A patient-enriched MEIS1 coding variant causes a restless legs syndrome-like phenotype in mice

Restless legs syndrome (RLS) is a neurological disorder characterized by uncomfortable or unpleasant sensations in the legs during rest periods. To relieve these sensations, patients move their legs, causing sleep disruption. While the pathogenesis of RLS has yet to be resolved, there is a strong genetic association with the MEIS1 gene. A missense variant in MEIS1 is enriched sevenfold in people with RLS compared to non-affected individuals. We generated a mouse line carrying this mutation (p.Arg272His/c.815G>A), referred to herein as Meis1R272H/R272H (Meis1 point mutation), to determine whether it would phenotypically resemble RLS. As women are more prone to RLS, driven partly by an increased risk of developing RLS during pregnancy, we focused on female homozygous mice. We evaluated RLS-related outcomes, particularly sensorimotor behavior and sleep, in young and aged mice. Compared to noncarrier littermates, homozygous mice displayed very few differences. Significant hyperactivity occurred before the lights-on (rest) period in aged female mice, reflecting the age-dependent incidence of RLS. Sensory experiments involving tactile feedback (rotarod, wheel running, and hotplate) were only marginally different. Overall, RLS-like phenomena were not recapitulated except for the increased wake activity prior to rest. This is likely due to the focus on young mice. Nevertheless, the Meis1R272H mouse line is a potentially useful RLS model, carrying a clinically relevant variant and showing an age-dependent phenotype.

Potential therapeutic benefit of spinal cord stimulation in restless legs syndrome: scoping review and mechanistic considerations

BACKGROUND

Restless legs syndrome (RLS) is a prevalent sensorimotor disorder that can dramatically impair sleep quality, daytime function, and quality of life. Although many patients benefit from standard pharmacological therapy, some patients suffer from insufficient treatment response or medication intolerance. Novel treatment approaches are therefore necessary.

OBJECTIVE

Given the overlap between RLS and pain syndromes in both pathophysiological mechanisms and certain treatment options, we aimed to perform a scoping review of the available evidence on spinal cord stimulation (SCS) for RLS and discuss potential mechanistic implications.

METHODS

We identified a total of 16 cases of patients with RLS who underwent SCS, all from case reports or case series.

DISCUSSION

The published evidence is insufficient to assess SCS efficacy in patients with RLS, but SCS remains a promising investigational therapy in RLS on the basis of its potential mitigatory effects in the central hyperexcitability of the sensorimotor cortex through neuromodulation of spinal, subcortical, and cortical areas. A call for further research in this field is presented, with suggestions for future directions and trial designs.

Defect of the Endogenous Inhibitory Pain System in Idiopathic Restless Legs Syndrome: A Laser Evoked Potentials Study

BACKGROUND

Restless legs syndrome (RLS) is a complex sensorimotor disorder. Symptoms worsen toward evening and at rest and are temporarily relieved by movement. Symptoms are perceived as painful in up to 45% of cases, and nociception system may be involved.

OBJECTIVES

To assess the descending diffuse noxious inhibitory control in RLS patients.

METHODS

Twenty-one RLS patients and twenty age and sex-matched healthy controls (HC) underwent a conditioned pain modulation protocol. Cutaneous heat stimuli were delivered via laser evoked potentials (LEPs) on the dorsum of the right hand (UL) and foot (LL). N2 and P2 latencies, N2/P2 amplitude and pain ratings (NRS) were recorded before (baseline), during, and after a heterotopic noxious conditioning stimulation (HNCS) application. The baseline/HNCS ratio was calculated for both UL and LL.

RESULTS

N2 and P2 latencies did not vary between groups at each condition and limbs. Both groups showed a physiological N2/P2 amplitude and NRS reduction during the HNCS condition in UL and LL in comparison to baseline and post conditions (all, P < 0.003). Between-groups comparisons revealed a significant lower amplitude reduction in RLS at the N2/P2 amplitude during the HNCS condition only for LL (RLS, 13.6 μV; HC, 10.1 μV; P = 0.004). Such result was confirmed by the significant difference at the ratio (RLS, 69%, HC, 52.5%; P = 0.038).

CONCLUSIONS

The lower physiological reduction during the HNCS condition at LL in RLS patients suggests a defect in the endogenous inhibitory pain system. Further studies should clarify the causal link of this finding, also investigating the circadian modulation of this paradigm. © 2023 International Parkinson and Movement Disorder Society.

Test-Retest reliability and concurrent validity of novel nerve testing device for thermal detection and thermal pain thresholds

Thermal threshold testing is important for evaluating the thermal function of small-fibre nerve types C and A-delta. This study investigated the reliability and validity of a novel nerve testing device (NNTD) in evaluating thermal detection and thermal pain thresholds. Test-retest reliability of the NNTD and its concurrent validity compared to the current technology (Medoc TSA-2, Advanced Thermosensory Stimulator, Israel) were investigated among 10 healthy participants. Each participant was tested for the warm detection threshold (WDT), cold detection threshold (CDT), hot pain threshold (HPT) and cold pain threshold (CPT) on the medial forearm with NNTD for two trials and the Medoc TSA-2 for one trial over two consecutive days. Intraclass Correlation Coefficient values, Standard Error of Measurement and Bland Altman plots were calculated for test-retest reliability. One-way ANOVA and Bland Altman plots were calculated for validity. The test-retest reliability of the NNTD was good for CPT (ICC = 0.88), moderate for WDT (ICC = 0.545) and HPT (ICC = 0.710). The NNTD was valid for both trials of HPT and CPT and one trial for WDT compared to the Medoc TSA-2. In conclusion, the NNTD showed good to moderate reliability and was found to be valid compared to the Medoc TSA-2.

Myoclonus and other jerky movement disorders

Myoclonus and other jerky movements form a large heterogeneous group of disorders. Clinical neurophysiology studies can have an important contribution to support diagnosis but also to gain insight in the pathophysiology of different kind of jerks. This review focuses on myoclonus, tics, startle disorders, restless legs syndrome, and periodic leg movements during sleep. Myoclonus is defined as brief, shock-like movements, and subtypes can be classified based the anatomical origin. Both the clinical phenotype and the neurophysiological tests support this classification: cortical, cortical-subcortical, subcortical/non-segmental, segmental, peripheral, and functional jerks. The most important techniques used are polymyography and the combination of electromyography-electroencephalography focused on jerk-locked back-averaging, cortico-muscular coherence, and the Bereitschaftspotential. Clinically, the differential diagnosis of myoclonus includes tics, and this diagnosis is mainly based on the history with premonitory urges and the ability to suppress the tic. Electrophysiological tests are mainly applied in a research setting and include the Bereitschaftspotential, local field potentials, transcranial magnetic stimulation, and pre-pulse inhibition. Jerks due to a startling stimulus form the group of startle syndromes. This group includes disorders with an exaggerated startle reflex, such as hyperekplexia and stiff person syndrome, but also neuropsychiatric and stimulus-induced disorders. For these disorders polymyography combined with a startling stimulus can be useful to determine the pattern of muscle activation and thus the diagnosis. Assessment of symptoms in restless legs syndrome and periodic leg movements during sleep can be performed with different validated scoring criteria with the help of electromyography.

Exploring the role of the endogenous opiate system in the pathogenesis of anemia in an opiate receptor knock-out model of Restless Legs Syndrome

Restless Legs Syndrome (RLS) is characterized by bothersome leg discomfort accompanied by an urge to move to obtain relief and symptoms are worse at night and on lying down. There is at least partial and temporary relief with activity. It is also an opioid responsive disorder, often accompanied by iron deficiency with or without anemia, and inflammation may be a precipitating factor in some cases. We created two in-vivo opiate receptor knock out mouse models of RLS - a triple opiate receptor knock-out mouse and a mu opiate receptor knock-out mouse. Both sets of animals were restless during the sleep period as is also true of RLS. Both of our knockout models showed statistically significantly decreased Hemoglobin and Hematocrit indicating anemia and both models showed statistically significant decreases in serum iron suggestive of either iron deficiency anemia or inflammatory anemia. The rest of the hematologic studies were not consistent enough to determine which of these two types of anemia was present in either model. An additional experiment in normal wild type mice showed a statistically significant decrease in serum iron when an opiate receptor blocker was used. To our knowledge this is the first demonstration that deficiency of endogenous opioids might play a role in the production of anemia. Our hypothesis is that an intact endogenous opiate system is necessary for red cell homeostasis. The presence of opioid receptors both on red blood cells and on various immunologically based white blood cells suggest mechanisms by which deficiency in the endogenous opiate system could cause anemia of either the iron deficiency or inflammatory types. The administration of opioid agonists or antagonists to iron deficient cultures of red blood cell precursors is a next step in determining the role of the endogenous opiate system in the maintenance of red cell homeostasis and in the possible prevention of iron deficiency or inflammatory anemia where iron dysregulation is key.

Investigation of nerve fibers in the skin by biopsy: technical aspects, indications, and contribution to diagnosis of small-fiber neuropathy

Skin biopsy with investigation of small-diameter nerve fibers in human epidermis and dermis has been proven to be a useful method for confirming small-fiber neuropathy. In medical practice, small-fiber neuropathy is increasingly recognized as a leading cause of neuropathic pain. It is a prevalent complaint in medical offices, brought by patients often as a “painful burning sensation”. The prevalence of neuropathic pain is high in small-fiber neuropathies of different etiologies, especially in the elderly; 7% of population in this age group present peripheral neuropathy. Pain and paresthesia are symptoms which might cause disability and impair quality of life of patients. The early detection of small-fiber neuropathy can contribute to reducing unhealthy lifestyles, associated to higher incidence of the disease.

Restless Legs Syndrome: Known Knowns and Known Unknowns

Although restless legs syndrome (RLS) is a common neurological disorder, it remains poorly understood from both clinical and pathophysiological perspectives. RLS is classified among sleep-related movement disorders, namely, conditions characterized by simple, often stereotyped movements occurring during sleep. However, several clinical, neurophysiological and neuroimaging observations question this view. The aim of the present review is to summarize and query some of the current concepts (known knowns) and to identify open questions (known unknowns) on RLS pathophysiology. Based on several lines of evidence, we propose that RLS should be viewed as a disorder of sensorimotor interaction with a typical circadian pattern of occurrence, possibly arising from neurochemical dysfunction and abnormal excitability in different brain structures.

Signs of sympathetic and endothelial cell activation in the skin of patients with restless legs syndrome

OBJECTIVES

To evaluate skin biopsies of patients with early- and late onset restless legs syndrome (RLS) for concomitant small fiber neuropathy (SFN) and to determine cutaneous sympathetic innervation and microvascularization in comparison to healthy individuals.

METHODS

Density of intraepidermal nerve fibers (IENFD), adrenergic nerve fibers and dermal capillaries was analyzed by immunofluorescence for PGP9.5, tyrosine hydroxylase and endothelial markers CD31 and CD105 in skin biopsies of 11 individuals with RLS and 8 age- and sex-matched controls.

RESULTS

IENFD did not differ between RLS and controls, but two RLS patients with comorbid impaired glucose metabolism fulfilled morphometric criteria of SFN according to published normative values. In contrast, dermal nerve bundles of RLS patients showed an increased density of tyrosine hydroxylase⁺ adrenergic nerve fibers (p < 0.005). Moreover, an increased ratio between immature CD105⁺ and mature CD31⁺ endothelial cells within dermal capillaries was observed in RLS (p < 0.02).

CONCLUSIONS

SFN, as a potential contributing factor for RLS, should be considered in patients with predisposing comorbidities presenting with burning or shooting pain, dysesthesias and impaired sensory and temperature perception. Evidence of an increased adrenergic innervation of the skin in RLS patients is in accordance with sympathetic hyperactivity while signs of endothelial cell activation may reflect an adaptive response to tissue hypoxia.

Association between restless legs syndrome and peripheral neuropathy: A systematic review and meta-analysis

BACKGROUND AND PURPOSE

The coexistence of peripheral neuropathy (PN) and restless legs syndrome (RLS) or Willis-Ekbom disease is relatively frequent, but its prevalence has shown a high variability across studies. In addition, several reports have shown data suggesting the presence of PN in patients with idiopathic RLS.

METHODS

A search was undertaken using the PubMed, Embase and Web of Science Databases, from 1966 to 6 December 2020, crossing the search term 'restless legs syndrome' with 'neuropathy', 'polyneuropathy' (PNP) and 'peripheral neuropathy', and the references of interest for this topic were identified; a meta-analysis was performed, according to PRISMA guidelines, and a calculation of pooled prevalences, where appropriate, was made using standard methods.

RESULTS

Restless legs syndrome has been reported in 5.2%-53.7% of patients with PN (average 21.5%; 95% confidence interval 18.6%-24.5%), and PN has been reported in 0%-87.5% of patients with RLS (average 41.8%; 95% confidence interval 39.9%-43.6%), both being significantly more frequent than in controls. The heterogeneity across studies could be due to differences in the diagnostic criteria used for both RLS and PN. RLS is a frequent clinical complaint in patients with PN of different aetiologies, mainly diabetic PN, uraemic PNP, familial amyloid PNP, Charcot-Marie-Tooth disease and chronic dysimmune inflammatory PNP. Recent neurophysiological findings suggest the presence of small sensory fibre loss in patients diagnosed with idiopathic RLS, but it remains to be determined whether RLS associated with small sensory fibre loss and idiopathic RLS are different clinical entities.

CONCLUSIONS

Future studies including clinical and neurophysiological assessment and skin biopsy involving a large series of patients with PN and RLS are needed for a better understanding of the association between these two entities.

[Restless legs syndrome]

Restless legs syndrome (RLS) is seen widely in clinical practice. RLS commonly occurs at night time and presents with unpleasant or uncomfortable sensations in the legs that causes an urge to move them. This article describes the epidemiology, risk factors and pathophysiology of RLS. There is a detailed description of clinical presentations, diagnostic criteria and also management 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.

Restless legs syndrome induced by fexofenadine/pseudoephedrine

Antihistamines are known risk factors for restless legs syndrome (RLS). However, reports on RLS associated with fexofenadine or its combinations are rare. Here, we report a 30-year-old woman with RLS that was induced by fexofenadine/pseudoephedrine. She had been taking fexofenadine/pseudoephedrine for three months and felt a strong urge to move her legs at night, which was relieved by movement. Her condition improved by taking pramipexole, which she discontinued subsequently because of dizziness. One month later, she quitted taking fexofenadine/pseudoephedrine, after which her symptoms disappeared a week later. This case study demonstrates that RLS can be induced by fexofenadine/pseudoephedrine and we should always consider the possibility of drug-induced RLS.

The influence of restless legs symptoms on musculoskeletal pain in depression

Background and aims Restless legs syndrome is a sensorimotor disorder associated with mental health conditions notably depression. Restless legs symptoms and depression are commonly associated with pain. The study investigated the influence of restless legs symptoms on musculoskeletal pain in patients with depression or with increased depressive symptoms. Methods A cross-sectional study of primary care patients in the Central Finland Hospital District. The prevalence of restless legs symptoms was studied in patients with depressive symptoms (n = 695) and controls without a psychiatric diagnosis (n = 410) by using a structured questionnaire. The depressive symptoms were evaluated with the Beck Depression Inventory and the psychiatric diagnosis was confirmed by means of a diagnostic interview (MINI). The prevalence and intensity of musculoskeletal pain was captured with form-based questions. A single-question screen for restless legs symptoms was applied. Results There was a significant difference in the prevalence of continuous widespread musculoskeletal pain between the three study groups: the controls 4.6% (95% CI: 2.8-7.1), the patients with symptoms of depression without a diagnosis 16.0% (11.7-21.1), and the patients with diagnosed depression 22.1% (18.3-23.3) (p = 0.006 after being adjusted for age, sex, smoking, use of alcohol, education years, body mass index, use of antidepressants, and physical activity, after multiple corrections, all groups were significantly different from each other). Compared with those not having restless legs symptoms, subjects with restless legs symptoms had more often continuous widespread musculoskeletal pain in the control subjects (p = 0.001; 2.3% vs. 10.5%) and in the patients with depressive symptoms without a depression diagnosis (p = 0.024; 9.1 vs. 18.7%) but not in those with diagnosed depression (p = 0.98; 19.5 vs. 19.4%). The restless legs symptoms were associated with the intensity of pain in all groups (p < 0.001). Conclusions Restless legs symptoms were related to continuous widespread musculoskeletal pain in subjects without depressive symptoms and in patients with depressive symptoms without a depression diagnosis. Pain intensity was higher in the subjects with restless legs symptoms regardless of depressive symtoms or depression. Implications Clinical management of pain in patients with restless legs symptoms should include an increased focus on the prevention and treatment of either conditions.

BTBD9 and dopaminergic dysfunction in the pathogenesis of restless legs syndrome

Restless legs syndrome (RLS) is characterized by an urge to move legs, usually accompanied by uncomfortable sensations. RLS symptoms generally happen at night and can be relieved by movements. Genetic studies have linked polymorphisms in BTBD9 to a higher risk of RLS. Knockout of BTBD9 homolog in mice (Btbd9) and fly results in RLS-like phenotypes. A dysfunctional dopaminergic system is associated with RLS. However, the function of BTBD9 in the dopaminergic system and RLS is not clear. Here, we made use of the simple Caenorhabditis elegans nervous system. Loss of hpo-9, the worm homolog of BTBD9, resulted in hyperactive egg-laying behavior. Analysis of genetic interactions between hpo-9 and genes for dopamine receptors (dop-1, dop-3) indicated that hpo-9 and dop-1 worked similarly. Reporter assays of dop-1 and dop-3 revealed that hpo-9 knockout led to a significant increase of DOP-3 expression. This appears to be evolutionarily conserved in mice with an increased D₂ receptor (D₂R) mRNA in the striatum of the Btbd9 knockout mice. Furthermore, the striatal D₂R protein was significantly decreased and Dynamin I was increased. Overall, activities of DA neurons in the substantia nigra were not altered, but the peripheral D₁R pathway was potentiated in the Btbd9 knockout mice. Finally, we generated and characterized the dopamine neuron-specific Btbd9 knockout mice and detected an active-phase sleepiness, suggesting that dopamine neuron-specific loss of Btbd9 is sufficient to disturb the sleep. Our results suggest that increased activities in the D₁R pathway, decreased activities in the D₂R pathway, or both may contribute to RLS.

Mu opioid receptor knockout mouse: Phenotypes with implications on restless legs syndrome

Restless legs syndrome (RLS) is characterized by an irresistible need to move the legs while sitting or lying at night with insomnia as a frequent consequence. Human RLS has been associated with abnormalities in the endogenous opioid system, the dopaminergic system, the iron regulatory system, anemia, and inflammatory and auto-immune disorders. Our previous work indicates that mice lacking all three subtypes of opioid receptors have a phenotype similar to that of human RLS. To study the roles of each opioid receptor subtype in RLS, we first used mu opioid receptor knockout (MOR KO) mice based on our earlier studies using postmortem brain and cell culture. The KO mice showed decreased hemoglobin, hematocrit, and red blood cells (RBCs), with an appearance of microcytic RBCs indicating anemia. Together with decreased serum iron and transferrin, but increased ferritin levels, the anemia is similar to that seen with chronic inflammation in humans. A decreased serum iron level was also observed in the wildtype mice treated with an MOR antagonist. Iron was increased in the liver and spleen of the KO mice. Normal circadian variations in the dopaminergic and serotoninergic systems were absent in the KO mice. The KO mice showed hyperactivity and increased thermal sensitivity in wakefulness primarily during what would normally be the sleep phase similar to that seen in human RLS. Deficits in endogenous opioid system transmission could predispose to anemia of inflammation and loss of circadian variations in dopaminergic or serotonergic systems, thereby contributing to an RLS-like phenotype.

Quantitative sensory testing predicts histological small fiber neuropathy in postural tachycardia syndrome

Background

Retrospective investigation of the somatosensory profile and prediction of histologic small fiber neuropathy (SFN) in postural orthostatic tachycardia syndrome (POTS) was performed using quantitative sensory testing (QST) as a standardized noninvasive test.

Methods

In this investigation, full data sets from 30 patients (age: 34.03 ± 10.82 years, n = 6 males), including results of autonomic function testing, norepinephrine values, skin biopsy, and QST, were retrospectively analyzed. The QST data were compared with healthy controls (HCs) (age: 34.20 ± 10.5 years, n = 6 males, t test: 0.95).

Results

The evaluation of all QST parameters in POTS compared with HCs yielded differences in all thermal parameters (cold detection threshold: p < 0.05, warm detection threshold: p < 0.001, thermal sensory limen: p < 0.001, cold pain threshold: p < 0.05, and heat pain threshold: p < 0.001) and in paradoxical heat sensations (p < 0.05). Differences in nonpainful stimuli (mechanical detection threshold: p < 0.05 and vibration detection threshold: p < 0.001) were also detected. All patients who had clinical signs of SFN in combination with impairment of small fibers in QST also had SFN on skin biopsy.

Conclusion

These results suggest that a non-region-specific SFN in POTS compared with controls can be detected by noninvasive QST that predicts histologic small fiber pathology.

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

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

[Frequent neurological diseases associated with the restless legs syndrome]

BACKGROUND

Restless legs syndrome (RLS) is a common neurological disease. Studies have shown that RLS is associated with a variety of medical and neurological disorders.

OBJECTIVES

Using the example of three associated neurological diseases, the significance for everyday therapy decisions is assessed.

MATERIAL AND METHODS

A systematic search was carried out in PubMed for all studies with the keyword "RLS" in combination with polyneuropathies (PNP), Parkinson's disease (PD) and multiple sclerosis (MS) and classified according to the methodology in high, medium or low study quality.

RESULTS

Of 16 studies on RLS and MS, 10 were rated as "high". The high association frequency of RLS in MS between 13.3% and 65.1% (the variability possibly originates from different methods) prevents further statements about the prevalence. Within 30 studies on Parkinson's disease 17 were classified as having a high quality. In patients with Parkinson disease RLS occurs most frequently during therapy and is related to the duration of dopaminergic treatment. In patients with polyneuropathy, only 5 out of 24 studies were classified as being of high quality and an increased RLS prevalence was detected for acquired polyneuropathies with heterogeneous data for hereditary forms.

CONCLUSION

There is an increased prevalence of association with RLS for the diseases discussed. This prevalence is possibly determined by the pathophysiology of these disorders. These diseases are possibly characterized by genetic predispositions as well, which can hopefully be classified more accurately in the future.

Hyperactivity, dopaminergic abnormalities, iron deficiency and anemia in an in vivo opioid receptors knockout mouse: Implications for the restless legs syndrome

Previous studies have uncovered a potential role of the opioid system in iron hemostasis and dopamine metabolism. Abnormalities in both of these systems have been noted in human RLS. Autopsy studies of human RLS have shown an endogenous opioid deficiency in the thalamus. Opioids, particularly prolonged-release oxycodone/naloxone, have been approved in Europe to be a second-line therapy for severe restless legs syndrome (RLS). To study the role of opioid receptors in the pathogenesis of RLS, we used a triple knockout (KO) mouse strain that lack mu, delta, and kappa opioid receptors and explored the behavioral and biochemical parameters relevant to RLS. The triple KO mice showed hyperactivity and a trend of increased probability of waking during the rest period (day) akin to that in human RLS (night). Surprisingly, triple KO mice also exhibit decreased serum iron concentration, evidence of anemia, a significant dysfunction in dopamine metabolism akin to that noted in human RLS, as well as an increased latency in response to thermal stimuli. To our knowledge, this is the first study to demonstrate that the endogenous opioid system may play a role in iron metabolism and subsequently in the pathogenesis of anemia. It is also the first study showing that opioid receptors are involved in the production of motor restlessness with a circadian predominance. Our findings support the role of endogenous opioids in the pathogenesis of RLS, and the triple KO mice can be used to understand the relationship between iron deficiency, anemia, dopaminergic dysfunction, and RLS.

Itch Processing in the Skin

Itching can result from activity of specialized primary afferent neurons (“pruriceptors”) that have been shown to express certain molecular markers such as B-type natriuretic peptide and several members of the Mrgpr-family in rodents. On the other hand, neurons involved in pain processing (“nociceptors”) can also provoke itching when the activation site is restricted to an isolated tiny spot within the epidermis. Individuals classified as having sensitive skin report increased itching and pain sensations upon weak external stimuli that are not painful or itchy in the control group. Numerous possible factors could contribute to sensitive skin along the pathway of transduction of the external stimuli into peripheral neuronal signals, followed by neuronal processing, finally resulting in the perception: (a) reduced local protective factors leading to impaired skin barrier function, (b) increased production of excitatory skin mediators, (c) sensitized peripheral neurons, (d) facilitated spinal and central processing, and (e) reduced descending inhibition from the central nervous system. For all of those pathophysiological mechanisms there are clinical examples such as atopic dermatitis (a,b,c), neuropathic itching (c,e), and restless leg syndrome (d,e). However, none of these factors have been directly linked to the occurrence of sensitive skin. Moreover, individuals reporting sensitive skin are heterogeneous and a subpopulation with defined pathophysiology has not yet been identified. Given that the condition is reported in about 50% of women, and thereby includes many healthy individuals, it appears problematic to assign a definitive pathophysiological mechanism to it.

Restless legs syndrome: Clinical changes in nervous system excitability at the spinal cord level

Restless legs syndrome (RLS) is a complex multifactorial disorder whose aetiology has yet to be fully elucidated. Some of the features of RLS, such as processing of sensations and activation of movement, may result from a dysfunction in spinal processing giving rise to a state of spinal hyperexcitability. In the current article we review studies investigating spinal excitability in RLS patients looking specifically at electrophysiological studies of spinal activity, sensory evaluations, and spinal reflex studies. Increased spinal excitability has been shown in RLS patients based on the combined data from electrophysiological studies. Results from studies assessing sensory evaluations in RLS patients show enhanced spinal processing of nociceptive inputs possibly due to central sensitisation. However, not all sensory modalities demonstrate an increase in sensitivity. An increase in nervous system excitability would result in an increase in reflex responses in RLS patients however the data from reflex analyses in RLS patients has failed to consistently show this expected result. Overall changes to RLS spinal excitability have been demonstrated though these changes might be heterogeneous as not all afferent input appears to be affected in the same manner. There may be phase-dependent and modality-dependent alterations in spinal excitability suggesting that the theory of absolute spinal hyperexcitability in RLS patients' needs to be reconsidered.

The Clinical Features of Painful Small-Fiber Neuropathy Suggesting an Origin Linked to Primary Sjögren's Syndrome

OBJECTIVE

We attempted to determine whether clinical features could differentiate painful small-fiber neuropathy related to primary Sj€ogren's syndrome (pSS-SFN) from idiopathic SFN (idio-SFN).

METHODS

Validated clinical questionnaires and neurophysiological investigations specific for pain and SFN assessment were performed in 25 patients with pSS-SFN and 25 patients with idio-SFN.

RESULTS

Patients with idio-SFN had more frequent severe burning sensations and higher mean anxiety scores and daily pain intensity compared to patients with pSSSFN. Conversely, patients with pSS-SFN had reduced electrochemical skin conductance measured by Sudoscan_, and almost half of them had the sensation of walking on cotton wool.

CONCLUSION

Our results suggest that idio-SFN more specifically involved small sensory fibers than pSS-SFN, in which subtle dysfunction of larger sensory fibers and damage of distal autonomic sudomotor innervation may occur. A practical algorithm is proposed to help to differentiate SFN associated with pSS from idio-SFN, based on information very easy to obtain by clinical interview.

Ih contributes to increased motoneuron excitability in restless legs syndrome

KEY POINTS

Restless legs patients complain about sensory and motor symptoms leading to sleep disturbances. Symptoms include painful sensations, an urge to move and involuntary leg movements. The responsible mechanisms of restless legs syndrome are still not known, although current studies indicate an increased neuronal network excitability. Reflex studies indicate the involvement of spinal structures. Peripheral mechanisms have not been investigated so far. In the present study, we provide evidence of increased hyperpolarization-activated cyclic nucleotide-gated (HCN) channel-mediated inward rectification in motor axons. The excitability of sensory axons was not changed. We conclude that, in restless legs syndrome, an increased HCN current in motoneurons may play a pathophysiological role, such that these channels could represent a valuable target for pharmaceutical intervention.

ABSTRACT

Restless legs syndrome is a sensorimotor network disorder. So far, the responsible pathophysiological mechanisms are poorly understood. In the present study, we provide evidence that the excitability of peripheral motoneurons contributes to the pathophysiology of restless legs syndrome. In vivo excitability studies on motor and sensory axons of the median nerve were performed on patients with idiopathic restless legs syndrome (iRLS) who were not currently on treatment. The iRLS patients had greater accommodation in motor but not sensory axons to long-lasting hyperpolarization compared to age-matched healthy subjects, indicating greater inward rectification in iRLS. The most reasonable explanation is that hyperpolarization-activated cyclic nucleotide-gated (HCN) channels open at less hyperpolarized membrane potentials, a view supported by mathematical modelling. The half-activation potential for HCN channels (Bq) was the single best parameter that accounted for the difference between normal controls and iRLS data. A 6 mV depolarization of Bq reduced the discrepancy between the normal control model and the iRLS data by 92.1%. Taken together, our results suggest an increase in the excitability of motor units in iRLS that could enhance the likelihood of leg movements. The abnormal axonal properties are consistent with other findings indicating that the peripheral system is part of the network involved in iRLS.

French Consensus: How to diagnose restless legs syndrome

Correct diagnosis of restless legs syndrome (RLS) is essential to patient care and treatment. Diagnosis is most often clinical and based on diagnostic criteria: the need to move the legs accompanied to varying degrees by unpleasant sensations, predominantly during the evening and improved by movement. In rare cases, clinical examination is insufficient and a polysomnography is necessary. Once a positive diagnosis has been made, a neurological examination and an assessment of iron status are required. The severity of the RLS must be evaluated to determine whether a specific treatment is necessary. Before treatment, it is essential to ensure that a definite diagnosis of RLS has been made and the phenotype characterised. This enables a personal treatment plan and limits the risk of augmentation syndrome.

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.

Distal muscle activity alterations during the stance phase of gait in restless leg syndrome (RLS) patients

OBJECTIVE

To assess if there is a circadian variation in electromyographical (EMG) muscle activity during gait in restless legs syndrome (RLS) patients and healthy control participants.

METHODS

Gait assessment was done in 14 RLS patients and 13 healthy control participants in the evening (PM) and the morning (AM). Muscle activity was recorded bilaterally from the tibialis anterior (TA), lateral gastrocnemius (GL), rectus femoris (RF) and biceps femoris (BF) muscles.

RESULTS

A circadian variation during the stance phase in only TA (PM > AM, p < 0.005) and BF (PM < AM, p = 0.008) activity was observed in control participants. Conversely no circadian variation was seen in any muscles in the RLS patients. RLS patients had an increased TA and GL activity (RLS > Controls, p < 0.05) during early stance and decreased GL activity (RLS < Controls, p < 0.01) during terminal stance in comparison to control participants in the evening. No other significant differences were noted between RLS patients and control participants. Activation of GL during the swing phase was noted in 79% of RLS patients and in 23% of control participants in the morning compared to 71% and 38% in the evening, respectively.

CONCLUSION

EMG muscle activity shows no circadian variation in RLS patients. Evening differences in gait muscle activation patterns between RLS patients and control participants are evident. These results extend our knowledge about alterations in spinal processing during gait in RLS. A possible explanation for these findings is central pattern generator sensitization caused by increased sensitivity in cutaneous afferents in RLS patients.

The Association Between Vitamin D Level and Restless Legs Syndrome: A Population-Based Case-Control Study

STUDY OBJECTIVES

The pathophysiology of restless legs syndrome (RLS) may be related to abnormalities in central dopamine pathways. Vitamin D may play a role in the pathophysiology of RLS by modulating the dopaminergic system. The aim of our study is to examine the possible link between RLS and vitamin D deficiency.

METHODS

The total number of subjects enrolled was 201, including 78 patients with RLS based on the International RLS Study Group (IRLSSG) diagnostic criteria and 123 controls. Serum 25-hydroxy vitamin D levels were measured in both groups. RLS severity was assessed in all cases using the IRLSSG symptom severity rating scale.

RESULTS

Fifty-nine patients with RLS (75.6%) and 52 controls (42.3%) had a diagnosis of vitamin D deficiency, P < .001. The odds ratio (OR) of the development of RLS was 4.24 for those with a vitamin D level < 50 nmol/L compared to those with a vitamin D level ≥ 50 nmol/L (P < .001, 95% confidence interval [CI] 2.3-7.9). After adjusting for all other significant factors in the multivariate logistic model, vitamin D was significantly associated with RLS (OR 3.1, P < .002, 95% CI 1.51-6.38). Moreover, a dark or black skin color (OR 3.4, P < .001, 95% CI 1.5-6.3) and working as a teacher (OR 8.8, P < .001, 95% CI 3.4-23.5) were also independently significantly associated with RLS.

CONCLUSIONS

Our study identified an association between vitamin D deficiency and RLS. Consequently, vitamin D deficiency should be considered in the management of RLS. However, further studies are needed to evaluate the causality relationship between vitamin D level and RLS.

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.

Meis1: effects on motor phenotypes and the sensorimotor system in mice

MEIS1 encodes a developmental transcription factor and has been linked to restless legs syndrome (RLS) in genome-wide association studies. RLS is a movement disorder leading to severe sleep reduction and has a substantial impact on the quality of life of patients. In genome-wide association studies, MEIS1 has consistently been the gene with the highest effect size and functional studies suggest a disease-relevant downregulation. Therefore, haploinsufficiency of Meis1 could be the system with the most potential for modeling RLS in animals. We used heterozygous Meis1-knockout mice to study the effects of Meis1 haploinsufficiency on mouse behavioral and neurological phenotypes, and to relate the findings to human RLS. We exposed the Meis1-deficient mice to assays of motor, sensorimotor and cognitive ability, and assessed the effect of a dopaminergic receptor 2/3 agonist commonly used in the treatment of RLS. The mutant mice showed a pattern of circadian hyperactivity, which is compatible with human RLS. Moreover, we discovered a replicable prepulse inhibition (PPI) deficit in the Meis1-deficient animals. In addition, these mice were hyposensitive to the PPI-reducing effect of the dopaminergic receptor agonist, highlighting a role of Meis1 in the dopaminergic system. Other reported phenotypes include enhanced social recognition at an older age that was not related to alterations in adult olfactory bulb neurogenesis previously shown to be implicated in this behavior. In conclusion, the Meis1-deficient mice fulfill some of the hallmarks of an RLS animal model, and revealed the role of Meis1 in sensorimotor gating and in the dopaminergic systems modulating it.

Summary: Loss of Meis1 results in motor restlessness in mice, a phenotype resembling human restless legs syndrome, as well as altered sensorimotor gating and improved social discrimination memory.

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.

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.

Dopaminergic treatment of restless legs syndrome in spinal cord injury patients with neuropathic pain

Recent studies report high incidence of restless legs syndrome (RLS) in patients with spinal cord injury (SCI), who may also present pain and sensory disturbances. In the present manuscript, we examine and discuss diagnostic and treatment challenges of comorbid RLS and neuropathic pain (NP) in SCI. We evaluated seven men with a mean age of 55.6 (s.d.=14.0) years, with chronic complete or incomplete SCI at the thoracic or lumbar level, for complaints of sensory disturbances in the legs, which initially were attributed to drug-resistant NP. Because overlapped RLS was suspected, clinical evaluation of NP and RLS, serum ferritin and iron level assessment, and video polysomnographic (VPSG) studies were conducted. Pramipexole (0.18 mg q.d.^-1) was added to treat RLS, and a follow-up was performed at 2 months. We found that in six subjects the RLS was comorbid with NP and in one subject the symptoms of RLS were misdiagnosed as NP. VPSG revealed periodic limb movements (PLMs) in all patients, including PLMs of the legs, arms or both. Serum ferritin was <50 ng ml^-1 in two patients. RLS improved significantly after 2 months with pramipexole. On the basis of current findings, we recommend physicians to be aware of the comorbidity between RLS and NP secondary to SCI to include suitable diagnostic procedures and effective treatments.

"Emplotted Narratives" and Structured "Behavioral Observations" Supporting the Diagnosis of Willis-Ekbom Disease/Restless Legs Syndrome in Children with Neurodevelopmental Conditions

Background

Willis‐Ekbom disease/restless legs syndrome (WED/RLS) seems to be a frequent cause of intractable chronic insomnia (ICI) but is under‐recognized in children/adolescents with neurodevelopmental conditions (NDCs), as many patients do not have the ability to express the underlying “urge‐to‐move”. In light of this, we aim to develop a protocol for behavioral observations supporting the diagnosis of WED/RLS.

Methods

We investigated 26 pediatric patients (age 1–16 years, median 8) with NDCs, ICI and evidence of familial WED/RLS employing (1) “emplotted narratives” for description of the various “urge‐to‐move” presentations and (2) self‐description and “behavioral observations” during a “suggested clinical immobilization test” (SCIT).

Results

Parental narratives reflected typical WED/RLS‐related “urge‐to‐move” symptoms during day‐, bed‐, and nighttime in all patients. Fifteen out of 26 patients could describe the “urge‐to‐move” during the SCIT. Ten out of 26 patients, unable to describe their symptoms due to cognitive disabilities, showed patterns of “relieving‐movements” upon observation. Sensory processing abnormalities were reported in all patients, with tactile sensitivities (26/26) (including shifted pain threshold) as the most common sensory domain.

Conclusion

“Emplotted narratives” and structured “behavioral observations” support recognition of familial WED/RLS associated movement patterns and provide a useful tool for the diagnosis of WED/RLS in children with NDCs in a clinical office setting.

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

STUDY OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Clinical Ratings of Pain Sensitivity Correlate With Quantitative Measures in People With Chronic Neck Pain and Healthy Controls: Cross-Sectional Study

BACKGROUND

Correlations between clinical and quantitative measures of pain sensitivity are poor, making it difficult for clinicians to detect people with pain sensitivity. Clinical detection of pain sensitivity is important because these people have a different prognosis and may require different treatment.

OBJECTIVE

The purpose of this study was to investigate the relationship between clinical and quantitative measures of pain sensitivity across individuals with and without neck pain.

METHODS

This cross-sectional study included 40 participants with chronic neck pain and 40 age- and sex-matched controls. Participants underwent quantitative sensory testing of cold pain thresholds (CPTs) and pressure pain thresholds (PPTs). Clinical tests for pain sensitivity were the ice pain test and the pressure pain test. All tests were undertaken at standardized local (neck and upper trapezius muscles) and remote (wrist and tibialis anterior muscles) sites. Median and interquartile range (IQR) were calculated for neck pain and control groups, and parametric and nonparametric tests were used to compare groups. Correlation coefficients were calculated between quantitative and clinical measures.

RESULTS

There were significant differences for clinical and quantitative measures of cold and pressure sensitivity between the neck pain and control groups (eg, CPT neck pain group: median=22.31°C, IQR=18.58°C; control group: median=5.0°C, IQR=0.74°C). Moderate-to-good correlations were found between the clinical ice pain test and CPT at all sites (.46 to .68) except at the wrist (.29 to .40). Fair correlations were found for the clinical pressure pain test and PPT (-.26 to -.45). Psychological variables contributing to quantitative measures of pain sensitivity included catastrophization, sleep quality, and female sex.

LIMITATIONS

Clinical pressure pain tests were not quantitatively standardized in this study.

CONCLUSIONS

The ice pain test may be useful as a clinical correlate of CPT at all sites except the wrist, whereas the pressure pain test is less convincing as a clinical correlate of PPT.

Transcutaneous spinal DC stimulation reduces pain sensitivity in humans

Non-invasive approaches to pain management are needed to manage patient pain escalation and to providing sufficient pain relief. Here, we evaluate the potential of transcutaneous spinal direct current stimulation (tsDCS) to modulate pain sensitivity to electrical stimuli and mechanical pinpricks in 24 healthy subjects in a sham-controlled, single-blind study. Pain ratings to mechanical pinpricks and electrical stimuli were recorded prior to and at three time points (0, 30, and 60min) following 15min of anodal tsDCS (2.5mA, "active" electrode centered over the T11 spinous process, return electrode on the left posterior shoulder). Pain ratings to the pinpricks of the highest forces tested (128, 256, 512mN) were reduced at 30min and 60min following anodal tsDCS. These findings demonstrate that pain sensitivity in healthy subjects can be suppressed by anodal tsDCS and suggest that tsDCS may provide a non-invasive tool to manage mechanically-induced pain.

Depolarized inactivation overcomes impaired activation to produce DRG neuron hyperexcitability in a Nav1.7 mutation in a patient with distal limb pain

Sodium channel Nav1.7, encoded by SCN9A, is expressed in DRG neurons and regulates their excitability. Genetic and functional studies have established a critical contribution of Nav1.7 to human pain disorders. We have now characterized a novel Nav1.7 mutation (R1279P) from a female human subject with distal limb pain, in which depolarized fast inactivation overrides impaired activation to produce hyperexcitability and spontaneous firing in DRG neurons. Whole-cell voltage-clamp recordings in human embryonic kidney (HEK) 293 cells demonstrated that R1279P significantly depolarizes steady-state fast-, slow-, and closed-state inactivation. It accelerates deactivation, decelerates inactivation, and facilitates repriming. The mutation increases ramp currents in response to slow depolarizations. Our voltage-clamp analysis showed that R1279P depolarizes channel activation, a change that was supported by our multistate structural modeling. Because this mutation confers both gain-of-function and loss-of-function attributes on the Nav1.7 channel, we tested the impact of R1279P expression on DRG neuron excitability. Current-clamp studies reveal that R1279P depolarizes resting membrane potential, decreases current threshold, and increases firing frequency of evoked action potentials within small DRG neurons. The populations of spontaneously firing and repetitively firing neurons were increased by expressing R1279P. These observations indicate that the dominant proexcitatory gating changes associated with this mutation, including depolarized steady-state fast-, slow-, and closed-state inactivation, faster repriming, and larger ramp currents, override the depolarizing shift of activation, to produce hyperexcitability and spontaneous firing of nociceptive neurons that underlie pain.