Non-obese lipedema patients show a distinctly altered quantitative sensory testing profile with high diagnostic potential

Introduction and Objectives

Lipedema is a widespread severe chronic disease affecting mostly women. Characterized by painful bilateral fat accumulation in extremities sparing hands and feet, objective measurement-based diagnosis is currently missing. We tested for characteristic psychometric and/or sensory alterations including pain and for their potential for medical routine diagnosis.

Methods

Pain psychometry was assessed using the German Pain Questionnaire. Sensory sensitivity toward painful and nonpainful stimuli was characterized in non-obese lipedema patients and matched controls using the validated quantitative sensory testing (QST) protocol of the German Research Network on Neuropathic Pain.

Results

Lipedema patients showed no overt psychometric abnormalities. Pain was reported as somatic rather than psychosomatic aversive. All QST measurements were normal, but the z-score of pressure pain thresholds (PPT) was twofold reduced and the z-score of vibration detection thresholds (VDT) was two and a half times increased. Both thresholds were selectively altered at the affected thigh but not the unaffected hand. Receiver operating characteristic analysis of the combination of PPT and VDT of thigh vs hand into a PVTH score (PPT, VDT, thigh, hand-score) shows high sensitivity and specificity, categorizing correctly 95.8% of the participants as lipedema patients or healthy controls. Bayesian inference analysis corroborated the diagnostic potential of such a combined PVTH score.

Conclusion

We propose to assess PPT and VDT at the painful thigh and the pain-free hand. Combination in a PVTH score may allow a convenient lipedema diagnosis early during disease development.

Fibromyalgia is associated with hypersensitivity but not with abnormal pain modulation: evidence from QST trials and spinal fMRI

Widespread pain and hyperalgesia are characteristics of chronic musculoskeletal pain conditions, including fibromyalgia syndrome (FM). Despite mixed evidence, there is increasing consensus that these characteristics depend on abnormal pain augmentation and dysfunctional pain inhibition. Our recent investigations of pain modulation with individually adjusted nociceptive stimuli have confirmed the mechanical and thermal hyperalgesia of FM patients but failed to detect abnormalities of pain summation or descending pain inhibition. Furthermore, our functional magnetic resonance imaging evaluations of spinal and brainstem pain processing during application of sensitivity-adjusted heat stimuli demonstrated similar temporal patterns of spinal cord activation in FM and HC participants. However, detailed modeling of brainstem activation showed that BOLD activity during "pain summation" was increased in FM subjects, suggesting differences in brain stem modulation of nociceptive stimuli compared to HC. Whereas these differences in brain stem activation are likely related to the hypersensitivity of FM patients, the overall central pain modulation of FM showed no significant abnormalities. These findings suggest that FM patients are hyperalgesic but modulate nociceptive input as effectively as HC.

Beyond biopsychosocial: The keystone mechanism theory of pain

Pain is a deeply personal experience, with interindividual differences in its chronification and treatment presenting a formidable healthcare challenge. The biopsychosocial model (BPSm) has been hugely influential within nascent attempts at precision pain medicine, steering the field away from a reductionist biomechanical viewpoint and emphasising complex interactions of biological, psychological, and social factors which shape the individuality of pain. However, despite offering a strong theoretical foundation and holistic perspective, we contend that the BPSm remains limited in its capacity to deliver truly mechanistically informed treatment of pain. We therefore propose the keystone model of pain which offers a pragmatic balance between the dimensionality expansive BPSm and overly reductive approaches, providing both theoretical and practical advantages for the transition from treating populations to individual people.

The potential effect of walking on quantitative sensory testing, pain catastrophizing, and perceived stress: an exploratory study

OBJECTIVES

Studies suggest that a range of pain mechanisms, such as poor quality of sleep, perceived stress, pain catastrophizing or pain sensitivity, are likely to enhance clinical pain. Animal studies suggest that these pain mechanisms can be modulated by increasing physical activity, but human data are needed to support this hypothesis. This exploratory study aimed to investigate the changes in pain mechanisms after a simple self-directed walking program of 8-weeks. Additionally, this exploratory study investigated the interaction between changes over time in assessments of poor quality of sleep, perceived stress, pain catastrophizing or pain sensitivity and how these changes interacted with each other.

METHODS

This prospective cohort study included 30 healthy subjects who were assessed at baseline and 4- and 8-weeks after initiating the walking program (30 min walking/day for 8 weeks). Self-report outcomes included: Pain Catastrophizing Scale (PCS), the Perceived Stress Scale (PSS) and Pittsburgh Sleep Quality Index. Pressure pain thresholds, temporal summation of pain and conditioned pain modulation (CPM) were assessed using cuff algometry.

RESULTS

Twenty-four subjects completed all the visits (age: 42.2, SD: 14.9, 16 females). PCS and PSS significantly decreased at the 8-week's visit compared to baseline (p<0.05). No significant differences were seen for an improvement in quality of sleep (p=0.071) and pain sensitivity (p>0.075) when comparing the 8-week's visit to the baseline visit. Changes in pain mechanisms comparing baseline and 8-weeks data were calculated and regression analyses found that an improvement in PCS was associated with an improvement in CPM (R2=0.197, p=0.017) and that a higher adherence to the walking program was associated with a larger improvement in PCS (R2=0.216, p=0.013).

CONCLUSIONS

The current exploratory study indicates that a simple self-directed walking program of 8-weeks can improve pain catastrophizing thoughts, perceived stress. Higher adherence to the walking program were associated with an improvement in pain catastrophizing and an improvement in pain catastrophizing was associated with an increase in conditioned pain modulation.

Pure small fiber neuropathy in alcohol dependency detected by skin biopsy

BACKGROUND

Alcohol overconsumption is well known to cause damage to the peripheral nervous system. The aim of this study was the functional and structural evaluation of the small nerve fibers in alcohol-dependent subjects, with or without symptoms of peripheral neuropathy.

METHODS

Twenty-six consecutive alcohol-dependent subjects treated for detoxification voluntarily in the specialized unit of the Athens University Psychiatric Clinic were enrolled in this prospective study over 18 months. Every subject was assessed by peripheral nerve evaluation using the Neuropathy Symptoms Score (NSS) and Neuropathy Impairment Score (NIS), followed by nerve conduction studies (NCS), quantitative sensory testing (QST), and skin biopsy. Twenty-nine normal subjects, age- and gender-matched, constituted the control group.

RESULTS

Peripheral neuropathy was diagnosed in 16 subjects (61.5%). Among these 16 subjects, pure large fiber neuropathy (LFN) was found in two subjects (12.5%), pure small fiber neuropathy (SFN) was found in eight subjects (50%), and both large and small fiber neuropathy was diagnosed in six patients (37.5%). The intraepidermal nerve fiber density (IENFD) of the patients' skin biopsy was significantly lower than that of the control group. Additionally, QST results showed a statistically significant sensory impairment in the patients.

CONCLUSIONS

Our study confirms small fiber neuropathy due to alcohol abuse with a high prevalence of pure SFN that might have remained undetected without QST and IENFD.

Current Evidence for Biological Biomarkers and Mechanisms Underlying Acute to Chronic Pain Transition across the Pediatric Age Spectrum

Chronic pain is highly prevalent in the pediatric population. Many factors are involved in the transition from acute to chronic pain. Currently, there are conceptual models proposed, but they lack a mechanistically sound integrated theory considering the stages of child development. Objective biomarkers are critically needed for the diagnosis, risk stratification, and prognosis of the pathological stages of pain chronification. In this article, we summarize the current evidence on mechanisms and biomarkers of acute to chronic pain transitions in infants and children through the developmental lens. The goal is to identify gaps and outline future directions for basic and clinical research toward a developmentally informed theory of pain chronification in the pediatric population. At the outset, the importance of objective biomarkers for chronification of pain in children is outlined, followed by a summary of the current evidence on the mechanisms of acute to chronic pain transition in adults, in order to contrast with the developmental mechanisms of pain chronification in the pediatric population. Evidence is presented to show that chronic pain may have its origin from insults early in life, which prime the child for the development of chronic pain in later life. Furthermore, available genetic, epigenetic, psychophysical, electrophysiological, neuroimaging, neuroimmune, and sex mechanisms are described in infants and older children. In conclusion, future directions are discussed with a focus on research gaps, translational and clinical implications. Utilization of developmental mechanisms framework to inform clinical decision-making and strategies for prevention and management of acute to chronic pain transitions in children, is highlighted.

Prospective orofacial quantitative sensory testing data of the human face and mouth

Quantitative sensory testing (QST) is a valuable tool in the assessment of orofacial somatosensory function and dysfunction. QST is a method where thermal and mechanical stimuli are applied to the area of interest in a noninvasive way. The QST technique can detect patterns of loss of sensation that may happen in case of hypoesthesia, hypoalgesia, anesthesia, or gain of sensation in the context of allodynia, hyperalgesia or spontaneous pain. Normal values have already been recorded for some parts of the face and mouth, but not for the complete innervation area of the trigeminal nerve. This dataset involves orofacial QST gathered from ten healthy volunteers, a standardized QST battery was applied to 24 regions (14 extraoral and 10 intraoral) innervated by the trigeminal nerve. Descriptive statistics were applied to compare the different regions. This dataset can be used to inform future studies involving orofacial sensory function, pain studies and pharmacological trials.

Functional and morphometric assessment of small-fibre damage in late-onset hereditary transthyretin amyloidosis with polyneuropathy: the controversial relation between small-fibre-related symptoms and diagnostic test findings

INTRODUCTION

We aimed at investigating whether functional and morphometric tests assessing small-fibre damage, ie quantitative sensory testing, Sudoscan and skin biopsy, reliably reflect neuropathic pain and autonomic symptoms in patients with late-onset hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN).

METHODS

In 30 patients with late-onset ATTRv-PN, we collected quantitative sensory testing, Sudoscan and skin biopsy with assessment of intraepidermal, piloerector muscle and sweat gland nerve fibre density. We then correlated these functional and morphometric parameters with neuropathic pain and autonomic symptoms as assessed with the Neuropathic Pain Symptom Inventory (NPSI) and Composite Autonomic Symptom Score-31 (COMPASS-31).

RESULTS

50% of patients showed small-fibre damage in the form of a pure small-fibre neuropathy, 47% in the context of a mixed fibre neuropathy with small and large fibre involvement. All patients complained of at least one autonomic symptom and 60% had neuropathic pain. Whereas quantitative sensory testing and Sudoscan parameters correlated with neuropathic pain and autonomic symptoms as assessed by NPSI and COMPASS-31, intraepidermal, piloerector muscle and sweat gland nerve fibre density quantification did not.

CONCLUSIONS

Our findings indicate that functional test parameters reliably reflect neuropathic pain and autonomic symptoms related to small-fibre damage. These findings might help to identify clinically useful biomarkers to assess patient follow-up.

Post-Traumatic Trigeminal Neuropathic Pain after Dental Implant Surgery and the Injustice Experience Questionnaire

Painful post-traumatic trigeminal neuropathy (PTTN) is a known complication of dental implant therapy. Patients with PTTN develop sensory abnormalities in the orofacial region, which may be a psychosocial aspect, and dentists should assess somatosensory testing and psychosocial factors. The patients were assessed using quantitative sensory testing (QST). A 64-year-old female presented with allodynia of the left lower lip that occurred after a surgical implant procedure. Persistent pain started 4 months after the placement of two dental implants in the mandible. Sensory testing of these areas revealed warm hyposensitivity and mechanical hypersensitivity of the mandibular region. We also assessed PTTN-related perceived injustice using the Injustice Experience Questionnaire. The patient refused medication therapy such as pregabalin; therefore, autogenic training was adopted as an alternative management strategy. We conclude that for expensive dental procedures, such as implant placement, sufficient consensus should be obtained preoperatively before proceeding with surgery.

Quantitative sensory testing: a good tool to identify subclinical neuropathy in ATTRV30M amyloidosis patients?

BACKGROUND

Quantitative sensory testing (QST) has been one of the neurophysiological tools used for follow-up and disease progression assessment in ATTRv amyloidosis. We aimed to detect the utility of QST in identifying subclinical neuropathic involvement in ATTRV30M amyloidosis carriers.

METHODS

A cohort of ATTRV30M amyloidosis carriers were assessed with vibratory (VDT) and cooling (CDT) detection thresholds and heat pain responses. Subjects were divided into asymptomatic carriers (Group 1), paucisymptomatic carriers (Group 2) and stage 1 ATTRv-PN patients (Group 3). Nonparametric statistics were used for group comparisons.

RESULTS

A total of 207 ATTRV30M amyloidosis carriers (83 males) were included. Of these, 113 subjects were asymptomatic and 94 symptomatic carriers. In asymptomatic carriers, CDT and Heat Pain (HP 5.0 and HP 0.5) were significantly lower when compared to both group of symptomatic carriers (p ≤ 0.005). In Group 3, VDT, CDT and HP 5.0 were significantly higher, when compared to Group 2 (p < 0.05).

CONCLUSIONS

QST, in particular CDT, HP 5 and HP 0.5 modalities, seems a good tool to identify subclinical neuropathy in ATTRv amyloidosis carriers, with CDT showing a higher sensitivity to detect and early neuropathic involvement.

Sensory testing might not be perfect - but it is the best biomarker for pain phenotypes we have right now

Currently available treatments for neuropathic pain fail in roughly half of the patients - and it is impossible to predict which treatments will help patients. Stratification of neuropathic pain patients is needed, and sensory profiling has so far been the most promising approach: it has been shown to be responsive to treatment, linked to potential mechanisms, and, most importantly, predictive of treatment success. Despite a number of limitations, it is the currently most promising stratification tool and should be refined rather than disregarded.

Neuromodulation of somatosensory pain thresholds of the neck musculature using a novel transcranial direct current stimulation montage: a randomized double-blind, sham controlled study

OBJECTIVES

Anodal transcranial direct current stimulation (tDCS) of primary motor cortex (M1) and cathodal of the primary sensory cortex (S1) have previously shown to modulate the sensory thresholds when administered with the reference electrode located over the contralateral supraorbital area (SO). Combining the two stimulation paradigms into one with simultaneous stimulation of the two brain areas (M1 + S1 - tDCS) may result in a synergistic effect inducing a prominent neuromodulation, noticeable in the pain thresholds. The aim of this study is to assess the efficacy of the novel M1 + S1 - tDCS montage compared to sham-stimulation in modulating the pain thresholds in healthy adults.

METHODS

Thirty-nine (20 males) subjects were randomly assigned to either receiving 20 min. active M1 + S1 - tDCS or sham tDCS in a double-blinded single session study. Thermal and mechanical pain thresholds were assessed before and after the intervention.

RESULTS

There were no significant differences in the pain thresholds within either group, or between the M1 + S1 - tDCS group and the Sham-tDCS group (p>0.05), indicating that the intervention was ineffective in inducing a neuromodulation of the somatosensory system.

CONCLUSIONS

Experimental investigations of novel tDCS electrode montages, that are scientifically based on existing studies or computational modelling, are essential to establish better tDCS protocols. Here simultaneous transcranial direct current stimulation of the primary motor cortex and primary sensory cortex showed no effect on the pain thresholds of the neck musculature in healthy subjects. This tDCS montage may have been ineffective due to how the electrical field reaches the targeted neurons, or may have been limited by the design of a single tDCS administration. The study adds to the existing literature of the studies investigating effects of new tDCS montages with the aim of establishing novel non-invasive brain stimulation interventions for chronic neck pain rehabilitation. North Denmark Region Committee on Health Research Ethics (VN-20180085) ClinicalTrials.gov (NCT04658485).

AMAZONE: prevention of persistent pain after breast cancer treatment by online cognitive behavioral therapy-study protocol of a randomized controlled multicenter trial

Background

Surviving breast cancer does not necessarily mean complete recovery to a premorbid state of health. Among the multiple psychological and somatic symptoms that reduce the quality of life of breast cancer survivors, persistent pain after breast cancer treatment (PPBCT) with a prevalence of 15–65% is probably the most invalidating. Once chronic, PPBCT is difficult to treat and requires an individualized multidisciplinary approach. In the past decades, several somatic and psychological risk factors for PPBCT have been identified. Studies aiming to prevent PPBCT by reducing perioperative pain intensity have not yet shown a significant reduction of PPBCT prevalence. Only few studies have been performed to modify psychological distress around breast cancer surgery. The AMAZONE study aims to investigate the effect of online cognitive behavioral therapy (e-CBT) on the prevalence of PPBCT.

Methods

The AMAZONE study is a multicenter randomized controlled trial, with an additional control arm. Patients (n=138) scheduled for unilateral breast cancer surgery scoring high for surgical or cancer-related fears, general anxiety or pain catastrophizing are randomized to receive either five sessions of e-CBT or online education consisting of information about surgery and a healthy lifestyle (EDU). The first session is scheduled before surgery. In addition to the online sessions, patients have three online appointments with a psychotherapist. Patients with low anxiety or catastrophizing scores (n=322) receive treatment as usual (TAU, additional control arm).

Primary endpoint is PPBCT prevalence 6 months after surgery.

Secondary endpoints are PPBCT intensity, the intensity of acute postoperative pain during the first week after surgery, cessation of postoperative opioid use, PPBCT prevalence at 12 months, pain interference, the sensitivity of the nociceptive and non-nociceptive somatosensory system as measured by quantitative sensory testing (QST), the efficiency of endogenous pain modulation assessed by conditioned pain modulation (CPM) and quality of life, anxiety, depression, catastrophizing, and fear of recurrence until 12 months post-surgery.

Discussion

With perioperative e-CBT targeting preoperative anxiety and pain catastrophizing, we expect to reduce the prevalence and intensity of PPBCT. By means of QST and CPM, we aim to unravel underlying pathophysiological mechanisms. The online application facilitates accessibility and feasibility in a for breast cancer patients emotionally and physically burdened time period.

Trial registration

NTR NL9132, registered December 16 2020.

The Population Structure of a Globe Artichoke Worldwide Collection, as Revealed by Molecular and Phenotypic Analyzes

The knowledge of the organization of the domesticated gene pool of crop species is an essential requirement to understand crop evolution, to rationalize conservation programs, and to support practical decisions in plant breeding. Here, we integrate simple sequence repeat (SSR) analysis and phenotypic characterization to investigate a globe artichoke collection that comprises most of the varieties cultivated worldwide. We show that the cultivated gene pool of globe artichoke includes five distinct genetic groups associated with the major phenotypic typologies: Catanesi (which based on our analysis corresponds to Violetti di Provenza), Spinosi, Violetti di Toscana, Romaneschi, and Macau. We observed that 17 and 11% of the molecular and phenotypic variance, respectively, is between these groups, while within groups, strong linkage disequilibrium and heterozygote excess are evident. The divergence between groups for quantitative traits correlates with the average broad-sense heritability within the groups. The phenotypic divergence between groups for both qualitative and quantitative traits is strongly and positively correlated with SSR divergence (F_ST) between groups. All this implies a low population size and strong bottleneck effects, and indicates a long history of clonal propagation and selection during the evolution of the domesticated gene pool of globe artichoke. Moreover, the comparison between molecular and phenotypic population structures suggests that harvest time, plant architecture (i.e., plant height, stem length), leaf spininess, head morphology (i.e., head shape, bract shape, spininess) together with the number of heads per plant were the main targets of selection during the evolution of the cultivated germplasm. We emphasize our findings in light of the potential exploitation of this collection for association mapping studies.

Can Intra-Oral Qualitative Sensory Testing Foretell Postoperative Dental Pain? A Preliminary Report

Pain prevention and management is one of the primary goals of dental care. Postoperative dental pain (PDP) following caries removal and performance of a restorative dental treatment is a common clinical phenomenon, often causing significant discomfort to dental patients. In the present study, a psychophysical non-invasive method, qualitative sensory testing (QualST), was used in an attempt to foretell PDP following dental restorative procedures. Forty-two dental patients underwent an intra-oral cold QualST four times: immediately prior to a restorative dental procedure and at a follow-up meeting 1−3 weeks later, on the treated and on the contralateral oral sides. The QualST measures included subjects’ evaluation of the magnitude of pain and cold sensations experienced (on visual analogue scales) and the duration of the cold sensation (in seconds). Additional measures included age, gender, level of dental anxiety, jaw treated, and type of dental restoration performed (Class I or Class V). Subjects’ PDP was assessed through the phone using numeric rating scales 24, 48, and 72 h postoperatively. The highest level of PDP experienced by subjects occurred 24 h postoperatively (ANOVA with repeated measures). Of the study variables, the QualST pain sensation (B = 0.645, p < 0.001), duration of the cold sensation (B = 0.042, p < 0.05), and an interaction between gender and dental anxiety (B = 0.136, p < 0.05) emerged as possible predictors of the highest PDP experienced by subjects (stepwise regression). The results suggest that subjects’ reaction to an intra-oral cold stimulation of the oral mucosa can serve as a potential tool to foretell postoperative dental pain following restorative dental procedures.

After-Sensations and Lingering Pain following Examination in Patients with Fibromyalgia Syndrome

Fibromyalgia syndrome (FMS) is a chronic widespread pain condition with mixed peripheral and central contributions. Patients display hypersensitivities to a spectrum of stimuli. Patients' blunt pressure pain thresholds are typically reduced, and sometimes (∼15%) gentle brushstroke induces allodynia. However, after-sensations following these stimuli have not, to our knowledge, been reported. We examined the perception of blunt pressure and 'pleasant touch' in FMS. Patients were first interviewed and completed standard psychometric questionnaires. We then measured their sensitivity to blunt pressure and perception of pleasant touch including after-sensations; patients were followed for five days evaluating lingering pain from blunt pressure. We recruited 51 FMS patients and 16 pain-free controls (HC) at a UK Pain Management Centre. Forty-four patients completed the after-sensation protocol. Most patients reported pain after application of less mechanical pressure than HCs; median arm and leg thresholds were 167 kPa and 233 kPa. Eighty-four percent (31/37) of patients reported ongoing pain at the site of pressure application one day after testing, and 49% (18/37) still perceived pain at five days. After-sensations following brushstroke were common in the FMS group, reported by 77% (34/44) compared to 25% (4/16) of HCs; 34% (15/44) patients, but no HCs, perceived these after-sensations as uncomfortable. For FMS patients who experienced after-sensations, brushstroke-pleasantness ratings were reduced, and skin was often an important site of pain. Pain after blunt pressure assessment typically lingers for several days. After-sensations following brushstroke stimulation is a previously unreported FMS phenomenon. They are associated with tactile anhedonia and may identify a clinically distinct subgroup.

Unique features of central neuropathic pain in multiple sclerosis: Results of a cluster analysis

Background

Central neuropathic pain (CNP) is an excruciating condition, prevalent in up to a third of patients with multiple sclerosis (MS). Identifying CNP among MS patients is particularly challenging considering the ample comorbid chronic pain conditions and sensory disturbances entailed by the disease. The aim was to identify sensory features unique to CNP beyond those of chronic pain and MS.

Methods

Participants were 112 MS patients: 44 with a diagnosis of CNP, 28 with a diagnosis of chronic musculoskeletal pain (MSP), and 40 pain free. Participants underwent testing of thermal and mechanical thresholds, thermal grill illusion (TGI), pain adaptation (PA), and offset analgesia (OA), and chronic pain was characterized. A two‐step cluster analysis was performed, and the association between the cluster membership and the clinical group membership (CNP, MSP, pain free) was evaluated.

Results

The CNP and MSP groups were similar in most of the chronic pain variables (e.g., severity, location and quality) and MS‐related variables (e.g., type, severity and medication intake). The three created clusters had unique sensory features: (1) ‘Hyposensitivity’ (increased thermal and touch thresholds) characterized the CNP group; (2) ‘Poor inhibition and hyperalgesia’ (worst PA and OA and decreased TGI threshold) characterized the MSP group; and (3) ‘Efficient inhibition’ (best PA and OA, smallest sensory loss) characterized the pain‐free group.

Conclusions

The unique sensory features of CNP and MSP provide insight into their pathophysiology, and evaluating them may increase the ability to provide individually based interventions. Efficient inhibition may protect MS patients from chronic pain.

Significance

Cluster analysis among patients with multiple sclerosis (MS) revealed that while central neuropathic pain is associated with thermal and mechanical hypoesthesia, musculoskeletal pain is involved with reduced pain inhibition and hyperalgesia; sensory profiles that provide insights into the mechanisms of these conditions and may promote an individually based pain management.

Cerebral Perfusion and Sensory Testing Results Differ in Interstitial Cystitis/Bladder Pain Syndrome Patients with and without Fibromyalgia: A Site-Specific MAPP Network Study

Purpose

Fibromyalgia is a common co-morbidity in patients with interstitial cystitis/bladder pain syndrome. Quantitative sensory testing measures and regional cerebral blood flow measures have been noted to differ from healthy controls in both subjects with fibromyalgia and those with interstitial cystitis when studied independently. The present study examined such measures in subjects with the diagnosis of interstitial cystitis both with and without the co-diagnosis of fibromyalgia to determine whether differences in these measures may be associated with co-morbidity.

Patients and Methods

Female subjects with the diagnosis of interstitial cystitis with (n = 15) and without (n = 19) the co-diagnosis of fibromyalgia as well as healthy control subjects (n = 41) underwent quantitative sensory testing. A subset of these patients (9 with and 9 without fibromyalgia) underwent brain perfusion studies using arterial spin labeled functional magnetic resonance imaging. An analysis was performed of absolute regional cerebral blood flow of regions-of-interest when experiencing a full bladder compared with an empty bladder.

Results

Subjects with both interstitial cystitis and fibromyalgia were more hypersensitive than those without fibromyalgia as well as healthy controls in most sensory measures except heat. Subjects with interstitial cystitis, but no fibromyalgia, differed from healthy controls only in toleration of the ischemic forearm task. Other co-morbidities were more common in those subjects with both interstitial cystitis and fibromyalgia. Bladder fullness was associated with significantly greater whole brain gray matter blood flow in subjects with interstitial cystitis and fibromyalgia when compared with that of subjects with interstitial cystitis without fibromyalgia. Examination of regional cerebral blood flow in individual regions-of-interest demonstrated statistically significant differences between the subjects with interstitial cystitis with and those without fibromyalgia bilaterally in the thalamus, amygdala and hippocampus, as well as the right prefrontal cortex and greater responsiveness to changes in bladder fullness in the insula.

Conclusion

Quantitative sensory testing and brain perfusion data support that there are two phenotypes of interstitial cystitis patients, which can be differentiated by a co-diagnosis of fibromyalgia. This may affect responsiveness to treatment and suggest the utility of stratifying interstitial cystitis patients according to their co-morbidities.

The Definition, Assessment, and Prevalence of (Human Assumed) Central Sensitisation in Patients with Chronic Low Back Pain: A Systematic Review

Central sensitisation is assumed to be one of the underlying mechanisms for chronic low back pain. Because central sensitisation is not directly assessable in humans, the term 'human assumed central sensitisation' (HACS) is suggested. The objectives were to investigate what definitions for HACS have been used, to evaluate the methods to assess HACS, to assess the validity of those methods, and to estimate the prevalence of HACS. Database search resulted in 34 included studies. Forty different definition references were used to define HACS. This review uncovered twenty quantitative methods to assess HACS, including four questionnaires and sixteen quantitative sensory testing measures. The prevalence of HACS in patients with chronic low back pain was estimated in three studies. The current systematic review highlights that multiple definitions, assessment methods, and prevalence estimates are stated in the literature regarding HACS in patients with chronic low back pain. Most of the assessment methods of HACS are not validated but have been tested for reliability and repeatability. Given the lack of a gold standard to assess HACS, an initial grading system is proposed to standardize clinical and research assessments of HACS in patients with a chronic low back.

Development of GaN HEMTs Fabricated on Silicon, Silicon-on-Insulator, and Engineered Substrates and the Heterogeneous Integration

GaN HEMT has attracted a lot of attention in recent years owing to its wide applications from the high-frequency power amplifier to the high voltage devices used in power electronic systems. Development of GaN HEMT on Si-based substrate is currently the main focus of the industry to reduce the cost as well as to integrate GaN with Si-based components. However, the direct growth of GaN on Si has the challenge of high defect density that compromises the performance, reliability, and yield. Defects are typically nucleated at the GaN/Si heterointerface due to both lattice and thermal mismatches between GaN and Si. In this article, we will review the current status of GaN on Si in terms of epitaxy and device performances in high frequency and high-power applications. Recently, different substrate structures including silicon-on-insulator (SOI) and engineered poly-AlN (QST^®) are introduced to enhance the epitaxy quality by reducing the mismatches. We will discuss the development and potential benefit of these novel substrates. Moreover, SOI may provide a path to enable the integration of GaN with Si CMOS. Finally, the recent development of 3D hetero-integration technology to combine GaN technology and CMOS is also illustrated.

Sensory Function and Psychological Factors in Children With Complex Regional Pain Syndrome Type 1

OBJECTIVE

To assess thermal-sensory thresholds and psychosocial factors in children with Complex Regional Pain Syndrome Type 1 (CRPS-I) compared to healthy children.

METHODS

We conducted quantitative sensory testing on 34 children with CRPS-I and 56 pain-free children. Warm, cool, heat, and cold stimuli were applied to the forearm. Children with CRPS-I had the protocol administered to the pain site and the contralateral-pain site. Participants completed the self-report Behavior Assessment System for Children.

RESULTS

Longer pain durations (>5.1 months) were associated with decreased sensitivity to cold pain on the pain site (P = .04). Higher pain-intensity ratings were associated with elevated anxiety scores (P = .03). Anxiety and social stress were associated with warmth sensitivity (both P < .05) on the contralateral-pain site.

CONCLUSIONS

Pain duration is an important factor in assessing pediatric CRPS-I. Hyposensitivity in the affected limb may emerge due to degeneration of nociceptive nerves. Anxiety may contribute to thermal-sensory perception in childhood CRPS-I.

Changes in pain profile of patients with haemophilia during 1-year follow-up

INTRODUCTION

Patients with haemophilia (PwH) may experience increased sensitivity to pain. Based on the assessment of the somatosensory system, a recent study showed a specific pain profile in PwH when compared to controls by using Quantitative Sensory Testing (QST).

AIM

This study aimed to evaluate the pain profile of affected joints (knee or ankle joints) and a non-affected site (dominant hand) in adult PwH over a 1-year period.

METHODS

Twenty-four PwH (severe haemophilia A = 19, B = 3; moderate haemophilia A = 1, B = 1; age: 52±8 years) and 21 healthy controls (age: 52±12 years) were examined by QST. Both knee or ankle joints and the hand as reference were examined twice with an interval of 1 year in order to assess several detection (DT) and pain thresholds (PT).

RESULTS

Statistically significant altered mechanical (P < .001) and pressure (P < .05) PT were found at affected joints and at a non-affected site in PwH when compared to controls. Mechanical DT showed a significant increase at all assessed sites (e.g., at ankle joints PwH vs. controls at baseline/follow up in mN: 13.9±9.8 vs. 12.0±8.2/19.4±12.4 vs. 13.7±11.1; P < .01) in both cohorts. Nevertheless, changes in most parameters within 1 year occurred similarly in both groups.

CONCLUSION

The statistically significant different QST profile between PwH and controls does not seem to deteriorate further over the course of the year. Thus, under prophylactic treatment, the existing difference in the pain profile between PwH and controls at baseline does not appear to be a progressive process within 1 year.

Low mechano-afferent fibers reduce thermal pain but not pain intensity in CRPS

Background

Human hairy (not glabrous skin) is equipped with a subgroup of C-fibers, the C-tactile (CT) fibers. Those do not mediate pain but affective aspects of touch. CT-fiber-activation reduces experimental pain if they are intact. In this pilot study we investigated pain modulating capacities of CT-afferents in CRPS.

Methods

10 CRPS-patients (mean age 33 years, SEM 3.3) and 11 healthy controls (mean age 43.2 years, SEM 3.9) participated.

CT-targeted-touch (brush stroking, velocity: 3 cm/s) was applied on hairy and glabrous skin on the affected and contralateral limb. Patients rated pleasantness of CT-targeted-touch (anchors: 1 “not pleasant”—4 “very pleasant”) twice daily on 10 days. Pain intensity (NRS: 0 “no pain” – 10 “worst pain imaginable”) was assessed before, 0, 30, 60 and 120 min after each CT-stimulation. To assess sensory changes, quantitative-sensory-testing was performed at the beginning and the end of the trial period.

Results

CT-targeted-touch was felt more pleasant on the healthy compared to the affected limb on hairy (p < 0.001) and glabrous skin (p 0.002), independent of allodynia. In contrast to healthy controls patients felt no difference between stimulating glabrous and hairy skin on the affected limb. Thermal pain thresholds increased after CT-stimulation on the affected limb (cold-pain-threshold: p 0.016; heat-pain-threshold: p 0.033).

Conclusions

CT-stimulation normalizes thermal pain thresholds but has no effect on the overall pain in CRPS. Therefore, pain modulating properties of CT-fibers might be too weak to alter chronic pain in CRPS. Moreover, CT-fibers appear to lose their ability to mediate pleasant aspects of touch in CRPS.

Opioid Specific Effects on Central Processing of Sensation and Pain: A Randomized, Cross-Over, Placebo-Controlled Study

Moderate to severe pain is often treated with opioids, but central mechanisms underlying opioid analgesia are poorly understood. Findings thus far have been contradictory and none could infer opioid specific effects. This placebo-controlled, randomized, 2-way cross-over, double-blinded study aimed to explore opioid specific effects on central processing of external stimuli. Twenty healthy male volunteers were included and 3 sets of assessments were done at each of the 2 visits: 1) baseline, 2) during continuous morphine or placebo intravenous infusion and 3) during simultaneous morphine + naloxone or placebo infusion. Opioid antagonist naloxone was introduced in order to investigate opioid specific effects by observing which morphine effects are reversed by this intervention. Quantitative sensory testing, spinal nociceptive withdrawal reflexes (NWR), spinal electroencephalography (EEG), cortical EEG responses to external stimuli and resting EEG were measured and analyzed. Longer lasting pain (cold-pressor test - hand in 2° water for 2 minutes, tetanic electrical), deeper structure pain (bone pressure) and strong nociceptive (NWR) stimulations were the most sensitive quantitative sensory testing measures of opioid analgesia. In line with this, the principal opioid specific central changes were seen in NWRs, EEG responses to NWRs and cold-pressor EEG. The magnitude of NWRs together with amplitudes and insular source strengths of the corresponding EEG responses were attenuated. The decreases in EEG activity were correlated to subjective unpleasantness scores. Brain activity underlying slow cold-pressor EEG (1-4Hz) was decreased, whereas the brain activity underlying faster EEG (8-12Hz) was increased. These changes were strongly correlated to subjective pain relief. This study points to evidence of opioid specific effects on perception of external stimuli and the underlying central responses. The analgesic response to opioids is likely a synergy of opioids acting at both spinal and supra-spinal levels of the central nervous system. Due to the strong correlations with pain relief, the changes in EEG signals during cold-pressor test have the potential to serve as biomarkers of opioid analgesia. PERSPECTIVE: This exploratory study presents evidence of opioid specific effects on the pain system at peripheral and central levels. The findings give insights into which measures are the most sensitive for assessing opioid-specific effects.

Skin biopsy and quantitative sensory assessment in an Italian cohort of ATTRv patients with polyneuropathy and asymptomatic carriers: possible evidence of early non-length dependent denervation

AIM

Study of intraepidermal nerve fiber density (IENFD) by skin biopsy represents a promising tool in the evaluation of patients with ATTRv polyneuropathy (ATTRv-PN). Herein, we retrospectively analyze intraepidermal innervation and quantitative sensory test (QST) data from an Italian cohort of Italian ATTRv-PN patients and asymptomatic carriers aimed to provide insights into early nerve pathological and functional changes in this disease.

METHODS

IENFD and QST data of 14 ATTRv-PN patients and 14 asymptomatic carriers were retrospectively analyzed together with clinical and paraclinical data such as disease stage and severity, neuropathic pain scales, and sural SNAP amplitude.

RESULTS

Given an estimated time to the predicted age of onset of symptomatic disease of 20.27 + / - 7.9 years, small nerve fiber loss seems to be unexpectedly early in carriers. Moreover, carriers showed skin denervation at the proximal (thigh) site, suggesting a non-length-dependent neuropathic process. IENFD at ankle correlated with disease severity and other paraclinical variables such as sural nerve potential amplitude and QST parameters. Patients at earlier stages of the disease did not show significant differences in ankle IENFD compared with asymptomatic carriers, but significant differences in terms of QST parameters, small fiber neuropathy symptoms, and neuropathic pain.

CONCLUSIONS

Skin biopsy can disclose an early non-length-dependent small fiber loss in ATTRv-PN and, together with QST, could provide a useful insight disease onset and progression.

Pain Study in X-Linked Adrenoleukodystrophy in Males and Females

INTRODUCTION

X-linked adrenoleukodystrophy (ALD) is a metabolic disorder in which very long chain fatty acids (VLCFAs) are accumulated in the nervous system and adrenal cortex, impairing their functions. Three main variants are described in males: adrenomyeloneuropathy (AMN), a cerebral form (cALD or cAMN) and Addison's disease only (AD), while for females no classification is used. To evaluate pain and the functional state of afferent fibers, a series of tests was carried out in male and female patients.

METHODS

Chronic pain occurrence and sensory phenotype profile were assessed in 30 patients (20 male: 10 AMN, 1 cAMN, 1 cALD, 8 AD; and 10 female). A set of instruments assessed the intensity, quality and extent of pain, while a battery of quantitative sensory testing (QST) procedures examined the functional status of Aβ and Aδ fibers. Principal component analysis and hierarchical clustering with sensory responses input were used to identify distinct clusters.

RESULTS

Nearly half of the subjects reported pain, with a high prevalence in females and male AMN patients. No sex differences in pain dimensions were found. The sensory responses were heterogeneous, differing among the clinical variants and between genders. Male AMN/cAMN/cALD patients showed the worst impairment. Aβ and Aδ fibers were affected in males and females, but Aβ fibers appeared undamaged in females when tactile sensitivity was tested. Abnormal responses were localized in the lower body district, according to the dying-back pattern of the neuropathy. Cluster analysis showed discrete clusters for each function examined, with well-interpretable sensory and clinical phenotypes.

CONCLUSION

The study of pain and of the sensory profile appears to indicate a difference in the mechanisms underlying the AMN/cAMN/cALD and AD clinical forms and in the treatment of the respective generated pain types.

The Short-Term Kinetics of sICAM-1 after Induction of Acute Experimental Pain in Healthy Volunteers

Intercellular adhesion molecule-1 (ICAM-1) mediates extravasation of leukocytes, releasing proinflammatory cytokines or endogenous opioids in the inflamed tissue. Thus, ICAM-1 is a crucial component of peripheral antinociception. Previously, we demonstrated a significant correlation between the soluble form of ICAM (sICAM-1) in serum and pain intensity reported by chronic pain patients. The present study examines the role and kinetics of sICAM-1 in experimentally induced acute pain. Three groups of 10 subjects were exposed to 10 min of high (capsaicin-enhanced) or low-intensity heat pain or cold pain, respectively. Thermal stimuli were induced using a device for quantitative sensory testing. Topical capsaicin significantly increased heat pain intensity without the risk of thermal tissue damage. Pain intensity was recorded every minute during testing. sICAM-1 concentrations in serum were determined by ELISA before, immediately after, and 60 min after test termination. Among all experimental groups, sICAM-1 significantly decreased immediately after pain induction. After 60 min, sICAM-1 concentrations returned towards initial values. Interestingly, a linear correlation was found between the extent of sICAM-1 changes and the initial concentrations. Whereas high initial values led to a distinct decrease of sICAM-1, low concentrations tended to increase. There was no statistically significant correlation between levels or alterations of serum sICAM-1 and pain intensity reported by the test subjects. In contrast to our previous findings in chronic pain patients, the present results show that sICAM-1 values do not correlate with the intensity of acute experimental pain. However, we were able to detect short-term changes of sICAM-1 after induction of nociceptive thermal stimuli, suggesting that this marker is part of a demand-oriented homeostatically controlled system.

Pain perception and processing in individuals with posttraumatic stress disorder: a systematic review with meta-analysis

Supplemental Digital Content is Available in the Text.

Posttraumatic stress disorder encompasses latent subgroups of individuals with qualitative differences in pain perception.

Posttraumatic stress disorder (PTSD) is a known risk factor for the development of chronic pain conditions, and almost 1 in 5 individuals with chronic pain fulfills the criteria for PTSD. However, the relationship between PTSD and pain is poorly understood and studies on pain perception in patients with PTSD show inconsistent results suggesting that different sensory profiles exist among individuals with PTSD. Here, we (1) systematically summarize the current literature on experimentally evoked pain perception in patients with PTSD compared to subjects without PTSD, and (2) assess whether the nature of the traumatic event is associated with different patterns in pain perception. The main outcome measures were pain threshold, pain tolerance, and pain intensity ratings as well as measures of temporal summation of pain and conditioned pain modulation. A systematic search of MEDLINE, EMBASE, Web of Science, PsycINFO, and CINAHL identified 21 studies for the meta-analysis, including 422 individuals with PTSD and 496 PTSD-free controls. No main effect of PTSD on any outcome measure was found. However, stratification according to the nature of trauma revealed significant differences of small to medium effect sizes. Combat-related PTSD was associated with increased pain thresholds, whereas accident-related PTSD was associated with decreased pain thresholds. No clear relationship between PTSD and experimentally evoked pain perception exists. The type of trauma may affect pain thresholds differently indicating the presence of different subgroups with qualitative differences in pain processing.

Gold Standard for Diagnosis of DPN

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes mellitus. It often causes symmetrical paresthesia, loss of sensation, and hyperalgesia. Without early intervention, it might lead to diabetic foot ulceration, gangrene, and subsequent amputation in people with diabetes. DPN is an insidious disease and often underdiagnosed. This paper reviews the current national and international prevalence of DPN, screening methods for early DPN, including quantitative sensory measurement, neurological function scoring system, confocal microscopy, and high-frequency ultrasound, and summarizes the related research progress, clinical application, and development prospects of these methods in recent years.

Chronic Pain Diagnosis Using Machine Learning, Questionnaires, and QST: A Sensitivity Experiment

In the last decade, machine learning has been widely used in different fields, especially because of its capacity to work with complex data. With the support of machine learning techniques, different studies have been using data-driven approaches to better understand some syndromes like mild cognitive impairment, Alzheimer’s disease, schizophrenia, and chronic pain. Chronic pain is a complex disease that can recurrently be misdiagnosed due to its comorbidities with other syndromes with which it shares symptoms. Within that context, several studies have been suggesting different machine learning algorithms to classify or predict chronic pain conditions. Those algorithms were fed with a diversity of data types, from self-report data based on questionnaires to the most advanced brain imaging techniques. In this study, we assessed the sensitivity of different algorithms and datasets classifying chronic pain syndromes. Together with this assessment, we highlighted important methodological steps that should be taken into account when an experiment using machine learning is conducted. The best results were obtained by ensemble-based algorithms and the dataset containing the greatest diversity of information, resulting in area under the receiver operating curve (AUC) values of around 0.85. In addition, the performance of the algorithms is strongly related to the hyper-parameters. Thus, a good strategy for hyper-parameter optimization should be used to extract the most from the algorithm. These findings support the notion that machine learning can be a powerful tool to better understand chronic pain conditions.

Profiling thermal pain using quantitative sensory testing in patients with trigeminal nerve injury

OBJECTIVES

To investigate the thermal pain phenotypes using QST in patients with unilateral trigeminal nerve injury and to explore whether these different thermal pain phenotypes are associated with clinical and psychophysical characteristics.

METHODS

This retrospective study included 84 patients diagnosed with posttraumatic trigeminal neuropathy involving inferior alveolar nerve (IAN) and lingual nerve (LN). Data on clinical characteristics, subjective symptoms including hypoesthesia, dysesthesia, and allodynia, and objective signs using thermal QST were collected and explored.

RESULTS

Three heat (heat hypoalgesia, heat hyperalgesia, and within normal range) and cold pain phenotypes (cold hypoalgesia, cold hyperalgesia, and within normal ranges) were identified, respectively. Thermal hypoalgesia was more frequently observed than thermal hyperalgesia. Heat hypoalgesia regardless of cold pain abnormalities appears to be associated with subjective negative symptoms, while thermal hyperalgesia seems to have little relationship with negative and positive symptoms. Thermal pain phenotypes were associated with loss of innocuous thermal sensation. Unlike heat pain phenotypes, cold pain phenotypes differed between IAN injury and LN injury.

CONCLUSION

The thermal pain phenotypes identified in this study seem to be related to clinical and psychophysical findings differently. These results would be a good starting point for assessing posttraumatic trigeminal neuropathy and interpreting the thermal QST results.

Bridging the Gap Between Vessels and Nerves in Fabry Disease

Purpose

Fabry disease frequently includes pain as an early disease feature, which was characterized as a dysfunctional processing of somatosensory information in various studies. The pathomechanism involves the mutation in the x-chromosomal GLA-gene and a consequent reduction of the α-galactosidase. This results in an insufficient reduction of globotriaosylceramide (GL3). Interestingly, an accumulation of GL3 was shown in both vascular endothelial cells and nerve tissue. This implicates that both an endothelial and nerve-dependent dysfunction may be considered as prominent mechanisms in pain pathogeneses.

Patients and Methods

The exploration of endothelial and C-fiber-dependent microcirculatory changes was conducted in a healthy cohort (n = 22) and in patients with polyneuropathy (n = 21) and Fabry disease (n = 15). Microcirculatory measurements were conducted using a laser speckle contrast analysis (LASCA) in combination with a thermoprobe controlling system, which applied a constant heat stimulus (42°C). Additionally, nerve fiber function was assessed via Quantitative Sensory Testing and heart rate variability (HRV).

Results

The results indicated a characteristic perfusion profile in the control group as well as both patient groups. Fabry patients had the smallest increase of endothelial-dependent perfusion as compared to the others [% increase as compared to Fabry: control + 129% (p = 0.002), PNP + 126% (p = 0.019)]. The sensory testing indicated a dysfunctional processing of A-delta fibers in Fabry disease as compared to healthy controls [cold detection threshold (CDT): p = 0.004, mechanical pain threshold (MPT): p = 0.007] and PNP patients (MPT: p = 0.001).

Conclusion

Our results point to both an endothelial and a nerve-dependent dysfunction in Fabry disease. Therefore, not only direct changes in nerve fiber tissue may contribute to an altered sensory processing. Indeed, evidence of a perfusion change in vasa nervorum could also contribute to the dysfunctional processing of sensory information, which likely occurs under physical stress.

Follow-up in transthyretin familial amyloid polyneuropathy: Useful investigations

Patients with transthyretin amyloid polyneuropathy (TTR-FAP) and asymptomatic mutation-carriers have to be regularly followed-up in order to identify disease progression and the time point for starting or modifying therapy. In this case series we describe the potential suitability of different variables as progression markers. We retrospectively analyzed the follow-up charts of 10 TTR-FAP patients. Clinical examination included the Neuropathy Impairment Score of Lower Limb (NIS-LL), temperature perception thresholds, nerve conduction and autonomic function tests. The NIS-LL had the greatest value for a sensitive and correct follow-up for all TTR-FAP stages. All other examinations provided useful additional information but they were either less suited for advanced TTR-FAP, or had a higher test-retest variability. The results of this study provide preliminary evidence that a good clinical investigation is mandatory in TTR-FAP follow-up. Simple neuropathy scores like the NIS-LL might be as useful as technical investigations for TTR-FAP follow-up.

Thermal sensitivity in humans at the depth of thermal receptor endings beneath the skin: validation of a heat transfer model of the skin using high-temporal resolution stimuli

PURPOSE

The bioheat transfer equation predicts temperature distribution in living tissues such as the skin. This study aimed at psychophysically validating this model in humans.

METHODS

Three experiments were performed. In the first, participants were asked to judge the thermal intensity of stimuli with combinations of intensity and duration that yielded, according to the model, identical temperatures at the thermoreceptor's depth. In experiment 2, participants' thermal detection thresholds for stimuli of different durations were measured to verify whether these thresholds correspond, according to the model, to equivalent temperatures at the thermoreceptor's location. In experiment 3, an alternative forced choice method was used, in which subjects indicated which of the two consecutive thermal stimulations was more intense.

RESULTS

The model predicted results that agreed with subjects' perceptions. Participants judged stimuli of different combinations of intensities and durations yielding identical temperature at the receptor level as having equivalent intensity. Moreover, although cold detection thresholds for stimuli of different durations differed for temperatures of the stimulating probe, stimulations using the model's parameters showed equivalence at the depth of the thermal receptors. Furthermore, stimuli with temperature/duration combinations for which the model predicts temperature equivalence at the depth of the receptors corresponded to subjective equalization.

CONCLUSION

These findings indicate that heat transfer models provide good estimates of temperatures at the thermal receptors. Use of these models may facilitate comparisons among studies using different stimulation devices and may facilitate the establishment of standards involving all stimulation parameters.

Quantitative Sensory Testing (QST) in Drug-Naïve Patients with Parkinson's Disease

BACKGROUND

Pain is highly prevalent in patients with Parkinson's disease (PD), but underlying pathophysiological mechanisms are largely unclear. Alterations in somatosensory processing might contribute to sensory abnormalities in PD.

OBJECTIVE

This study investigated sensory processing in PD patients.

METHODS

We used the standardized "Quantitative Sensory Testing" (QST) protocol (German Research Network on Neuropathic Pain) to investigate 13 somatosensory parameters in 19 PD patients naïve to dopaminergic medication and 19 healthy controls matched for age, gender, and handedness. We tested for differences in sensory parameters between i) drug-naïve PD patients and healthy controls, ii) patients' more and less affected body side, and iii) for an association of somatosensory parameters with disease-specific factors.

RESULTS

We did not observe any significant group differences in somatosensory parameters between PD patients and healthy subjects. In PD patients, QST mean z-scores did not differ between the predominantly and the less affected body side, PD patients with and without PD-specific chronic pain or between different PD subtypes. Age, but not PD disease severity, was associated with a greater loss of function in thermal and mechanical detection thresholds.

CONCLUSIONS

Somatosensory processing, as assessed with the well-established QST protocol, was normal in drug-naïve PD patients. Thus, somatosensory abnormalities previously reported in medicated PD patients might rather be a result of dopaminergic medication, or may occur later in the course of the disease or with increasing age.

Quantitative Systems Toxicology Approaches to Understand and Predict Drug-Induced Liver Injury

The DILI-sim Initiative is a public-private partnership using quantitative systems toxicology to build a model (DILIsym) capable of understanding and predicting liver safety liabilities in drug candidates. The effort has provided insights into mechanisms underlying dose-dependent drug-induced liver injury (DILI) and interpatient differences in susceptibility to dose-dependent DILI. DILIsym may be useful in identifying drugs capable of causing idiosyncratic hepatotoxicity. DILIsym is used to optimize interpretation of traditional and newer serum biomarkers of DILI. DILIsym results are considered in drug development decisions. In the future, it may be possible to use DILsym predictions to justify reduction in size of some clinical trials.

Quantitative systems toxicology (QST) reproduces species differences in PF-04895162 liver safety due to combined mitochondrial and bile acid toxicity

Many compounds that appear promising in preclinical species, fail in human clinical trials due to safety concerns. The FDA has strongly encouraged the application of modeling in drug development to improve product safety. This study illustrates how DILIsym, a computational representation of liver injury, was able to reproduce species differences in liver toxicity due to PF-04895162 (ICA-105665). PF-04895162, a drug in development for the treatment of epilepsy, was terminated after transaminase elevations were observed in healthy volunteers (NCT01691274). Liver safety concerns had not been raised in preclinical safety studies. DILIsym, which integrates in vitro data on mechanisms of hepatotoxicity with predicted in vivo liver exposure, reproduced clinical hepatotoxicity and the absence of hepatotoxicity observed in the rat. Simulated differences were multifactorial. Simulated liver exposure was greater in humans than rats. The simulated human hepatotoxicity was demonstrated to be due to the interaction between mitochondrial toxicity and bile acid transporter inhibition; elimination of either mechanism from the simulations abrogated injury. The bile acid contribution occurred despite the fact that the IC50 for bile salt export pump (BSEP) inhibition by PF-04895162 was higher (311 µmol/L) than that has been generally thought to contribute to hepatotoxicity. Modeling even higher PF-04895162 liver exposures than were measured in the rat safety studies aggravated mitochondrial toxicity but did not result in rat hepatotoxicity due to insufficient accumulation of cytotoxic bile acid species. This investigative study highlights the potential for combined in vitro and computational screening methods to identify latent hepatotoxic risks and paves the way for similar and prospective studies.

Association between quantitative sensory testing and pain or disability in paediatric chronic pain: protocol for a systematic review and meta-analysis

INTRODUCTION

This protocol describes the objective and methods of a systematic review of the association between quantitative sensory testing (QST) measures and pain intensity or disability in paediatric chronic pain (PCP). The review will also assess whether the relationship strength is moderated by variables related to the QST method and pain condition; the use of QST in PCP (modalities, outcome measures and anatomical test sites as well as differentiating between pain mechanisms (eg, neuropathic vs nociceptive) and in selecting analgesics); the reliability of QST across the paediatric age range; the ability of QST to differentiate patients with chronic pain from healthy controls; and differences between anatomical test sites.

METHODS AND ANALYSIS

Medline, PsycINFO, CINHAL, Web of Science, Scopus, Cochrane Library and OpenGrey will be searched. English language studies will be eligible if they recruit a sample aged 6-24 (inclusive) with chronic pain, including primary and secondary pain; apply at least one of the following QST modalities: chemical, electrical, mechanical (subgroups include pressure, punctate/brush and vibratory) or thermal stimulus to measure perception of noxious or innocuous stimuli applied to skin, muscle or joint; use a testing protocol to control for stimulus properties: modality, anatomical site, intensity, duration and sequence. Following title and abstract screening, the full texts of relevant records will be independently assessed by two reviewers. For eligible studies, one reviewer will extract study characteristics and data, and another will check for accuracy. Both will undertake independent quality assessments using the Appraisal Tool for Cross-Sectional Studies. A qualitative synthesis will be presented with discussion centred around different QST modalities. Where eligible data permit, meta-analyses will be performed separately for different QST modalities using comprehensive meta-analysis.

ETHICS AND DISSEMINATION

Review findings will be reported in a peer-reviewed journal and presented at conferences. The study raises no ethical issues.

PROSPERO REGISTRATION NUMBER

CRD42019134069.

Keys to Recruiting and Retaining Seriously Ill African Americans With Sickle Cell Disease in Longitudinal Studies: Respectful Engagement and Persistence

OBJECTIVES

Sickle cell disease (SCD) is a serious illness with disabling acute and chronic pain that needs better therapies, but insufficient patient participation in research is a major impediment to advancing SCD pain management. The purpose of this article is to discuss the challenges of conducting an SCD study and approaches to successfully overcoming those challenges.

DESIGN

In a repeated-measures, longitudinal study designed to characterize SCD pain phenotypes, we recruited 311 adults of African ancestry. Adults with SCD completed 4 study visits 6 months apart, and age- and gender-matched healthy controls completed 1 visit.

RESULTS

We recruited and completed measures on 186 patients with SCD and 125 healthy controls. We retained 151 patients with SCD with data at 4 time points over 18 months and 125 healthy controls (1 time point) but encountered many challenges in recruitment and study visit completion. Enrollment delays often arose from patients' difficulty in taking time from their complicated lives and frequent pain episodes. Once scheduled, participants with SCD cancelled 49% of visits often because of pain; controls canceled 30% of their scheduled visits. To facilitate recruitment and retention, we implemented a number of strategies that were invaluable in our success.

CONCLUSION

Patients' struggles with illness, chronic pain, and their life situations resulted in many challenges to recruitment and completion of study visits. Important to overcoming challenges was gaining the trust of patients with SCD and a participant-centered approach. Early identification of potential problems allowed strategies to be instituted proactively, leading to success.

Thermal and mechanical quantitative sensory testing values among healthy African American adults

PURPOSE

Only a few studies have reported quantitative sensory testing (QST) reference values for healthy African Americans, and those studies are limited in sample size and age of participants. The study purpose was to characterize QST values in healthy, pain-free African American adults and older adults whose prior pain experiences and psychological status were also measured. We examined the QST values for differences by sex, age, and body test site.

PATIENTS AND METHODS

A cross-sectional sample of 124 pain-free African American adults (age 18-69 years, 49% female) completed demographic and self-reported pain, fatigue and psychosocial measures. QST was performed to obtain thermal and mechanical responses and associated pain intensity levels.

RESULTS

We found thermal detection values at the anterior forearm were (29.2 °C±1.6) for cool detection (CD) and (34.5 °C±1.2) for warm detection (WD). At that site the sample had cold pain threshold (CPTh) (26.3 °C±5.0), heat pain threshold (HPTh) (37.8 °C±3.6), and mechanical pain thresholds (MPTH) (16.7±22.2 grams of force, gF). There was a significant between sex difference for WD, with women being more sensitive (q=0.027). Lower body sites were less sensitive than upper body sites across all thermal modalities (q<0.003), but not for the mechanical modality.

CONCLUSION

The QST values from this protocol at the anterior forearm indicate that the healthy African American adults had average thermal pain thresholds close to the temperature of adaptation and average MPTh under 20 gF. Differences in responses to thermal and mechanical stimuli for upper verses lower body were consistent with prior research.

An experimental investigation of the relationships among race, prayer, and pain

Background and aims Compared to White individuals, Black individuals demonstrate a lower pain tolerance. Research suggests that differences in pain coping strategies, such as prayer, may mediate this race difference. However, previous research has been cross-sectional and has not determined whether prayer in and of itself or rather the passive nature of prayer is driving the effects on pain tolerance. The aim of this study was to clarify the relationships among race, prayer (both active and passive), and pain tolerance. Methods We randomly assigned 208 pain-free participants (47% Black, 53% White) to one of three groups: active prayer ("God, help me endure the pain"), passive prayer ("God, take the pain away"), or no prayer ("The sky is blue"). Participants first completed a series of questionnaires including the Duke University Religion Index, the Coping Strategies Questionnaire-Revised (CSQ-R), and the Pain Catastrophizing Scale. Participants were then instructed to repeat a specified prayer or distractor coping statement while undergoing a cold pressor task. Cold pain tolerance was measured by the number of seconds that had elapsed while the participant's hand remained in the cold water bath (maximum 180 s). Results Results of independent samples t-tests indicated that Black participants scored higher on the CSQ-R prayer/hoping subscale. However, there were no race differences among other coping strategies, religiosity, or catastrophizing. Results of a 2 (Race: White vs. Black)×3 (Prayer: active vs. passive vs. no prayer) ANCOVA controlling for a general tendency to pray and catastrophizing in response to prayer indicated a main effect of prayer that approached significance (p=0.06). Pairwise comparisons indicated that those in the active prayer condition demonstrated greater pain tolerance than those in the passive (p=0.06) and no prayer (p=0.03) conditions. Those in the passive and no prayer distractor conditions did not significantly differ (p=0.70). There was also a trending main effect of race [p=0.08], with White participants demonstrating greater pain tolerance than Black participants. Conclusions Taken together, these results indicate that Black participants demonstrated a lower pain tolerance than White participants, and those in the active prayer condition demonstrated greater tolerance than those in the passive and no prayer conditions. Furthermore, Black participants in the passive prayer group demonstrated the lowest pain tolerance, while White participants in the active prayer group exhibited the greatest tolerance. Results of this study suggest that passive prayer, like other passive coping strategies, may be related to lower pain tolerance and thus poorer pain outcomes, perhaps especially for Black individuals. On the other hand, results suggest active prayer is associated with greater pain tolerance, especially for White individuals. Implications These results suggest that understanding the influence of prayer on pain may require differentiation between active versus passive prayer strategies. Like other active coping strategies for pain, active prayer may facilitate self-management of pain and thus enhance pain outcomes independent of race. Psychosocial interventions may help religiously-oriented individuals, regardless of race, cultivate a more active style of prayer to improve their quality of life.

Potential biomarkers for persistent and neuropathic pain therapy

Persistent, in particular neuropathic pain affects millions of people worldwide. However, the response rate of patients to existing analgesic drugs is less than 50%. There are several possibilities to increase this response rate, such as optimization of the pharmacokinetic and pharmacodynamic properties of analgesics. Another promising approach is to use prognostic biomarkers in patients to determine the optimal pharmacological therapy for each individual. Here, we discuss recent efforts to identify plasma and CSF biomarkers, as well as genetic biomarkers and sensory testing, and how these readouts could be exploited for the prediction of a suitable pharmacological treatment. Collectively, the information on single biomarkers may be stored in knowledge bases and processed by machine-learning and related artificial intelligence techniques, resulting in the optimal pharmacological treatment for individual pain patients. We highlight the potential for biomarker-based individualized pain therapies and discuss biomarker reliability and their utility in clinical practice, as well as limitations of this approach.

Outcome of a High-Frequency Transcutaneous Electrical Nerve Stimulator (hfTENS) Device for Low Back Pain: A Randomized Controlled Trial

OBJECTIVE

This controlled trial examined the benefit of a high-frequency transcutaneous electrical nerve stimulation (hfTENS) device (the Quell, NeuroMetrix, Inc., Waltham, MA, U.S.A.) for patients with chronic low back pain (CLBP).

METHODS

Thirty-five (n = 35) participants were randomly assigned to use the device each day for 3 months (experimental group) and were compared with 33 subjects without the device (treatment-as-usual control group). All patients were instructed to complete baseline questionnaires and were assessed on thresholds of pressure pain and mechanical temporal summation as part of standardized quantitative sensory testing (QST). The subjects also uploaded smartphone applications (apps) for tracking use of the hfTENS and for daily pain assessment. Each participant completed weekly phone interviews, was prompted to complete daily pain app assessments, and was asked to repeat the baseline questionnaires again after 6 weeks and 3 months.

RESULTS

Sixty percent of the subjects were female, 77.9% were Caucasian, and the average age was 46.2 years. Significant reductions in pain intensity (P < 0.01) and activity interference (P < 0.025) and significant improvements in pain catastrophizing (P < 0.025) were noted in the experimental group compared with the control group. No group differences were found on depression, anxiety, or pain-related disability. Older subjects with a longer duration of pain tended to use the hfTENS more often. Subjects who showed greater sensitivity based on QST results revealed increased use of the hfTENS (P < 0.025) and tended to believe that the hfTENS was more helpful in reducing their back pain, but these findings did not reach significance (P = 0.09).

CONCLUSION

These results suggest that hfTENS can have a moderate effect in reducing pain and improving quality of life in low back pain patients. Further trials designed to determine the mechanism of action of the hfTENS are needed.

Vibrotactile sensitivity of patients with HIV-related sensory neuropathy: An exploratory study

BACKGROUND

HIV-associated distal polyneuropathy (HIV-PN) affects large and small sensory nerve fibers and can cause tactile insensitivity. This exploratory study forms part of an effort to apply subsensory electrical nerve stimulation (SENS) to improve tactile sensitivity of patients with HIV-PN. This work presented an opportunity to use a robust protocol to quantitatively describe the vibrotactile sensitivity of individuals with HIV-PN on effective antiretroviral therapy (ART) and correlate these findings with commonly used clinical vibration testing and scoring grades.

METHODS

The vibration perception thresholds (VPTs) of 20 patients with HIV-PN at three vibration frequencies (25, 50, and 128 Hz) were measured. We compare the vibration perception threshold (VPT) outcomes to an age- and gender-matched control cohort. We further correlated VPT findings with 128 Hz tuning fork (TF) assessments performed on the HIV-PN participants, accrued as part of a larger study. HIV-PN was defined as having at least one distal symmetrical neuropathic sign, although 18 of 20 had at least two neuropathic signs.

CONCLUSIONS

HIV-PN participants were found to have lower VPT sensitivity than controls for all three vibration frequencies, and VPT was more sensitive at higher vibration frequencies for both HIV-PN and controls. VPT sensitivity was reduced with older age. Years on ART was correlated with VPT-25 Hz but not with VPT in general. Notably, VPT sensitivity did not correlate with the clinically used 128 Hz TF severity grades. Outcomes of tests for interaction with vibration frequency suggest that HIV-PN pathology does not affect all mechanoreceptors similarly.

Dynamic of the somatosensory system in postherpetic neuralgia

Introduction:

In postherpetic neuralgia (PHN) different types of patients can be distinguished regarding their predominant peripheral nociceptor function.

Objective:

The aim was to examine somatosensory profiles in the course of disease with special regard to the different subtypes existing in PHN.

Methods:

Twenty patients with PHN (7 men and 13 women, age 67 ± 9.6 years) were examined at baseline (disease duration 18.1 ± 26 months) and follow-up (31.6 ± 23.8 months later) with quantitative sensory testing (protocol of the German Research Network on Neuropathic Pain).

Results:

Fourteen (70%) PHN patients presented with impaired (iPHN) and 6 (30%) with preserved (pPHN) C-fiber function. Groups did not differ regarding age, disease duration, or pain intensity at baseline. Both groups did not differ regarding change in pain intensity (−0.5 ± 2.3 vs −1.7 ± 2.6 numerical rating scale, P = n.s.) at follow-up. Impaired PHN improved in thermal and mechanical detection thresholds as well as allodynia independent from change in pain intensity. By contrast, pPHN showed an increase in mechanical pain sensitivity (1.4 ± 2.5 vs −0.4 ± 2.2, P < 0.05) and a trend towards a stronger loss of detection (66% vs 33%, P = n.s.) on follow-up.

Conclusion:

Results demonstrate that patients with preserved C-fiber function are more predisposed to develop signs of central sensitization as demonstrated by an increased mechanical pain sensitivity. Impaired C-fiber function is able to improve even in chronic cases, but a functional loss is unlikely to play a role here. The knowledge of development of somatosensory profiles in the course of the disease offers possibilities to optimize a mechanism-based treatment.

Insights About the Neuroplasticity State on the Effect of Intramuscular Electrical Stimulation in Pain and Disability Associated With Chronic Myofascial Pain Syndrome (MPS): A Double-Blind, Randomized, Sham-Controlled Trial

Background: There is limited evidence concerning the effect of intramuscular electrical stimulation (EIMS) on the neural mechanisms of pain and disability associated with chronic Myofascial Pain Syndrome (MPS). Objectives: To provide new insights into the EIMS long-term effect on pain and disability related to chronic MPS (primary outcomes). To assess if the neuroplasticity state at baseline could predict the long-term impact of EIMS on disability due to MPS we examined the relationship between the serum brain-derived-neurotrophic-factor (BDNF) and by motor evoked potential (MEP). Also, we evaluated if the EIMS could improve the descending pain modulatory system (DPMS) and the cortical excitability measured by transcranial magnetic stimulation (TMS) parameters. Methods: We included 24 right-handed female with chronic MPS, 19-65 years old. They were randomically allocated to receive ten sessions of EIMS, 2 Hz at the cervical paraspinal region or a sham intervention (n = 12). Results: A mixed model analysis of variance revealed that EIMS decreased daily pain scores by -73.02% [95% confidence interval (CI) = -95.28 to -52.30] and disability due to pain -43.19 (95%CI, -57.23 to -29.39) at 3 months of follow up. The relative risk for using analgesics was 2.95 (95% CI, 1.36 to 6.30) in the sham group. In the EIMS and sham, the change on the Numerical Pain Scale (NPS0-10) throughout CPM-task was -2.04 (0.79) vs. -0.94 (1.18), respectively, (P = 0.01). EIMS reduced the MEP -28.79 (-53.44 to -4.15), while improved DPMS and intracortical inhibition. The MEP amplitude before treatment [(Beta = -0.61, (-0.58 to -0.26)] and a more significant change from pre- to post-treatment on serum BDNF) (Beta = 0.67; CI95% = 0.07 to 1.26) were predictors to EIMS effect on pain and disability due to pain. Conclusion: These findings suggest that a bottom-up effect induced by the EIMS reduced the analgesic use, improved pain, and disability due to chronic MPS. This effect might be mediated by an enhancing of corticospinal inhibition as seen by an increase in IC and a decrease in MEP amplitude. Likewise, the MEP amplitude before treatment and the changes induced by the EIMS in the serum BDNF predicted it's long-term clinical impact on pain and disability due MPS. The trial is recorded in ClinicalTrials.gov: NCT02381171.

Is quantitative sensory testing helpful in the management of oxaliplatin neuropathy? a two-year clinical study

PURPOSE

To better understand how quantitative sensory testing could help the clinician in the management of oxaliplatin-induced peripheral neuropathy in terms of earlier and more reliable detection, we conducted a two-year prospective study.

METHODS

Thermal sensory assessment, tactile sensory assessment, neuropathic pain assessment and adverse events gradation (NCI-CTC) were performed during treatment and 6 months after treatment completion.

RESULTS

35 patients were enrolled and followed-up during one year. Cold and Warm Detection Thresholds were higher 6 months after treatment completion than at enrollment. Mechanical detection thresholds didn't change significantly. Neurotoxicity was mostly grade-1, only 18% grade-2 and no grade-3. Grade-2 patients received lower oxaliplatin cumulative dose than grade-1, which reveals effective dose adaptation and grade-2 patients were more likely to develop painful neuropathy.

CONCLUSION

Thermal thresholds impairment emerges too late to help the clinician in the prophylaxis of neuropathy. Management of OXA-treatment based on NCI-CTC, as currently recommended, remains the best way to detect neuropathy and ensure treatment adaptation.

Local adaptation through genetic differentiation in highly fragmented Tilia cordata populations

We assessed the level of geographic differentiation of Tilia cordata in Denmark based on tests of 91 trees selected from 12 isolated populations. We used quantitative analysis of spring phenology and population genetic analysis based on SSR markers to infer the likely historical genetic processes within and among populations. High genetic variation within and among populations was observed in spring phenology, which correlated with spring temperatures at the origin of the tested T. cordata trees. The population genetic analysis revealed significant differentiation among the populations, but with no clear sign of isolation by distance. We infer the findings as indications of ongoing fine scale selection in favor of local growth conditions made possible by limited gene flow among the small and fragmented populations. This hypothesis fits well with reports of limited fruiting in the investigated Danish T. cordata populations, while the species is known for its ability to propagate vegetatively by root suckers. Our results suggest that both divergent selection and genetic drift may have played important roles in forming the genetic patterns of T. cordata at its northern distribution limit. However, we also speculate that epigenetic mechanism arising from the original population environment could have created similar patterns in regulating the spring phenology.

Quantitative Sensory Testing, Antihistamines, and Beta-Blockers for Management of Persistent Breast Pain: A Case Series

BACKGROUND

It is not uncommon for mothers to have persistent pain with breastfeeding beyond the first few weeks after birth. Persistent pain can be multifactorial, with neuropathic pain maintained by central sensitization being one dimension. Our knowledge in delineating categories of persistent pain is simple and not very sophisticated.

METHODS

We have developed and tested a Lactation Quantitative Sensory Test (L-QST) to quantify the neuropathic component of persistent breastfeeding pain. We present three case reports of neuropathic breastfeeding pain and treatment, and we discuss the potential role of histamine and catecholamines in persistent breastfeeding-associated pain.

CONCLUSIONS

The L-QST can be a useful tool to quantify neuropathic pain. Further studies are needed to test inter-observer reliability and reproducibility of this tool. Antihistamines can be considered for treating persistent pain in breastfeeding women with a history of allergy or atopy, and beta-blockers may be helpful in women with multiple pain disorders.

Up-Down Reader: An Open Source Program for Efficiently Processing 50% von Frey Thresholds

Most pathological pain conditions in patients and rodent pain models result in marked alterations in mechanosensation and the gold standard way to measure this is by use of von Frey fibers. These graded monofilaments are used to gauge the level of stimulus-evoked sensitivity present in the affected dermal region. One of the most popular methods used to determine von Frey thresholds is the up–down testing paradigm introduced by Dixon for patients in 1980 and by Chapman and colleagues for rodents in 1994. Although the up–down method is very accurate, leading to its widespread use, defining the 50% threshold from primary data is complex and requires a relatively time-consuming analysis step. We developed a computer program, the Up–Down Reader (UDReader), that can locate and recognize handwritten von Frey assessments from a scanned PDF document and translate these measurements into 50% pain thresholds. Automating the process of obtaining the 50% threshold values negates the need for reference tables or Microsoft Excel formulae and eliminates the chance of a manual calculation error. Our simple and straightforward method is designed to save research time while improving data collection accuracy and is freely available at https://sourceforge.net/projects/updownreader/ or in supplementary files attached to this manuscript.