Pramipexole alters thermoregulation in restless legs syndrome

STUDY OBJECTIVES

Previous studies have associated restless legs syndrome (RLS) with peripheral hypoxia and impaired thermoregulation in the lower extremities. We performed long-term monitoring of skin temperatures in order to investigate whether these findings could be explained by reduced blood flow to the peripheral tissues.

METHODS

96-hour continuous measurements of skin temperature were performed both in the distal and proximal parts of the body of 15 patients with RLS and 14 healthy controls. During the recording, the patients participated in suggested immobilization tests both with and without pramipexole medication.

RESULTS

We found no baseline differences in distal or proximal skin temperature between patients and controls in daytime or during immobilization. However, pramipexole significantly increased distal skin temperature in the patient group during immobilization (31.1°C vs. 32.9°C, p < 0.05). Daytime temperatures were not affected by therapy or disease status.

CONCLUSIONS

The data suggest that patients with RLS and healthy controls have similar blood flow to the peripheral skin tissue. Pramipexole, however, alters thermoregulation and the previous studies might have been biased by medication. Dopaminergic medication is a major confounding factor when assessing peripheral phenomena in RLS and should be controlled for in the future studies.

Restless legs syndrome/Willis-Ekbom disease diagnostic criteria: updated International Restless Legs Syndrome Study Group (IRLSSG) consensus criteria--history, rationale, description, and significance

BACKGROUND

In 2003, following a workshop at the National Institutes of Health, the International Restless Legs Syndrome Study Group (IRLSSG) developed updated diagnostic criteria for restless legs syndrome/Willis-Ekbom disease (RLS/WED). These criteria were integral to major advances in research, notably in epidemiology, biology, and treatment of RLS/WED. However, extensive review of accumulating literature based on the 2003 NIH/IRLSSG criteria led to efforts to improve the diagnostic criteria further.

METHODS

The clinical standards workshop, sponsored by the WED Foundation and IRLSSG in 2008, started a four-year process for updating the diagnostic criteria. That process included a rigorous review of research advances and input from clinical experts across multiple disciplines. After broad consensus was attained, the criteria were formally approved by the IRLSSG executive committee and membership.

RESULTS

Major changes are: (i) addition of a fifth essential criterion, differential diagnosis, to improve specificity by requiring that RLS/WED symptoms not be confused with similar symptoms from other conditions; (ii) addition of a specifier to delineate clinically significant RLS/WED; (iii) addition of course specifiers to classify RLS/WED as chronic-persistent or intermittent; and (iv) merging of the pediatric with the adult diagnostic criteria. Also discussed are supportive features and clinical aspects that are important in the diagnostic evaluation.

CONCLUSIONS

The IRLSSG consensus criteria for RLS/WED represent an international, interdisciplinary, and collaborative effort intended to improve clinical practice and promote further research.

One night of total sleep deprivation promotes a state of generalized hyperalgesia: a surrogate pain model to study the relationship of insomnia and pain

Sleep disturbances are highly prevalent in chronic pain patients. Understanding their relationship has become an important research topic since poor sleep and pain are assumed to closely interact. To date, human experimental studies exploring the impact of sleep disruption/deprivation on pain perception have yielded conflicting results. This inconsistency may be due to the large heterogeneity of study populations and study protocols previously used. In addition, none of the previous studies investigated the entire spectrum of nociceptive modalities. To address these shortcomings, a standardized comprehensive quantitative sensory protocol was used in order to compare the somatosensory profile of 14 healthy subjects (6 female, 8 male, 23.5 ± 4.1 year; mean ± SD) after a night of total sleep deprivation (TSD) and a night of habitual sleep in a cross-over design. One night of TSD significantly increased the level of sleepiness (P<0.001) and resulted in higher scores of the State Anxiety Inventory (P<0.01). In addition to previously reported hyperalgesia to heat (P<0.05) and blunt pressure (P<0.05), study participants developed hyperalgesia to cold (P<0.01) and increased mechanical pain sensitivity to pinprick stimuli (P<0.05) but no changes in temporal summation. Paradoxical heat sensations or dynamic mechanical allodynia were absent. TSD selectively modulated nociception, since detection thresholds of non-nociceptive modalities remained unchanged. Our findings show that a single night of TSD is able to induce generalized hyperalgesia and to increase State Anxiety scores. In the future, TSD may serve as a translational pain model to elucidate the pathomechanisms underlying the hyperalgesic effect of sleep disturbances.

Alterations in endogenous pain modulation in endurance athletes: an experimental study using quantitative sensory testing and the cold-pressor task

There is evidence for long-term alterations in pain tolerance among athletes compared with normally active controls. However, scientific data on pain thresholds in this population are inconsistent, and the underlying mechanisms for the differences remain unclear. Therefore, we assessed differences and similarities in pain perception and conditioned pain modulation (CPM) at rest in endurance athletes and normally active controls. The standardised quantitative sensory testing protocol (QST) of the 'German-Research-Network-on-Neuropathic-Pain' was used to obtain comprehensive profiles on somatosensory functions. The protocol consisted of thermal and mechanical detection as well as pain thresholds, vibration thresholds, and pain sensitivity to sharp and blunt mechanical stimuli. CPM (the diffuse-noxious-inhibitory-control-like effect) was measured using 2 tonic heat pain test stimuli (at the temperature exceeding a subjective pain rating of 50/100) separated by a 2-min cold-pressor task (CPM-TASK; conditioning stimulus). Pain ratings were measured with a numerical rating scale. Endurance capacity was validated by assessment of maximum oxygen uptake (VO2max). Participants included 25 pain-free male endurance athletes (VO2max>60mL/min∗kg) and 26 pain-free normally active controls (VO2max<45mL/min∗kg) matched based on age and body mass index. Athletes were significantly less sensitive to mechanical pain but showed higher sensitivity to vibration (P<0.05). In athletes, CPM was significantly less activated by the conditioning stimuli (P<0.05) when compared with normally active controls. Our data show that somatosensory processing in athletes differs in comparison with controls, and suggest that the endogenous pain inhibitory system may be less responsive. This finding may explain the paradoxical propensity of athletes to develop chronic widespread pain.

Quantitative thermal sensory testing and sympathetic skin response in primary Restless legs syndrome - A prospective study on 57 Indian patients

Patients with restless leg syndrome present with sensory symptoms similar to peripheral neuropathy. While there is evidence of abnormalities of dopaminergic pathways, the peripheral nervous system has been studied infrequently. We studied conventional nerve conduction studies, quantitative thermal sensory testing and sympathetic skin response in 57 patients with primary restless leg syndrome. Almost two third patients demonstrated abnormalities in the detailed testing of the peripheral nervous system. Sbtle abnormalities of the peripheral nervous system may be more common than previously believed.

The cutaneous nerve biopsy: technical aspects, indications, and contribution

Skin biopsy with a 3mm disposable circular punch is easy to perform and allows, after proper processing, the visualization of epidermal, dermal, and sweat gland nerve fibers. A technique of sampling the epidermis alone by applying a suction capsule, the "blister" technique, has also been developed. It is most common to stain immunohistochemically for the pan-axonal marker protein gene product 9.5 (PGP 9.5), an ubiquitin C-terminal hydroxylase. The sections are then observed and analyzed with bright-field microscopy or with indirect immunofluorescence with or without confocal microscopy. Most studies report quantification of intraepidermal nerve fiber density displayed in bright-field microscopy. Normative values have been established, particularly from the distal part of the leg, 10cm above the external malleolus. In diabetes mellitus early degeneration of intraepidermal nerve fibers is induced and there is slower regeneration even when there is no evidence of neuropathy. Skin biopsy is of particular value in the diagnosis of small fiber neuropathy when nerve conduction studies are normal. It may also be repeated in order to study the progressive nature of the disease and also has the potential of studying regeneration of nerve fibers and thus the effects of treatment. Inflammatory demyelinating neuropathies may also involve loss of small-diameter nerve fibers and IgM deposits in dermal myelinated nerve fibers in anti-MAG neuropathy. In some cases the presence of vasculitis in skin may indicate a nonsystemic vasculitic neuropathy and in HIV neuropathy intraepidermal nerve fiber density is reduced in a length-dependent manner. In several hereditary neuropathies intraepidermal nerve fiber density may be reduced but other abnormalities can also be demonstrated in dermal myelinated fibers. Some small swellings and varicosities may be present in the distal leg skin biopsy of healthy individuals but large axonal swellings are considered as evidence of a pathological process affecting the normal structure of nerves. The indirect immunofluorescence technique with confocal microscopy provides the opportunity to study the complex structure of sensory receptors and cutaneous myelinated fibers and the innervation of sweat glands, arrector pilorum muscles, and vessels.

Abnormal medial thalamic metabolism in patients with idiopathic restless legs syndrome

Pathophysiology of restless legs syndrome is poorly understood. A role of the thalamus, specifically of its medial portion which is a part of the limbic system, was suggested by functional magnetic resonance imaging and positron emission tomography studies. The aim of this study was to evaluate medial thalamus metabolism and structural integrity in patients with idiopathic restless legs syndrome using a multimodal magnetic resonance approach, including proton magnetic resonance spectroscopy, diffusion tensor imaging, voxel-based morphometry and volumetric and shape analysis. Twenty-three patients and 19 healthy controls were studied in a 1.5 T system. Single voxel proton magnetic resonance spectra were acquired in the medial region of the thalamus. In diffusion tensor examination, mean diffusivity and fractional anisotropy were determined at the level of medial thalamus using regions of interest delineated to outline the same parenchyma studied by spectroscopy. Voxel-based morphometry was performed focusing the analysis on the thalamus. Thalamic volumes were obtained using FMRIB's Integrated Registration and Segmentation Tool software, and shape analysis was performed using the FMRIB Software Library tools. Proton magnetic resonance spectroscopy study disclosed a significantly reduced N-acetylaspartate:creatine ratio and N-acetylaspartate concentrations in the medial thalamus of patients with restless legs syndrome compared with healthy controls (P < 0.01 for both variable). Lower N-acetylaspartate concentrations were significantly associated with a family history of restless legs syndrome (β = -0.49; P = 0.018). On the contrary, diffusion tensor imaging, voxel-based morphometry and volumetric and shape analysis of the thalami did not show differences between the two groups. Proton magnetic resonance spectroscopic findings in patients with restless legs syndrome indicate an involvement of medial thalamic nuclei of a functional nature; however, the other structural techniques of the same region did not show any changes. These findings support the hypothesis that dysfunction of the limbic system plays a role in the pathophysiology of idiopathic restless legs syndrome.

Quantitative sensory testing of neuropathic pain patients: potential mechanistic and therapeutic implications

Quantitative sensory testing (QST) is a widely accepted tool to investigate somatosensory changes in pain patients. Many different protocols have been developed in clinical pain research within recent years. In this review, we provide an overview of QST and tested neuroanatomical pathways, including peripheral and central structures. Based on research studies using animal and human surrogate models of neuropathic pain, possible underlying mechanisms of chronic pain are discussed. Clinically, QST may be useful for 1) the identification of subgroups of patients with different underlying pain mechanisms; 2) prediction of therapeutic outcomes; and 3) quantification of therapeutic interventions in pain therapy. Combined with sensory mapping, QST may provide useful information on the site of neural damage and on mechanisms of positive and negative somatosensory abnormalities. The use of QST in individual patients for diagnostic purposes leading to individualized therapy is an interesting concept, but needs further validation.

Subgroups of musculoskeletal pain patients and their psychobiological patterns - the LOGIN study protocol

BACKGROUND

Pain conditions of the musculoskeletal system are very common and have tremendous socioeconomic impact. Despite its high prevalence, musculoskeletal pain remains poorly understood and predominantly non-specifically and insufficiently treated.The group of chronic musculoskeletal pain patients is supposed to be heterogeneous, due to a multitude of mechanisms involved in chronic pain. Psychological variables, psychophysiological processes, and neuroendocrine alterations are expected to be involved. Thus far, studies on musculoskeletal pain have predominantly focused on the general aspects of pain processing, thus neglecting the heterogeneity of patients with musculoskeletal pain. Consequently, there is a need for studies that comprise a multitude of mechanisms that are potentially involved in the chronicity and spread of pain. This need might foster research and facilitate a better pathophysiological understanding of the condition, thereby promoting the development of specific mechanism-based treatments for chronic pain. Therefore, the objectives of this study are as follows: 1) identify and describe subgroups of patients with musculoskeletal pain with regard to clinical manifestations (including mental co-morbidity) and 2) investigate whether distinct sensory profiles or 3) distinct plasma levels of pain-related parameters due to different underlying mechanisms can be distinguished in various subgroups of pain patients.

METHODS/DESIGN

We will examine a population-based chronic pain sample (n = 100), a clinical tertiary care sample (n = 100) and pain-free patients with depression or post-traumatic stress disorder and pain-free healthy controls (each n = 30, respectively). The samples will be pain localisation matched by sex and age to the population-based sample. Patients will undergo physical examination and thorough assessments of mental co-morbidity (including psychological trauma), perceptual and central sensitisation (quantitative sensory testing), descending inhibition (conditioned pain modulation, the diffuse noxious inhibitory control-like effect), as well as measurement of the plasma levels of nerve growth factor and endocannabinoids.

DISCUSSION

The identification of the underlying pathophysiologic mechanisms in different subgroups of chronic musculoskeletal pain patients will contribute to a mechanism-based subgroup classification. This will foster the development of mechanism-based treatments and holds promise to treat patients more sufficient.

Dopa responsive burning mouth syndrome: restless mouth syndrome or oral variant of restless legs syndrome?

Burning mouth syndrome (BMS) is an oral dysesthesia presenting as a burning sensation of the tongue and other oral and perioral mucosae. A painful symptomatology in different bodily regions (extraoral) may also be a common feature in patient with BMS. The management of BMS is challenging and there is no clear guideline for the management of idiopathic BMS. Herein, we describe a group of patients (5 patients) in whom symptoms of BMS responded to levodopa. In parallel, four patients fulfilled the criteria for restless legs syndrome (RLS). Family history of RLS was positive in two patients. We reviewed the literature and noted a marked overlap between BMS and RLS. Overlaps were noted in epidemiological profiles, pattern of clinical features and even in neurophysiological observations (alterations in the striatal dopaminergic system). We suggest that a subset of patients with BMS may be a phenotypic variant of RLS and a trial of dopaminergic drugs should be given in patients with BMS who has a history suggestive of RLS or in a patient who do not show a response to usual therapies for BMS.

Motor restlessness, sleep disturbances, thermal sensory alterations and elevated serum iron levels in Btbd9 mutant mice

Restless legs syndrome (RLS), also known as Willis-Ekbom disease, is a sensory-motor neurological disorder with a circadian component. RLS is characterized by uncomfortable sensations in the extremities, generally at night or during sleep, which often leads to an uncontrollable urge to move them for relief. Recently, genomic studies identified single-nucleotide polymorphisms in BTBD9, along with three other genes, as being associated with a higher risk of RLS. Little is known about the function of BTBD9 or its potential role in the pathophysiology of RLS. We therefore examined a line of Btbd9 mutant mice we recently generated for phenotypes similar to symptoms found in RLS patients. We observed that the Btbd9 mutant mice had motor restlessness, sensory alterations likely limited to the rest phase, and decreased sleep and increased wake times during the rest phase. Additionally, the Btbd9 mutant mice had altered serum iron levels and monoamine neurotransmitter systems. Furthermore, the sensory alterations in the Btbd9 mutant mice were relieved using ropinirole, a dopaminergic agonist widely used for RLS treatment. These results, taken together, suggest that the Btbd9 mutant mice model several characteristics similar to RLS and would therefore be the first genotypic mouse model of RLS. Furthermore, our data provide further evidence that BTBD9 is involved in RLS, and future studies of the Btbd9 mutant mice will help shine light on its role in the pathophysiology of RLS. Finally, our data argue for the utility of Btbd9 mutant mice to discover and screen novel therapeutics for RLS.

Laser heat stimulation of tiny skin areas adds valuable information to quantitative sensory testing in postherpetic neuralgia

Patients suffering from postherpetic neuralgia often complain about hypo- or hypersensation in the affected dermatome. The loss of thermal sensitivity has been demonstrated by quantitative sensory testing as being associated with small-fiber (Aδ- and C-fiber) deafferentation. We aimed to compare laser stimulation (radiant heat) to thermode stimulation (contact heat) with regard to their sensitivity and specificity to detect thermal sensory deficits related to small-fiber dysfunction in postherpetic neuralgia. We contrasted detection rate of laser stimuli with 5 thermal parameters (thresholds of cold/warm detection, cold/heat pain, and sensory limen) of quantitative sensory testing. Sixteen patients diagnosed with unilateral postherpetic neuralgia and 16 age- and gender-matched healthy control subjects were tested. Quantitative sensory testing and laser stimulation of tiny skin areas were performed in the neuralgia-affected skin and in the contralateral homologue of the neuralgia-free body side. Across the 5 thermal parameters of thermode stimulation, only one parameter (warm detection threshold) revealed sensory abnormalities (thermal hypoesthesia to warm stimuli) in the neuralgia-affected skin area of patients but not in the contralateral area, as compared to the control group. In contrast, patients perceived significantly less laser stimuli both in the affected skin and in the contralateral skin compared to controls. Overall, laser stimulation proved more sensitive and specific in detecting thermal sensory abnormalities in the neuralgia-affected skin, as well as in the control skin, than any single thermal parameter of thermode stimulation. Thus, laser stimulation of tiny skin areas might be a useful diagnostic tool for small-fiber dysfunction.

Restless legs and substantia nigra hypoechogenicity are common features in Friedreich's ataxia

Friedreich's ataxia (FA) is a multisystemic degenerative disease, but the prevalence of restless legs syndrome (RLS) is unknown. FA patients might be particularly susceptible to develop RLS as FA presents with features commonly associated with RLS, e.g. multisystemic network dysfunction, peripheral neuropathy and disturbances in subcellular brain iron homeostasis. In this work, we assessed the following: (1) the prevalence of RLS; (2) the prevalence of sonographic hypoechogenicity of the substantia nigra (SN), which is known to be associated with idiopathic RLS; and (3) the relation between both in 28 FA patients. Thirty-two percent of the patients suffered from RLS, thus clearly exceeding the prevalence rate in the general population. SN hypoechogenicity was more frequent in FA patients (61%) compared to healthy controls (7%) and was significantly associated with RLS. However, as SN echogenicity also correlated inversely with disease severity, it seems to be related not only to RLS, but also to the neurodegenerative process in FA itself. The high prevalence of RLS in FA patients warrants specific assessment by neurologists involved in the care of FA patients as treatments are readily available. Similar to patients with idiopathic RLS, reduced SN echogenicity is a frequent finding in FA, possibly indicating regional changes in subcellular brain iron regulation in FA.

Alterations in pain responses in treated and untreated patients with restless legs syndrome: associations with sleep disruption

OBJECTIVE

There has been recent interest in characterizing potential abnormalities of pain processing in patients with sleep disorders such as Restless Legs Syndrome (RLS). The aim of this study was to evaluate psychophysical responses to noxious heat and pressure stimuli in both treated and untreated RLS patients, compared to matched controls.

METHODS

This study is a cross-sectional group comparison of RLS patients with matched controls. A total of 31 patients (15 treated, 16 untreated) with a confirmed diagnosis of RLS were compared to 18 controls with no history of RLS or related sleep disorders.

RESULTS

RLS patients (both treated and untreated) demonstrated reduced pain thresholds and reported greater clinical pain relative to controls. Moreover, RLS patients demonstrated enhanced temporal summation of heat pain (p<.05), which may reflect aberrant central nervous system facilitation of pain transmission. Both treated and untreated RLS patients reported disrupted sleep relative to controls, and mediation analyses suggested that the reduced pain thresholds in RLS were attributable to sleep disturbance. However, the effect of RLS on the magnitude of temporal summation of heat pain was independent of sleep disturbance.

CONCLUSIONS

These findings suggest that central nervous system pain processing may be amplified in RLS, perhaps partially as a consequence of sleep disruption. RLS patients, even those whose symptoms are managed pharmacologically, may be at elevated long-term risk for the development or maintenance of persistent pain conditions. Further studies in larger samples could help to improve the prospects for pain management in RLS patients.

The role of quantitative sensory testing in the evaluation of musculoskeletal pain conditions

Quantitative sensory testing (QST) is a noninvasive method of assessing sensory and pain perception that has been used in the past 30 years primarily for analysis of cutaneous and mucosal perception. In recent years, several published studies have demonstrated that QST may be useful in the analysis of painful musculoskeletal disorders as well. Based on the results of these studies, it can be postulated that QST may be useful in the analysis of the pathogenesis, classification, and differential diagnosis of musculoskeletal disorders. However, due to the diverse ethiopathogenetic basis of these disorders, a broad range of QST test batteries may be necessary to analyze the various musculoskeletal disease entities. This review analyzes published studies on this subject and summarizes current information on altered sensory and pain perception available for some of the most common musculoskeletal disorders. At present, QST remains primarily a research tool but may be useful in differential diagnosis in indicating the presence of central sensitization and for clinical monitoring of disease progression or treatment response.