Changes in excitability of motor cortical circuitry in primary restless legs syndrome

Long latency trigemino-cervical reflex in restless legs syndrome

OBJECTIVE

The trigemino-cervical complex (TCC) seems under dopaminergic inhibitory control and the abnormalities of trigemino-cervical reflex (TCR) have been reported in disorders associated with the dopaminergic system and various pain disorders. If the inhibitory response in TCC is likely dopaminergic, we hypothesized that TCR, which has never been evaluated in restless legs syndrome (RLS) patients before, would be also abnormal.

METHODS

TCR was recorded from bilateral sternocleidomastoid and splenius capitis muscles in consecutive 15 drug-naive RLS patients and 16 age- and sex-matched healthy subjects. The right and left infraorbital branches of the trigeminal nerve were stimulated by percutaneous electrical stimulation separately. The presence rates, onset latencies, amplitudes, and durations of responses were measured and compared between patients with RLS and controls.

RESULTS

The presence rates, onset latencies and amplitudes of TCR responses were similar between RLS patients and controls, however, the durations of responses were bilaterally longer in RLS patients compared to healthy volunteers.

CONCLUSIONS

Hyperexcitability of TCR suggests defective sensory processing in the brainstem probably due to impairment of descending inhibitory dopaminergic system in RLS. The sensitization of TCC in RLS patients may also be a possible factor that might explain the association of RLS and pain disorders.

Involvement of central sensory pathways in subjects with restless legs syndrome: A neurophysiological study

In patients with restless legs syndrome (RLS) a motor cortical disinhibition has been reported in transcranial magnetic stimulation (TMS) studies, but the neuronal excitability in other cortical areas has been poorly explored. The aim of this study was the functional evaluation of thalamo-cortical circuits and inhibitory cortical responses in the sensory cortex in RLS. We assessed the high-frequency somatosensory evoked potentials (HF-SEP) in sixteen subjects suffering from RLS of different degrees of severity. In patients with severe or very severe RLS we found a significant desynchronization with amplitude reduction of both pre- and post-synaptic HF-SEP bursts, which suggest an impairment in the thalamo-cortical projections and in the cortical inhibitory interneurons activity, respectively. The assessment of the central sensory pathways by means of HF-SEP may shed light on the pathophysiological mechanisms of RLS.

Bidirectional association between irritable bowel syndrome and restless legs syndrome: a systematic review and meta-analysis

BACKGROUND

Several observational studies have shown that patients with irritable bowel syndrome (IBS) may have a high risk of restless legs syndrome (RLS). This systematic review and meta-analysis aimed to comprehensively investigate the bidirectional association between IBS and RLS.

METHODS

All conservational studies on IBS and RLS were searched in MEDLINE (assessed by PubMed), Embase, Web of Science, CINAHL, the Cochrane Library database and Google Scholar from inception to June 14, 2020. The Newcastle-Ottawa Scale and Agency for Healthcare Research and Quality were used to assess the methodological quality of the cohort and cross-sectional studies, respectively. The pooled odds ratio (OR) and 95% confidence interval (CI) were calculated using Reviewer Manager 5.3.

RESULT

A total of five cross-sectional studies of moderate methodological quality and one cohort study of high methodological quality were included in our review. Four cross-sectional studies and one cohort study involving 86 438 individuals met the criteria of IBS predicating the onset of RLS. Patients with IBS had a nearly three-fold increased odds of RLS compared with controls (OR = 2.60, 95%CI: 2.17-3.12, P < 0.00001; I² = 48%, P = 0.11). Three sensitivity analyses confirmed the robustness of the pooled result. Two cross-sectional studies involving 3581 individuals met the criteria of RLS predicating the onset of IBS. RLS patients had a nearly four-fold increased odds of IBS compared with controls without RLS (OR = 3.87, 95%CI: 1.73-8.66, P = 0.0010; I² = 77%, P = 0.04).

CONCLUSION

In this systematic review and meta-analysis, we found a substantial bidirectional association between IBS and RLS. More prospective, high-quality, population-based studies are warranted in the future.

Contribution of transcranial magnetic stimulation in restless legs syndrome: pathophysiological insights and therapeutical approaches

Transcranial magnetic stimulation (TMS) may offer a reliable means to characterize significant pathophysiologic and neurochemical aspects of restless legs syndrome (RLS). Namely, TMS has revealed specific patterns of changes in cortical excitability and plasticity, in particular dysfunctional inhibitory mechanisms and sensorimotor integration, which are thought to be part of the pathophysiological mechanisms of RLS rather than reflect a non-specific consequence of sleep architecture alteration. If delivered repetitively, TMS is able to transiently modulate the neural activity of the stimulated and connected areas. Some studies have begun to therapeutically use repetitive TMS (rTMS) to improve sensory and motor disturbances in RLS. High-frequency rTMS applied over the primary motor cortex or the supplementary motor cortex, as well as low-frequency rTMS over the primary somatosensory cortex, seem to have transient beneficial effects. However, further studies with larger patient samples, repeated sessions, an optimized rTMS setup, and clinical follow-up are needed in order to corroborate preliminary results. Thus, we performed a systematic search of all the studies that have used TMS and rTMS techniques in patients with RLS.

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.

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.

Clinical and electrophysiological impact of repetitive low-frequency transcranial magnetic stimulation on the sensory-motor network in patients with restless legs syndrome

Background

Based on the hyperexcitability and disinhibition observed in patients with restless legs syndrome (RLS) following transcranial magnetic stimulation (TMS), we conducted a study with low-frequency repetitive TMS (rTMS) over the primary motor (M1) and somatosensory cortical areas (S1) in patients with RLS.

Methods

A total of 13 right-handed patients and 10 age-matched controls were studied using clinical scales and TMS. Measurements included resting motor threshold (rMT), motor-evoked potentials (MEPs), cortical silent period (CSP), and central motor conduction time (CMCT). A single evening session of rTMS (1 Hz, 20 trains, 50 stimuli each) was administered over the left M1, left S1, and sham stimulation over M1 in a random order. Clinical and TMS measures were repeated after each stimulation modality.

Results

Baseline CSP was shorter in patients than in controls and remained shorter in patients for both motor and somatosensory stimulation. The patients reported a subjective improvement of both initiating and maintaining sleep the night after the rTMS over S1. Patients exhibited a decrease in rMT after rTMS of S1 only, although the effect was smaller than in controls. MEP latency and CMCT changed only in controls after stimulation. Sham stimulation was without effect on the observed variables.

Conclusions

rTMS on S1-M1 connectivity alleviated the sensory-motor complaints of RLS patients. The TMS indexes of excitation and inhibition indicate an intracortical and corticospinal imbalance, mainly involving gamma-aminobutyric acid (GABA)ergic and glutamatergic circuitries, as well as an impairment of the short-term mechanisms of cortical plasticity. The rTMS-induced activation of the dorsal striatum with the consequent increase of dopamine release may have contributed to the clinical and neurophysiological outcome.

Clinical and electrophysiological impact of repetitive low-frequency transcranial magnetic stimulation on the sensory-motor network in patients with restless legs syndrome

BACKGROUND

Based on the hyperexcitability and disinhibition observed in patients with restless legs syndrome (RLS) following transcranial magnetic stimulation (TMS), we conducted a study with low-frequency repetitive TMS (rTMS) over the primary motor (M1) and somatosensory cortical areas (S1) in patients with RLS.

METHODS

A total of 13 right-handed patients and 10 age-matched controls were studied using clinical scales and TMS. Measurements included resting motor threshold (rMT), motor-evoked potentials (MEPs), cortical silent period (CSP), and central motor conduction time (CMCT). A single evening session of rTMS (1 Hz, 20 trains, 50 stimuli each) was administered over the left M1, left S1, and sham stimulation over M1 in a random order. Clinical and TMS measures were repeated after each stimulation modality.

RESULTS

Baseline CSP was shorter in patients than in controls and remained shorter in patients for both motor and somatosensory stimulation. The patients reported a subjective improvement of both initiating and maintaining sleep the night after the rTMS over S1. Patients exhibited a decrease in rMT after rTMS of S1 only, although the effect was smaller than in controls. MEP latency and CMCT changed only in controls after stimulation. Sham stimulation was without effect on the observed variables.

CONCLUSIONS

rTMS on S1-M1 connectivity alleviated the sensory-motor complaints of RLS patients. The TMS indexes of excitation and inhibition indicate an intracortical and corticospinal imbalance, mainly involving gamma-aminobutyric acid (GABA)ergic and glutamatergic circuitries, as well as an impairment of the short-term mechanisms of cortical plasticity. The rTMS-induced activation of the dorsal striatum with the consequent increase of dopamine release may have contributed to the clinical and neurophysiological outcome.

The duration of the cortical silent period is not abnormal in Restless Legs Syndrome/Willis-Ekbom Disease

OBJECTIVE

To compare the duration of the cortical silent period (CSP) measured in a hand muscle in subjects with primary Restless Legs Syndrome (RLS/WED) and controls, using four different methods of analysis.

METHODS

The CSP to transcranial magnetic stimulation of the dominant motor cortex was assessed in the abductor digiti minimi of 33 subjects with RLS/WED and 24 controls. CSP duration was measured by an automated and three visually-guided methods.

RESULTS

There were significant differences between absolute values of CSP duration according to the method of analysis. However, irrespectively of the method used for CSP assessment, no differences were found between measurements performed in subjects with RLS/WED and subjects from the control group.

CONCLUSIONS

Absolute values of CSP durations analyzed by different methods should not be directly compared, because significantly different results can be obtained from the same data set.

SIGNIFICANCE

The CSP assessed from a hand muscle is unlikely to be a biomarker of primary RLS/WED. Our results highlight the importance of standardizing the definition of CSP onset and offset, as well as of describing in detail the methodology chosen to record and measure CSP duration, in order to enable comparisons between studies.

F-Wave Duration as a Specific and Sensitive Tool for the Diagnosis of Restless Legs Syndrome/Willis-Ekbom Disease

STUDY OBJECTIVES

Restless legs syndrome, also known as Willis-Ekbom disease (RLS/WED), is a frequent condition, though its pathophysiology is not completely understood. The diagnosis of RLS/WED relies on clinical criteria, and the only instrumental tool, the suggested immobilization test, may lead to equivocal results. Recently, neurophysiological parameters related to F-wave duration have been proposed as a diagnostic aid. The aim of this study is to assess and compare the diagnostic values of these parameters in diagnosis of RLS/WED.

METHODS

Fifteen women affected by primary RLS/WED and 17 age- and sex- matched healthy subjects. A complete electroneurographic evaluation, including nerve conduction studies (NCS), cutaneous silent period (CSP), and F-wave parameters, namely amplitude, F-wave duration (FWD), and the ratio between FWD and duration of the corresponding compound muscle action potential (FWD/CMAPD).

RESULTS

No subject showed alterations of the NCS. However, FWD and FWD/CMAPD of both upper and lower limbs were significantly longer in patients than controls. Tibial FWD/CMAPD best discriminated RLS/WED patients from controls. A cutoff of 2.06 yielded a sensitivity of 69.2%, a specificity of 94.1%, a positive predictive power of 90%, and a negative predictive power of 80% (area under the curve = 0.817; 95% confidence interval = 0.674-0.959). The combination of ulnar or tibial FWD/CMAPD increases the sensitivity (85.7%) while slightly decreasing the specificity (87.5%, positive predictive value: 85.7%, negative predictive value: 87.5%).

CONCLUSIONS

Lower limb FWD/CMAPD ratio may represent a supportive diagnostic tool, especially in cases of evening lower leg discomfort of unclear interpretation.

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.

Repetitive Transcranial Magnetic Stimulation for the Treatment of Restless Legs Syndrome

Background:

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive technique used to alter cortex excitability that has been proposed as an efficient method for treating brain hyperexcitability or hypoexcitability disorders. The aim of this study was to investigate whether high-frequency rTMS could have any beneficial effects in restless legs syndrome (RLS).

Methods:

Fourteen patients with RLS were given high-frequency rTMS (15 Hz, 100% motor threshold) to the leg representation motor cortex area of the frontal lobe for 14 sessions over 18 days. Patients were diagnosed according to the international criteria proposed by the International Restless Legs Syndrome Study Group in 2003. The International RLS Rating Scale (IRLS-RS), Pittsburgh Sleep Quality Index (PSQI), Hamilton Anxiety Scale (HAMA) and Hamilton Depression Scale were used to evaluate the severity of RLS, sleep quality, anxiety and depression, respectively. The scale scores were evaluated at four-time points (baseline, end of the 14^th session, and at 1- and 2-month posttreatment). One-way analysis of variance was used to compare scale scores at different time points.

Results:

There was significant improvement in the IRLS-RS (from 23.86 ± 5.88 to 11.21 ± 7.23, P < 0.05), PSQI (from 15.00 ± 4.88 to 9.29 ± 3.91, P < 0.05), and HAMA (from 17.93 ± 7.11 to 10.36 ± 7.13, P < 0.05) scale scores at the end of 14^th session, with ongoing effects lasting for at least 2 months.

Conclusions:

High-frequency rTMS can markedly alleviate the motor system symptoms, sleep disturbances, and anxiety in RLS patients. These results suggest that rTMS might be an option for treating RLS.

Transcranial magnetic stimulation for evaluation of motor cortical excitability in restless legs syndrome/Willis-Ekbom disease

There is no consensus about mechanisms underlying restless legs syndrome (RLS), also known as Willis-Ekbom disease (WED). Cortical excitability may be abnormal in RLS. Transcranial magnetic stimulation (TMS) can provide insight about cortical excitability. We reviewed studies about measures of excitability to TMS in RLS. Original studies published between January 1999 and January 2015 were searched in PubMed, Scopus, and Web of Science databases. Inclusion criteria were as follows: original studies involving primary RLS in patients from both sexes and ages between 18 and 85 years; TMS protocols clearly described; and they were written in English, in peer-reviewed journals. Fifteen manuscripts were identified. TMS protocols were heterogeneous across studies. Resting motor threshold, active motor threshold, and amplitudes of motor-evoked potentials were typically reported to be normal in RLS. A reduction in short-interval intracortical inhibition (SICI) was the most consistent finding, whereas conflicting results were described in regard to short-interval intracortical facilitation and the contralateral silent period. Decreased SICI can be reversed by treatment with dopaminergic agonists. Plasticity in the motor cortex and sensorimotor integration may be disrupted. TMS may become a useful biomarker of responsiveness to drug treatment in RLS. The field can benefit from increases in homogeneity and sizes of samples, as well as from decrease in methodological variability across studies.

Distinctive patterns of cortical excitability to transcranial magnetic stimulation in obstructive sleep apnea syndrome, restless legs syndrome, insomnia, and sleep deprivation

Altered responses to transcranial magnetic stimulation (TMS) in obstructive sleep apnea syndrome (OSAS), restless legs syndrome (RLS), insomnia, and sleep-deprived healthy subjects have been reported. We have reviewed the relevant literature in order to identify eventual distinctive electrocortical profiles based on single and paired-pulse TMS, sensorimotor modulation, plasticity-related and repetitive TMS measures. Although obtained from heterogeneous studies, the detected changes might be the result of the different pathophysiological substrates underlying OSAS, RLS, insomnia and sleep deprivation rather than reflect the general effect of non-specific sleep loss and instability. OSAS tends to exhibit an increased motor cortex inhibition, which is reduced in RLS; intracortical excitability seems to be in favor of an "activating" profile in chronic insomnia and in sleep-deprived healthy individuals. Abnormal plasticity-related TMS phenomena have been demonstrated in OSAS and RLS. This review provides a perspective of TMS techniques by further understanding the role of neurotransmission pathways and plastic remodeling of neuronal networks involved in common sleep disorders. TMS might be considered a valuable tool in the assessment of sleep disorders, the evaluation of the effect of therapy and the design of non-pharmacological approaches.

Direct comparison of cortical excitability to transcranial magnetic stimulation in obstructive sleep apnea syndrome and restless legs syndrome

OBJECTIVE

Changes to transcranial magnetic stimulation (TMS) have been reported in obstructive sleep apnea syndrome (OSAS) and restless legs syndrome (RLS), although no direct comparison study is available. The aim of this new investigation is to assess and compare cortical excitability of OSAS and RLS patients using the same methodology and under the same experimental conditions.

METHODS

Fourteen patients with OSAS and 12 with RLS were compared to 14 age-matched controls. All patients were untreated and had a severe degree of disease. Resting motor threshold (rMT), cortical silent period (CSP) and motor evoked potentials MEPs, as well as intracortical inhibition (ICI) and facilitation at interstimulus interval (ISI) of 3 and 10 ms, respectively, were explored from the right first dorsal interosseous muscle, during wakefulness.

RESULTS

rMT was higher in OSAS than in RLS and controls. CSP was shorter in RLS only when compared to apneic patients, whereas it was similar between OSAS and controls. OSAS subjects exhibited slightly prolonged central motor conductivity, whereas MEP amplitude was smaller in both patient groups. The ICI ratio at ISI of 3 ms was decreased in RLS patients only.

CONCLUSIONS

Distinct changes of responses at TMS were found, probably connected with the different neurophysiological substrates underlying OSAS and RLS and could not be interpreted as a mere reflection of the effects of sleep architecture alteration. TMS can be considered an additional tool for the understanding of clinical and pathophysiological aspects of sleep disorders, and possibly for the evaluation of the effect of therapy.

Pharmacological treatment of sleep disorders and its relationship with neuroplasticity

Sleep and wakefulness are regulated by complex brain circuits located in the brain stem, thalamus, subthalamus, hypothalamus, basal forebrain, and cerebral cortex. Wakefulness and NREM and REM sleep are modulated by the interactions between neurotransmitters that promote arousal and neurotransmitters that promote sleep. Various lines of evidence suggest that sleep disorders may negatively affect neuronal plasticity and cognitive function. Pharmacological treatments may alleviate these effects but may also have adverse side effects by themselves. This chapter discusses the relationship between sleep disorders, pharmacological treatments, and brain plasticity, including the treatment of insomnia, hypersomnias such as narcolepsy, restless legs syndrome (RLS), obstructive sleep apnea (OSA), and parasomnias.

Transcranial magnetic stimulation and sleep disorders: pathophysiologic insights

The neural mechanisms underlying the development of the most common intrinsic sleep disorders are not completely known. Therefore, there is a great need for noninvasive tools which can be used to better understand the pathophysiology of these diseases. Transcranial magnetic stimulation (TMS) offers a method to noninvasively investigate the functional integrity of the motor cortex and its corticospinal projections in neurologic and psychiatric diseases. To date, TMS studies have revealed cortical and corticospinal dysfunction in several sleep disorders, with cortical hyperexcitability being a characteristic feature in some disorders (i.e., the restless legs syndrome) and cortical hypoexcitability being a well-established finding in others (i.e., obstructive sleep apnea syndrome narcolepsy). Several research groups also have applied TMS to evaluate the effects of pharmacologic agents, such as dopaminergic agent or wake-promoting substances. Our review will focus on the mechanisms underlying the generation of abnormal TMS measures in the different types of sleep disorders, the contribution of TMS in enhancing the understanding of their pathophysiology, and the potential diagnostic utility of TMS techniques. We also briefly discussed the possible future implications for improving therapeutic approaches.

Disrupted central inhibition after transcranial magnetic stimulation of motor cortex in schizophrenia with long-term antipsychotic treatment

Aims. Schizophrenia is a neuropsychiatric disorder associated with mental and motor disturbances. We aimed to investigate motor control, especially central silent period (CSP) in subjects with schizophrenia (n = 11) on long-term antipsychotic treatment compared to healthy controls (n = 9). Methods. Latency and duration of motor evoked potentials (MEPs) and CSPs were measured with the help of single pulse transcranial magnetic stimulation (TMS) and intramuscular electrodes. After stimulation of the dominant and nondominant motor cortex of abductor digiti minimi (ADM) and tibialis anterior (TA) muscle areas, respective responses were measured on the contralateral side. Results. MEPs did not differ significantly between the groups. Multiple CSPs were found predominantly in subjects with schizophrenia, which showed a higher number of CSPs in the dominant ADM and the longest summarized duration of CSPs in the nondominant ADM (P < 0.05) compared to controls. Conclusions. There were multiple CSPs predominantly in the upper extremities and in the dominant body side in subjects with schizophrenia. Behind multiple CSPs may lie an impaired regulation of excitatory or inhibitory neurotransmitter systems in central motor pathways. Further research is needed to clarify the role of the intramuscular recording methods and the effect of antipsychotics on the results.

Recurrent CSPs after Transcranial Magnetic Stimulation of Motor Cortex in Restless Legs Syndrome

Aims. The aim of this study was to investigate the motor control and central silent period (CSP) in restless legs syndrome (RLS). Methods. Transcranial magnetic stimulation was focused on the dominant and nondominant hemispheric areas of motor cortex in six subjects with RLS and six controls. The responses were recorded on the contralateral abductor digiti minimi (ADM) and tibialis anterior (TA) muscles with intramuscular needle electrodes. Results. No significant differences were found in the motor conduction or central motor conduction time, in the latency, or in the duration of the CSPs between or within the groups, but multiple CSPs were observed in both groups. The number of the CSPs was significantly higher in both ADMs and in the dominant TA (P ≤ 0.01) in the RLS group compared to the controls. Conclusion. Descending motor pathways functioned correctly in both groups. The occurrence of the recurrent CSPs predominantly in the RLS group could be a sign of a change of function in the inhibitory control system. Further research is needed to clarify the role of the intramuscular recording technique and especially the role of the subcortical generators in the feedback regulation of the central nervous system in RLS.

Cırcadian changes in cortical excitability in restless legs syndrome

Various investigations have revealed a widespread and somewhat controversial pattern of cerebral, cerebellar and brainstem involvement in the pathophysiology of restless legs syndrome (RLS). However, several studies which investigated functional or structural aspects indicated cortical involvement in RLS. In this study, we aimed to analyze circadian changes of cortical excitability in idiopathic RLS patients by means of transcranial magnetic stimulation (TMS). Eleven idiopathic RLS patients and eight healthy age and sex matched subjects were investigated using single-pulse TMS and motor nerve conduction studies during early afternoon when there were no symptoms and late at night (22:00-23:00) when the symptoms reappeared. Central motor conduction time, latencies and amplitudes of scalp and cervical motor evoked potentials, resting and active motor thresholds, and cortical silent period were measured. Measured parameters were similar between RLS patients and healthy subjects during the daytime. At night, cortical silent periods tended to shorten, and motor thresholds tended to decrease in the RLS group, whereas in controls they tended to increase. At night, active motor-threshold measurements were significantly lower in the RLS group (28.5 ± 6.2% vs 40.4 ± 8.4%, p=0.006). Therefore, we propose that in patients with RLS, conduction along the motor corticospinal axons is normal, with the possible loss of subcortical inhibition at nighttime.

Changes of cortical excitability after dopaminergic treatment in restless legs syndrome

OBJECTIVE

Dopaminergic pathways are most likely involved in the pathophysiology of restless legs syndrome (RLS). In previous investigations, an alteration of cortical excitability was suggested to be related to a dopaminergic dysfunction in RLS. The purpose of our study was to compare practice-dependent plasticity in RLS patients before and after a month of dopaminergic treatment.

METHODS

Single-pulse transcranial magnetic stimulation (TMS) was used to define motor evoked potential (MEP) amplitude, motor threshold, and silent period (SP) as well. Subjects performed three exercise blocks (bimanual motor task). MEP amplitude, registered immediately after each exercise block and after a rest period, was compared to baseline. The time course of intra-cortical inhibition was tested using paired-pulse TMS at short inter-stimulus intervals. For the single-pulse TMS procedures, we enrolled 12 patients affected by primary RLS and 12 normal subjects. For the paired-pulse TMS procedures, only six patients underwent the examination. RLS patients underwent the examination in both pre- and post-dopaminergic treatment conditions.

RESULTS

In RLS patients MEP amplitude increased after the rest period only in the post-treatment condition, showing a delayed facilitation. After exercise, MEP amplitude increased, but not enough to be significant, showing a positive trend but not a clear-cut post-exercise facilitation. In the pre-treatment condition instead, MEP amplitude did not change either after rest period or after exercise. RLS patients showed a marked increase of the central motor inhibition, assessed by using paired-pulse TMS at short inter-stimulus intervals after pramipexole treatment. On the contrary, the duration of the SP did not change compared to the pre-treatment condition.

CONCLUSIONS

In RLS patients after dopaminergic treatment, the main finding was the changing of MEP amplitude after rest following a motor task. Since dopaminergic treatment can reverse delayed facilitation in RLS, we hypothesized that cortical plasticity related to dopaminergic systems may play a crucial role in RLS pathophysiology.

Scopoli's work in the field of mercurialism in light of today's knowledge: past and present perspectives

The Idrija Mercury Mine (1490-1994) appointed its first physician, Joannes Antonius Scopoli, in 1754. Most of his descriptions of mercurialism are still relevant today. This study highlights Scopoli's observations on the interaction between elemental mercury (Hg degrees ) and alcohol, on the appearance of lung impairment, insomnia, and depressive mood in mercurialism. This presentation is based on Scopoli's experiences presented in his book, De Hydrargyro Idriensi Tentamina (1761), current knowledge, and our own experience acquired through health monitoring of occupational Hg degrees exposure. Some studies have confirmed Scopoli's observation that alcohol enhances mercurialism and his hypothesis that exposure to high Hg degrees concentrations causes serious lung impairment. Neurobiological studies have highlighted the influence of Hg degrees on sleep disorder and depressive mood observed by Scopoli. Although today's knowledge provides new perspectives of Scopoli's work on mercurialism, his work is still very important and can be considered a part of occupational medicine heritage.

[Pathophysiology of restless legs syndrome]

Restless legs syndrome (RLS) could be the consequence of sensorimotor dysfunction. Dopaminergic treatment has been successful in RLS, suggesting dopaminergic abnormalities. The specific pathophysiology of idiopathic RLS is not well known but recent studies have raised the hypothesis of diencephalospinal pathway dysfunction. This pathway includes spinal, subcortical and cortical structures. In idiopathic RLS, an implication of A11 neurons has been evoked, but further studies are needed to confirm this hypothesis. Brain iron is reduced in RLS. This decrease plays a major role in RLS occurrence. Genetic analyses are necessary to better understand the pathophysiological mechanisms of RLS.

In restless legs syndrome, the neural substrates of the sensorimotor symptoms are also normally involved in upright standing posture and biped walking

Restless legs syndrome (RLS) exhibits sensorimotor symptoms. In familial cases, a gene at chromosomal location 9p-24-22 is linked to RLS and the expressed mutation is Dopamine Receptor Specific Individual Sensitivity (DRSIS). The symptoms are triggered during changes in alertness, generally at sleep hours, resulting from insufficient dopamine transmission. The conscious experience of sensory abnormalities are described as 'an urge to move the limbs with or without paresthesias' leading to motor signs such as periodic limb movements and motor restlessness which exhibit temporary loss of extensor motor system dominance over the flexor motor system of the upright posture. The relationship of the expressed mutation to EEG alpha activity makes RLS a sleep disorder as well as a cognitive dysfunction. The recurrent character of sensorimotor symptoms impede the patient's ability to sleep, wake and force to move leading to insomnia. In Uner Tan Syndrome, the nonsense mutation in the same gene leads to underdevelopment of the neural substrates of upright posture. The defects include dopamine receptor deficiency (DRD) leading to severe cognitive dysfunctions and motor disorders-complete loss of extensor motor system dominance over the flexor motor system-quadrupedality, primitive speech, cerebellar symptoms, and strabismus. Comparisons between the neural substrates of sensorimotor symptoms seen in RLS and MRI findings for cases of Uner Tan Syndrome show cortico-cerebellar hypoplasias in the neural networks involved in upright posture. Both RLS and Uner Tan Syndrome seem to be due to different mutations in the dopamine receptor gene at 9p-24 locus, affecting the diencephalon dopaminergic system and the neural networks involved in upright posture.

Restless legs syndrome: pathophysiology, diagnosis and treatment

Restless legs syndrome (RLS) is clinically defined by the presence of (i) an urge to move the legs with or without an actual paraesthesia; (ii) a worsening of symptoms with inactivity; (iii) improvement with activity; and (iv) a worsening of symptoms in the evening and at night. Patients may use a variety of semantic phrases to describe their symptoms but all must have an urge to move. Most people with RLS also have periodic limb movements during sleep, although this is not part of the clinical diagnostic criteria. RLS is very common. About 10% of all Caucasian populations have RLS, although it may be mild in the majority of cases. Women generally outnumber men by about 2:1. As a general rule, RLS severity worsens through the first seven to eight decades of life, but may actually lessen in old age. The aetiology of RLS is only partly understood. There is a strong genetic component, and several genetic linkages and three causative genes have been identified worldwide. Several medical conditions, including renal failure, systemic iron deficiency and pregnancy, and possibly neuropathy, essential tremor and some genetic ataxias, are also associated with high rates of RLS. In all cases to date, the actual CNS pathology of RLS demonstrates reduced iron stores, in a pattern that suggests that the homeostatic control of iron is altered, not just that there is not enough iron entering the brain. The relationship between reduced CNS iron levels and the clinical phenotype or treatment response to dopaminergics is not known but generates promising speculation. Treatment of RLS is usually rewarding. Most patients respond robustly to dopamine receptor agonists. Over time, response may lessen, or the patients may develop 'augmentation', whereby they have a worsening of symptoms, usually in the form of an earlier onset. Other treatment options include gabapentin, or similar antiepileptic drugs, and opioids. High-dose intravenous iron is a promising but still experimental approach.

Influence of cabergoline on motor excitability in patients with restless legs syndrome

To investigate whether the increased urge to move the legs in restless legs syndrome (RLS) corresponds to an electrophysiological phenomenon and whether motor excitability or behavior is influenced by the treatment with a dopamine agonist. We examined 10 patients who had RLS with transcranial magnetic stimulation (TMS) before and during treatment with the dopamine agonist cabergoline. Results were compared with data obtained from healthy subjects. Inhibitory mechanisms were explored by measurement of the cortical silent period (cSP). Recordings were obtained from the right anterior tibial muscle. Clinical severity of RLS was rated using the International Restless Legs Syndrome Study Group Rating Scale (IRLSSGRS). During therapy with cabergoline, all patients reported a significant improvement of RLS symptoms. Before medication, patients showed a significant shortening of cSP compared with healthy subjects. After 14 days of treatment with cabergoline, cSP normalized in RLS patients; 90 days after the start of daily cabergoline, cSP tended to shorten again, whereas RLS symptoms further improved. There was no correlation between cSP duration and IRLSSGRS results. There were no differences in patient and control motor thresholds. These thresholds remained unchanged during treatment with cabergoline. RLS patients have a disturbance of inhibitory neurons that can temporarily be reversed with a dopamine agonist. However, the cSP does not correlate with the clinical symptoms.

Cutaneous silent period in patients with restless leg syndrome

OBJECTIVE

To investigate the pathophysiological relationship between RLS and small fiber neuropathy using the cutaneous silent period (CSP), which is a spinal reflex mediated by Adelta cutaneous afferents and is useful for the evaluation of small-diameter nerve function.

METHODS

The CSP was measured from the extensor digitorum brevis in 157 patients with RLS and 60 healthy controls. The CSP measurement was repeated in the RLS patients after dopamine agonist treatment for one month. The RLS rating scale for clinical severity was used to evaluate each patient before and after treatment. The measured CSP variables were compared between the patient group and the control group. In addition, the possible correlation between the CSP variables and the RLS rating scale score related to treatment was analyzed.

RESULTS

The mean CSP latencies did not differ between the RLS patients and the healthy controls; however, the mean CSP duration was significantly longer in the RLS patients than in the controls, and this prolonged CSP duration improved to the level of the control subjects after dopamine agonist treatment (p=0.003). The mean RLS rating scale score also significantly decreased after medication (p=0.000). However, the changes in the CSP variables did not correlate with the decrement in the RLS rating scale score.

CONCLUSIONS

Although our results do not support the role of Adelta fiber dysfunction in RLS, the observed change in CSP duration may be useful as a clinical measure of the improvement with dopamine agonist treatment in patients with RLS.

SIGNIFICANCE

Further study is needed to elucidate the exact mechanism involved in the prolonged CSP duration in response to treatment.

In restless legs syndrome, during changes in vigilance, the forced EEG shifts from alpha activity to delta or high alpha may lead to the altered states of dopamine receptor function and the symptoms

RLS cases may carry a genetic vulnerability called EEG alpha activity gate dyscontrols which appear during changes in vigilance and generally during sleep. It is triggered by forced EEG shifts either from alpha activity to delta or high alpha. Expressions of alpha activity gate dyscontrols may have a gate effect that trigger a second vulnerability-dopamine receptor specific individual sensitivity (DRSIS) and this leads to a deficiency in dopamine transmissions at diencephalospinal dopamine system (DSDS). Due to altered gene expressions in states of dopamine receptor function, DRSIS EEGs and RLS symptoms may be interpreted as follows: A. Disinhibition state is alpha activity gate dyscontrols induced inhibition of DSDS inhibitory dopamine modulations. Dopaminergic disinhibitions inhibit inhibitory interneurons of sensory and motor nuclei neurons that are involved in RLS. These sleep sensitive inhibitory interneurons possibly have GABA-ergic functions in sleep. (I) DSDS thalamic neurons' disinhibitory effects in thalamus on GABA-ergic interneurons of: (a) Intralaminar nuclei non-discriminative sensation neurons at thalamocortical premotor network leading to symptom of "a sense of urgency to move" generally referenced to legs.(b) Reticular thalamic nucleus (RTN) neurons. At polysomnography,during NREM sleep, disinhibited RTN neurons show alpha activity gate dyscontrol 1. These are recurrent subtypes of CAP in alpha band (7-12 Hz) pointing a difficulty in shifting to subtypes of CAP in low delta bands (0.25-2.5 Hz) and sleep fragmentations.(II) Supraspinal disinhibitory projections from DSDS thalamic neurons on GABA-ergic interneurons of: (a) Sensory neurons at posterior horns of spinal cord leading to dysesthesias, generally referenced to legs.(b) Medullary-reticulospinal neurons and by way of independent spinal rhythm generators on motoneurons leading to periodic limb movements in sleep.B. Activation state is an increase in symptoms. Sensory intralaminar and motor pontin nuclei neurons are in fact excitatory but are disinhibited in RLS. Due to altered gene expression, these neurons begin to perceive 'disinhibition' as reduced inhibition. Their glutamate receptors may activate deficient dopamine transmissions on RTN leading to alpha activity gate dyscontrol 2. This implies a failure in preventing shifts to frequent subtypes of CAP in high alpha and low beta bands (12-13 Hz) resulting in an increase of sensorimotor symptoms and appearance of motor restlessness, behavioral arousals and insomnia. C. Inhibition state is spontaneous relief from sensorimotor symptoms. Short or long-term synaptic plasticities of dopamine receptors towards activations initiate negative feedbacks from inhibitory interneurons. They are supported by inhibitory dopamine modulations- alertness and some awareness generally with regular high alpha EEGs, supraspinal inhibitions and a reverse movement pattern of PLMS during standing up and continuing to walk.

Disorders of pulmonary function, sleep, and the upper airway in Charcot-Marie-Tooth disease

Charcot-Marie Tooth disease (CMT) encompasses several inherited peripheral motor-sensory neuropathies and is one of the most common inherited neuromuscular diseases. Charcot-Marie-Tooth disease can be associated with several disorders that may be encountered by the pulmonary physician, including restrictive pulmonary impairment, sleep apnea, restless legs, and vocal cord dysfunction. Restrictive pulmonary impairment has been described in association with phrenic nerve dysfunction, diaphragm dysfunction, or thoracic cage abnormalities. Central sleep apnea may be associated with diaphragm dysfunction and hypercapnia, whereas obstructive sleep apnea has been reported as possibly due to a pharyngeal neuropathy. Restless legs and periodic limb movement during sleep are found in a large proportion of patients with CMT2, a type of CMT associated with prominent axonal atrophy. Vocal cord dysfunction, possibly due to laryngeal nerve involvement, is found in association with several CMT types and can often mimic asthma. There may be special therapeutic considerations for the treatment of those conditions in individuals with CMT. For instance, bi-level positive airway pressure may be more appropriate than continuous positive airway pressure (CPAP) for the treatment of sleep apnea in the individual with concomitant restrictive pulmonary impairment. The prominence of peripheral neuropathy as a cause of the restless legs syndrome in CMT may justify treatment with neuropathic medications as opposed to the more commonly recommended dopaminergic agents. The risk of progression to bilateral vocal cord dysfunction in CMT and the risk of aspiration with laryngeal neuropathy may limit the therapeutic options available for vocal cord paralysis.

Animal studies in restless legs syndrome

Although restless legs syndrome (RLS) is a common disorder that has been studied thoroughly in the past decades, the underlying pathophysiology is still not fully understood. However, some attractive hypotheses on the pathogenesis of the disorder have been forwarded. Animal models are an important tool to verify hypotheses and to dissect out the details of pathophysiological mechanisms. Ideally they might serve the development of future treatment strategies. This review discusses the general and specific prerequisites necessary for the establishment of animal models for RLS and summarizes the approaches that have been made.

Possible joint origin of restless leg syndrome (RLS) and migraine

Sleep disorders have been described in migraine patients. Among sleep disorders RLS has been reported in up to one-third of migraineurs. Adverse effects of anti migraine therapy by dopamine antagonists can not fully explain this association. Therefore we present the hypothesis that RLS and migraine may have a joint origin. The hypothesis is supported by: (1) the same genetic origin for migraine without aura and RLS in single Italian family on chromosome 14q21; this gene codes survival motor neuron-interacting protein 1 (SIP1) which can play role in both diseases. (2) Correlation of both RLS and migraine with fibromyalgia. (3) Alteration of cortical excitability in both migraine and RLS.

Cabergoline reverses cortical hyperexcitability in patients with restless legs syndrome

OBJECTIVE

To reverse the profile of abnormal intracortical excitability in patients with restless legs syndrome (RLS) by administering the dopaminergic agonist cabergoline.

METHODS

The effects of this drug on motor cortex excitability were examined with a range of transcranial magnetic stimulation (TMS) protocols before and after administration of cabergoline over a period of 4 weeks in 14 patients with RLS and in 15 healthy volunteers. Measures of cortical excitability included central motor conduction time; resting and active motor threshold to TMS; duration of the cortical silent period; short latency intracortical inhibition (SICI) and intracortical facilitation using a paired-pulse TMS technique.

RESULTS

Short latency intracortical inhibition was significantly reduced in RLS patients compared with the controls and this abnormal profile was reversed by treatment with cabergoline; the other TMS parameters did not differ significantly from the controls and remained unaffected after treatment with cabergoline. Cabergoline had no effect on cortical excitability of the normal subjects.

CONCLUSIONS

As dopaminergic drugs are known to increase SICI, our findings suggest that RLS may be caused by a central nervous system dopaminergic dysfunction. This study demonstrates that the cortical hyperexcitability of RLS is reversed by cabergoline, and provides physiological evidence that this dopamine agonist may be a potentially efficacious option for the treatment of RLS.

Restless legs syndrome

Is treatable but under-recognised

Restless legs syndrome: a review

Restless legs syndrome (RLS) is a sensorimotor disorder characterized by an irresistible urge to move the limbs accompanied by uncomfortable sensations, leading to sleep disturbances. It is associated with psychiatric comorbidities and a decreased quality of life. RLS is common and most severe among females and the elderly. It may be primary or secondary to other conditions and may be familial. Linkage to several chromosomal loci have been demonstrated. The pathogenesis of RLS involves dopaminergic dysfunction, iron metabolism, and abnormalities in supraspinal inhibition. The mainstay of RLS therapy are dopamine agonists or levodopa. This article reviews the clinical characteristics, epidemiology, diagnosis, pathogenesis, and treatment of RLS.