Where is the core of the volcano? The undetermined origin of primary restless legs syndrome

Screening autonomic functions in patients with restless legs syndrome: A case-control study in a tertiary care hospital

PURPOSE

The clinical importance of autonomic involvement in patients with restless legs syndrome (RLS) remains unclear. To our knowledge, no study has explored the relationship between autonomic dysfunction and disease-related variables in patients with RLS. Therefore, this study aimed 1) to determine the presence of autonomic symptoms in drug-naïve patients with RLS in comparison with healthy controls using Scales for Outcomes in Parkinson's disease-Autonomic (SCOPA-AUT) questionnaire and 2) to evaluate the possible associations of autonomic dysfunction with clinical factors in RLS.

METHODS

A total of 70 drug-naïve patients with RLS and 85 healthy volunteers were enrolled. The SCOPA-AUT questionnaire and Epworth Sleepiness Scale (ESS) scores were used to determine autonomic functions and sleep propensity, respectively. Moreover, the International Restless Legs Syndrome Study Group rating scale was used to evaluate disease severity in the patient group.

RESULTS

Compared with the control group, the RLS group had significantly higher subscale scores (gastrointestinal, urinary, cardiovascular, thermoregulatory, pupillomotor, and sexual [women]) and total scores of the SCOPA-AUT questionnaire (p < 0.05). In the patient group, there was a significant correlation between the total scores and subscale scores (gastrointestinal, cardiovascular, and thermoregulatory subscales) of the SCOPA-AUT questionnaire and disease severity. Moreover, ESS was positively correlated with the total scores and subscale scores (urinary, cardiovascular, and pupillomotor) of the SCOPA-AUT questionnaire.

CONCLUSION

Disease severity and daytime sleepiness may be related to autonomic dysfunction in RLS. Further studies focusing on autonomic functions in RLS are required to improve management strategies and clinical outcomes.

TRIAL REGISTRATION

ClinicalTrials.gov. NCT04906486; May 28, 2021.

Electrophysiological findings in patients with restless legs syndrome

BACKGROUND

Restless legs syndrome (RLS) manifests as an urge to move the body to relieve the discomfortable sensations, primarily when resting, sitting, laying down, or sleeping. Diagnosis of RLS relies on clinical criteria, and the immobilization test was the only instrumental tool with equivocal results.

OBJECTIVES

To assess different electrophysiological findings in patients with RLS, and compare the diagnostic values of these parameters in the diagnosis of RLS.

METHODS

30 patients with primary RLS and 30 controls who were matched for age and gender were studied. Participant's demographics, laboratory findings, and electrophysiological test, namely nerve conduction studies (NCS), cutaneous silent period (CSP), H reflex and sympathetic skin response (SSR), F-wave latency, amplitude, F-wave duration (FWD), and the ratio between FWD and duration of the corresponding compound muscle action potential (FWD/CMAPD) were analyzed.

RESULTS

None of the patients showed altered NCS data. FWD of upper (12.37 ± 2.77 ms) and lower limb (21.71 ± 5.24 ms) were significantly longer in patients. Also, FWD/CMAP duration of the upper (1.03 ± 0.2) and lower limb (2.02 ± 0.55) was longer in patients. Likewise, they exhibited delayed CSP latency from TA (110.62 ± 13.73 ms) and APB (77.35 ± 12.16 ms) whereas the CSP duration from TA and APB was decreased (37.36 ± 11.59 ms; 42.55 ± 7.97 ms, respectively). The SSR latency was not different, and right-sided H reflex amplitude (5.07 ± 3.98 mV) and H/M ratio (0.65 ± 1.81) were significantly increased in the patient group.

CONCLUSION

The data suggest that there may be a dysfunction of the inhibitory/excitatory circuits at a spinal level; and no pathology in the peripheral nerves. The unilateral difference of H reflex amplitude and H/M ratio may suggest asymmetrical central inhibitory dysfunction. Further prospective studies with larger cohorts are now needed to evaluate the pathophysiology of RLS with different neurophysiological assessment tools.

A study for the mechanism of sensory disorder in restless legs syndrome based on magnetoencephalography

In spite of the relatively high incidence rate, the etiology and pathogenesis of restless legs syndrome (RLS) are still unclear. Long-term drug treatments fail to achieve satisfying curative effects, which is reflected by rebound and augmentation of related symptoms. An electrophysiological endophenotype experiment was done to investigate the mechanism of somatosensory disorder among RLS patients. Together with 15 normal subjects as the control group, with comparable ages and genders to the RLS patients, 15 primitive RLS patients were scanned by Magnetoencephalography (MEG) under natural conditions; furthermore, the somatosensory evoked magnetic field (SEF) with single and paired stimuli, was also measured. Compared to the control group, the SEF intensities of RLS patients' lower limbs were higher, and the paired-pulse depression (PPD) for SEF in RLS patients was attenuated. It was also revealed by time-frequency analysis of somatosensory induced oscillation (SIO) in RLS patients, that 93.3% of somatosensory induced Alpha (8-12 Hz) oscillations were successfully elicited, while 0% somatosensory induced Gamma (30-55 Hz) oscillations were elicited; which was significantly different from the control group. Additionally, in RLS patients exhibit increased excitability of the sensorimotor cortex, a remarkable abnormality existing in early somatosensory gating control (GC) and an attenuated inhibitory interneuron network, which consequently results in a compensatory mechanism through which RLS patients increase their attention-driven lower limb sensory gating control via somatosensory-induced Alpha (8-12 Hz) oscillation. This hyperexcitability, partially due to an electrocortical disinhibition, may have an important therapeutical implication, and become an important target of neuromodulatory interventions.

Functional Evaluation of Small Fiber Pathways in Primary Restless Legs Syndrome: Aδ Pathway Study

STUDY OBJECTIVES

The aim of this study was to provide a neurophysiological evaluation of the function of large and small fibers, particularly the peripheral part of the thermonociceptive Aδ pathway in patients with primary restless legs syndrome (RLS).

METHODS

The main evaluation was based on an analysis of the parameters of laser-evoked potentials (LEPs), N2 and P2 components, and an assessment of thermonociceptive thresholds (pain thresholds; PThs). Routine nerve conduction studies (NCS) were also performed.

RESULTS

No essential or important differences of clinical significance were observed in the parameters of large fiber conduction between the study and the control groups. Prolonged latencies of N2 and P2 potentials were obtained during foot stimulation in patients with primary RLS when compared to controls (N2, P2-lower right limb, and N2-lower left limb). We also observed higher amplitudes of LEPs evaluated as P2 and N2-P2 potentials in patients with primary RLS in comparison with the control group. Significantly higher (normal distribution P < .05) thermonociceptive thresholds in both lower and upper limbs were found in the RLS group.

CONCLUSIONS

On the basis of the analysis of LEPs and their comparison with the respective results from the control group, the presence of functional disability of the thermonociceptive Aδ pathway was confirmed in patients with primary RLS. The results indicated the presence of changes in the conduction of small fiber pathways in the pathomechanism of idiopathic RLS.