relative structures, but the discomforts on the back manifested some characteristics resembling those in restless legs syndrome (RLS), and one of them actually developed RLS after many years of back problem. We believe that this type of chronic back pain might be a variant of RLS, which we would like to call "restless back", and it can be effectively treated by dopaminergic drugs.

Restless Legs Syndrome: From Pathophysiology to Clinical Diagnosis and Management

Restless legs syndrome (RLS), a common neurological sensorimotor disorder in western countries, has gained more and more attention in Asian countries. The prevalence of RLS is higher in older people and females. RLS is most commonly related to iron deficiency, pregnancy and uremia. The RLS symptoms show a significant circadian rhythm and a close relationship to periodic limb movements (PLMs) in clinical observations, while the pathophysiological pathways are still unknown. The diagnostic criteria have been revised in 2012 to improve the validity of RLS diagnosis. Recent studies have suggested an important role of iron decrease of brain in RLS pathophysiology. Dopaminergic (DA) system dysfunction in A11 cell groups has been recognized long ago from clinical treatment and autopsy. Nowadays, it is believed that iron dysfunction can affect DA system from different pathways and opioids have a protective effect on DA system. Several susceptible single nucleotide polymorphisms such as BTBD9 and MEIS1, which are thought to be involved in embryonic neuronal development, have been reported to be associated with RLS. Several pharmacological and non-pharmacological treatment are discussed in this review. First-line treatments of RLS include DA agents and α2δ agonists. Augmentation is very common in long-term treatment of RLS which makes prevention and management of augmentation very important for RLS patients. A combination of different types of medication is effective in preventing and treating augmentation. The knowledge on RLS is still limited, the pathophysiology and better management of RLS remain to be discovered.

Central and peripheral nervous system excitability in restless legs syndrome

Neurophysiological techniques have been applied in restless legs syndrome (RLS) to obtain direct and indirect measures of central and peripheral nervous system excitability, as well as to probe different neurotransmission pathways. Data converge on the hypothesis that, from a pure electrophysiological perspective, RLS should be regarded as a complex sensorimotor disorder in which cortical, subcortical, spinal cord, and peripheral nerve generators are all involved in a network disorder, resulting in an enhanced excitability and/or decreased inhibition. Although the spinal component may have dominated in neurophysiological assessment, possibly because of better accessibility compared to the brainstem or cerebral components of a hypothetical dysfunction of the diencephalic A11 area, multiple mechanisms, such as reduced central inhibition and abnormal peripheral nerve function, contribute to the pathogenesis of RLS similarly to some chronic pain conditions. Dopamine transmission dysfunction, either primary or triggered by low iron and ferritin concentrations, may also bridge the gap between RLS and chronic pain entities. Further support of disturbed central and peripheral excitability in RLS is provided by the effectiveness of nonpharmacological tools, such as repetitive transcranial magnetic stimulation and transcutaneous spinal direct current stimulation, in transiently modulating neural excitability, thereby extending the therapeutic repertoire. Understanding the complex interaction of central and peripheral neuronal circuits in generating the symptoms of RLS is mandatory for a better refinement of its therapeutic support.

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.

Brain iron deficiency in idiopathic restless legs syndrome measured by quantitative magnetic susceptibility at 7 tesla

OBJECTIVES

Altered brain iron homeostasis with regional iron deficiency has been previously reported in several studies of restless legs syndrome (RLS) patients. Inconsistencies still exist, however, in the reported iron changes in different brain regions and different RLS phenotypes. The purpose of this study was to assess differences in brain iron concentrations between RLS patients and healthy controls and their relation to severity of disease and periodic limb movement during sleep (PLMS).

METHODS

Assessment of brain iron was done using quantitative magnetic susceptibility measurement, which has been shown to correlate well with the tissue iron content in brain's gray matter. Thirty-nine RLS patients and 29 age-matched healthy controls were scanned at 7 T. Magnetic susceptibilities in substantia nigra (SN), thalamus, striatum, and several iron-rich gray matter regions were quantified and compared with related clinical measures.

RESULTS

Compared with healthy controls, RLS patients showed significantly decreased magnetic susceptibility in the thalamus and dentate nucleus. No significant difference was found in the SN between RLS patients and healthy controls, but a significant correlation was observed between magnetic susceptibility in SN and the PLMS measure.

CONCLUSIONS

Using quantitative magnetic susceptibility as an in vivo indicator of brain iron content, the present study supports the general hypothesis of brain iron deficiency in RLS and indicates its possible link to PLMS.

Restless Legs Syndrome and Leg Motor Restlessness in Parkinson's Disease

Sleep disturbances are important nonmotor symptoms in Parkinson's disease (PD) that are associated with a negative impact on quality of life. Restless legs syndrome (RLS), which is characterized by an urge to move the legs accompanied by abnormal leg sensations, can coexist with PD, although the pathophysiology of these disorders appears to be different. RLS and PD both respond favorably to dopaminergic treatment, and several investigators have reported a significant relationship between RLS and PD. Sensory symptoms, pain, motor restlessness, akathisia, and the wearing-off phenomenon observed in PD should be differentiated from RLS. RLS in PD may be confounded by chronic dopaminergic treatment; thus, more studies are needed to investigate RLS in drug-naïve patients with PD. Recently, leg motor restlessness (LMR), which is characterized by an urge to move the legs that does not fulfill the diagnostic criteria for RLS, has been reported to be observed more frequently in de novo patients with PD than in age-matched healthy controls, suggesting that LMR may be a part of sensorimotor symptoms intrinsic to PD. In this paper, we provide an overview of RLS, LMR, and PD and of the relationships among these disorders.

Heme Oxygenase-1 and 2 Common Genetic Variants and Risk for Restless Legs Syndrome

Several neurochemical, neuropathological, neuroimaging, and experimental data, suggest that iron deficiency plays an important role in the pathophysiology of restless legs syndrome (RLS). Heme-oxygenases (HMOX) are an important defensive mechanism against oxidative stress, mainly through the degradation of heme to biliverdin, free iron, and carbon monoxide. We analyzed whether HMOX1 and HMOX2 genes are related with the risk to develop RLS.We analyzed the distribution of genotypes and allelic frequencies of the HMOX1 rs2071746, HMOX1 rs2071747, HMOX2 rs2270363, and HMOX2 rs1051308 SNPs, as well as the presence of Copy number variations (CNVs) of these genes in 205 subjects RLS and 445 healthy controls.The frequencies of rs2071746TT genotype and rs2071746T allelic variant were significantly lower in RLS patients than that in controls, although the other 3 studied SNPs did not differ between RLS patients and controls. None of the studied polymorphisms influenced the disease onset, severity of RLS, family history of RLS, serum ferritin levels, or response to dopaminergic agonist, clonazepam or GABAergic drugs.The present study suggests a weak association between HMOX1 rs2071746 polymorphism and the risk to develop RLS in the Spanish population.

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.