White matter hyperintensities on brain magnetic resonance imaging: comparison of early-onset and late-onset restless legs syndrome

Unraveling the pathophysiology of restless legs syndrome from multimodal MRI techniques: A systematic review

BACKGROUND

Restless Legs Syndrome (RLS) is a common neurological disorder currently diagnosed based on clinical features only, and characterized by a compulsive urge to move the legs triggered by rest or diminished arousal. This systematic review aimed at integrating all current brain magnetic resonance imaging (MRI) modalities for a convergent pathophysiological understanding of RLS phenomenology.

METHODS

We performed a MEDLINE (PubMed)-based systematic review for research articles in patients with primary RLS published in English from 2010 till November 2023. Studies meeting the inclusion criteria according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses criteria were systematically assessed for quality using modality-specific checklists, bias using AXIS tool and a narrative synthesis of the results was conducted.

RESULTS

A total of 49 studies (22 structural, 12 DTI, 7 iron-imaging, 4 spectroscopy with 10 datasets combining multiple approaches) involving 1273 patients (414 males) and 1333 healthy controls (478 males) met the eligibility criteria. Despite participant, technical/device-related and statistical heterogeneity, most agree that patients with primary RLS have structural and metabolite alterations, changes in multiple white matter tract architectures, and disrupted functional connectivity within multiple brain areas. Most of the studies (n = 43, 88 %) have a low-risk of bias on the AXIS scale. Scores on the modality-specific checklist ranged from 46 to 92 %, 70-93 % and 54-92 % for structural MRI, DTI and MRS Datasets, respectively.

CONCLUSIONS

Notwithstanding the large heterogeneity in the methods employed, global connectivity alterations suggest the utility of casting RLS within a system-level perspective rather than viewing it as related to the dysfunction of a single or particular brain region. A holistic approach and its integration within the framework of molecular vulnerability and neurotransmitter alterations are warranted to disentangle the complex pathophysiology of RLS and to identify new therapeutic targets.

Small vessel disease in patients with restless legs syndrome evidenced by elevated peak width of skeletonized mean diffusivity

Peak width of skeletonized mean diffusivity (PSMD) is a novel marker of small vessel disease. This study aimed to investigate small vessel disease in patients with restless legs syndrome (RLS) using PSMD. We prospectively enrolled 65 patients with primary RLS and 59 age- and sex-matched healthy controls. Diffusion tensor imaging (DTI) was performed using a 3-T magnetic resonance imaging scanner in patients with RLS and healthy controls. We obtained PSMD by DTI in several steps, including preprocessing, skeletonization, application of a custom mask, and histogram analysis. We compared the PSMD between patients with RLS and healthy controls and performed a correlation analysis between the PSMD and clinical characteristics in patients with RLS. The PSMD significantly differed between patients with RLS and healthy controls; it was higher in patients with RLS than that in healthy controls (2.423 vs. 2.298 × 10-4 mm2/s, p = 0.017). The PSMD significantly differed according to the RLS severity (2.305 × 10-4 mm2/s, moderate RLS; 2.368 × 10-4 mm2/s, severe RLS; 2.477 × 10-4 mm2/s, very severe RLS; p = 0.003). Additionally, the PSMD was positively correlated with age (r = 0.522, p < 0.001) and RLS severity (r = 0.263, p = 0.033). Patients with RLS exhibited a higher PSMD than that in healthy controls, indicating the evidence of small-vessel disease in RLS and that the severity increased as RLS severity increased. These findings provide crucial information for clinical management and treatment strategies, highlighting the importance of addressing small vessel disease in patients with RLS.

Exploring the pathophysiology of restless leg syndrome: focus on white matter structure and function

BACKGROUND

Restless legs syndrome (RLS) is a sleep disorder characterized by an irresistible urge to move the legs, with pathogenesis involving genetic, environmental, and neurobiological factors. Recent advancements in imaging techniques have provided valuable insights into the pathophysiological mechanisms of RLS.

OBJECTIVE

To synthesize recent research on white matter fiber alterations in RLS and their role in disease pathology.

MATERIALS AND METHODS

This review synthesized recent research on RLS, focusing on neuroimaging findings, particularly white matter fiber alterations, and their implications for disease mechanisms. Studies involving structural and functional MRI were analyzed.

RESULTS

Imaging studies suggested that RLS was associated with white matter integrity changes, affecting areas linked to sensory and motor control. These alterations may reflect disruptions in central nervous system pathways regulating movement.

CONCLUSION

White matter changes provide valuable insights into the pathophysiology of RLS, enhancing our understanding of the disorder and potentially guiding future therapeutic strategies.

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.

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.

Impaired endothelial function may predict treatment response in restless legs syndrome

While dopaminergic dysfunction is believed to be a crucial role in restless legs syndrome (RLS), changes in peripheral microvasculature system such as peripheral hypoxia and altered skin temperature, have been found. This study aimed to investigate whether patients with RLS would have a cerebral and peripheral endothelial dysfunction, and this may have association with treatment responsiveness. We evaluated cerebral endothelial function using breath-holding index (BHI) on transcranial Doppler in bilateral middle cerebral artery (MCA), posterior cerebral artery (PCA) and basilar artery (BA) and peripheral endothelial function using brachial flow-mediated dilation (FMD) in 34 patients with RLS compared with age and sex-matched controls. The values of BHI in both MCA and BA were significantly lower in RLS group than control group. The values of FMD also were significantly lower in RLS patients. There was a weak correlation between BHI and FMD (p = 0.038 in Rt MCA, p = 0.032 in Lt MCA, p = 0.362 in BA) in RLS, but not in controls. BHI differed according to treatment responsiveness. (p < 0.005). Our study suggests that RLS patients have poorer cerebral and peripheral endothelial function than controls, showing an underlying mechanism of RLS and further evidence of a possible association between RLS and cardiovascular disease.