Sensory and Thermal Quantitative Testing in Children With Sickle Cell Disease

Adverse childhood experiences, brain efficiency, and the development of pain symptoms in youth

BACKGROUND

Adverse childhood experiences (ACEs) are often reported by youths with chronic pain, and both ACEs and chronic pain disrupt how information is processed. However, it is unknown whether changes to shared neural networks underlie the relationship between ACEs and the development of pain symptoms. This study explored the relationships between ACEs, brain efficiency, and pain symptomology in youth.

METHODS

A community sample of youths aged 14-18 years underwent MRIs, answered trauma and pain questionnaires, and underwent pain sensory testing, twice, 3 months apart (Nbaseline = 44; Nfollow-up = 42). Sensory testing determined thresholds for mechanical and thermal stimuli. Global and local network efficiencies were evaluated using graph theory. Generalized estimating equations were applied to examine whether brain efficiency moderated the relationships between ACEs, pain intensity, and pain sensitivity (i.e., mechanical detection, heat pain, and temperature change thresholds).

RESULTS

There was a significant interaction between ACEs and global brain efficiency in association with pain intensity (β = -0.31, p = 0.02) and heat pain (β = -0.29, p = 0.004). Lower global brain efficiency exacerbated the relationship between ACEs and pain intensity (θX → Y|W = -1.16 = 0.37, p = 0.05), and heat pain sensitivity (θX → Y|W = -1.30 = 0.44, p = 0.05). Higher global brain efficiency ameliorated the relationship between ACEs and pain intensity (θX → Y|W = 1.75 = -0.53, p = 0.05).

CONCLUSIONS

The relationship between ACEs and pain symptomology was comparable to chronic pain phenotypes (i.e., higher pain intensity and pain thresholds) and may vary as a function of brain efficiency in youth. This stresses the importance of assessing for pain symptoms in trauma-exposed youth, as earlier identification and intervention are critical in preventing the chronification of pain.

SIGNIFICANCE

This article explores the relationship between ACEs, pain symptomology, and brain efficiency in youth. ACEs may affect how the brain processes information, including pain. Youths with lower brain efficiencies that were exposed to more ACEs have pain symptomology comparable to youths with chronic pain. Understanding this relationship is important for the earlier identification of pain symptoms, particularly in vulnerable populations such as youths exposed to trauma, and is critical for preventing the chronification of pain.

Altered pain processing and sensitization in sickle cell disease: a scoping review of quantitative sensory testing findings

OBJECTIVES

Over 50% of adults living with sickle cell disease (SCD) have chronic pain, but the underlying mechanisms of chronic pain in this population remain unclear. Quantitative sensory testing is an important measurement tool for understanding pain and sensory processing. This scoping review summarizes quantitative sensory testing methodologies used in sickle cell studies and the evidence for central sensitization in this population.

METHODS

We conducted a systematic search of PubMed, Embase, and CINAHL to identify studies using quantitative sensory testing in individuals living with sickle cell disease. Search strategies were based on variations of the terms "sickle cell disease," and "quantitative sensory testing." Eligible studies were observational or experimental studies in human participants living with SCD that reported findings and detailed methodology for at least 1 quantitative sensory testing modality.

RESULTS

Our search yielded a total of 274 records; 27 of which are included in this scoping review. Of the 27 studies, 17 were original studies (with combined total of 516 adult and 298 pediatric participants), and 10 were secondary or subgroup analyses of these prior studies. Significant variation existed in quantitative sensory testing methodologies across studies, including testing locations, type and intensity of stimuli, and interpretation of findings. Of the identified studies, 22% (2/9 studies) reported sensory abnormalities in mechanical sensitivity and thresholds, 22% (2/9 studies) reported abnormal pressure pain thresholds, 46% (6/13 studies) reported sensory abnormalities in thermal pain thresholds and tolerance (cold and warm), and 50% (2/4 studies) reported abnormalities in temporal summation.

CONCLUSION

Future studies should use standardized quantitative sensory testing protocols with consistent and operationalized definitions of sensitization to provide clear insight about pain processing and central sensitization in sickle cell disease.

Descending Facilitation of Nociceptive Transmission From the Rostral Ventromedial Medulla Contributes to Hyperalgesia in Mice with Sickle Cell Disease

Sickle cell disease (SCD) is an inherited blood disorder that is associated with acute episodic and chronic pain. Mice with SCD have robust hyperalgesia mediated, in part, by sensitization of spinal dorsal horn neurons. However, underlying mechanisms are not fully understood. Since the rostral ventromedial medulla (RVM) is a major component of descending circuitry that modulates nociceptive transmission in the spinal cord, we examined if the RVM contributes to hyperalgesia in mice with SCD. Injection of lidocaine, but not vehicle, into the RVM eliminated mechanical and heat hyperalgesia in sickle (HbSS-BERK) mice without altering mechanical and heat sensitivity in naïve C57B mice. These data indicate that the RVM contributes to the maintenance of hyperalgesia in mice with SCD. In electrophysiological studies, we determined the changes in response properties of RVM neurons that might contribute to hyperalgesia in sickle mice. Recordings were made from single ON, OFF, and Neutral cells in the RVM of sickle and control (HbAA-BERK) mice. Spontaneous activity and responses of ON, OFF and Neutral cells evoked by heat (50 °C) and mechanical (26 g) stimuli applied to the hind paw were compared between sickle and control mice. Although there were no differences in the proportions of functionally-identified neurons or spontaneous activity between sickle and control mice, evoked responses of ON cells to heat and mechanical stimuli were increased approximately 3-fold in sickle mice as compared to control mice. Thus, the RVM contributes to hyperalgesia in sickle mice via a specific ON cell-dependent descending facilitation of nociceptive transmission.

Adolescents and Young Adults With Sickle Cell Disease: Nociplastic Pain and Pain Catastrophizing as Predictors of Pain Interference and Opioid Consumption

OBJECTIVES

Some patients with sickle cell disease (SCD) have features of nociplastic pain. While research suggests that many patients with nociplastic pain consume more opioids due to opioid nonresponsiveness, little is known about the impact of nociplastic pain and pain catastrophizing on opioid consumption and pain interference among adolescents and young adults (AYA) with SCD. The purpose of this study was to (1) characterize nociplastic pain and pain catastrophizing among AYA with SCD, and (2) determine whether these characterizations are associated with subsequent opioid consumption and pain interference 1 month after characterization.

METHODS

Participants completed surveys characterizing nociplastic pain and catastrophizing at a routine clinic visit (baseline). Thereafter, participants received weekly text messages that included pain interference and opioid consumption surveys. Multipredictor 2-part models were used to evaluate the predictive relationships between baseline characterizations and subsequent pain interference, and opioid consumption.

RESULTS

Forty-eight AYA aged 14 to 35 completed baseline measures. Twenty-five percent of participants had scores suggestive of nociplastic pain. Greater nociplastic pain features significantly increased the odds of consuming opioids (odds ratio=1.2) and having greater interference from pain (odds ratio=1.46). Regression analyses found that greater baseline nociplastic pain characteristics were significantly associated with opioid consumption (β=0.13) and pain interference (β=0.061); whereas higher pain catastrophizing scores predicted less opioid consumption (β=-0.03) and less pain interference (β=-0.0007).

DISCUSSION

In this sample of AYA with SCD, features of nociplastic pain predicted higher subsequent opioid consumption and pain interference. Being aware of nociplastic pain features in patients with SCD may better guide individualized pain management.

Analysis of AVPR1A, thermal and pressure pain thresholds, and stress in sickle cell disease

Aim

In patients with sickle cell disease (SCD), negative physical and emotional experiences result from intense chronic and acute pain episodes, but factors underlying these, and their interactions, are not well understood. The arginine vasopressin receptor 1a gene (AVPR1A) single nucleotide polymorphism rs10877969 has been previously associated with aspects of acute pain and stress related pain. In this study, we tested for associations between this SNP, thermal and pressure pain thresholds, clinical pain, and stress in people with SCD.

Methods

150 adults enrolled with SCD completed pain intensity measures (Average Pain Intensity, API) and the Perceived Stress Questionnaire (PSQ). Thermal and pressure pain threshold data were available from quantitative sensory testing (QST), and rs10877969 genotypes were obtained.

Results

In models adjusted for age and gender, between rs10877969 genotypes, we observed no significant differences in thermal (cold, p = 0.66; heat, p = 0.91) and mechanical (pressure, p = 0.33) pain thresholds. The association of rs10877969 with API (p = 0.09) was borderline, but non-significant with PSQ (p = 0.51). The correlation between clinical pain and environmental stress was significant, r = 0.18, p = 0.024, however, the interaction of genotype and PSQ was not significant (p = 0.63).

Conclusion

Clinical and experimental pain were not significantly associated with the rs10877969 genotype. The rs10877969 genotype did not moderate the correlation between environmental stress and clinical pain in this population. However, a trend toward a protective T allele effect on average pain rating in SCD warrants future exploration of this SNP/gene in SCD.

Clinical Assessment of Mechanical Allodynia in Youth With Complex Regional Pain Syndrome: Development and Preliminary Validation of the Pediatric Tactile Sensitivity Test of Allodynia (Pedi-Sense)

Youth with complex regional pain syndrome (CRPS) commonly experience mechanical allodynia and disability. Assessment of mechanical allodynia is typically binary (present or absent), making it difficult to assess the quality and degree of mechanical allodynia before and after treatment. This study developed and validated the Pediatric Tactile Sensitivity Test of Allodynia (Pedi-Sense) to provide an easy way for rehabilitation clinicians to evaluate mechanical allodynia before and after intensive interdisciplinary pain treatment. The 6 Pedi-Sense items demonstrated adequate internal consistency reliability (CR) at admission (CR = .956) and discharge (CR = .973), reasonably fit the hypothesized linear model of stimulus intensity (P < .0001), and significantly loaded onto a single latent factor, mechanical allodynia (P < .0001), at admission and discharge. Pedi-Sense scores significantly correlated with disability (r_s = .40; P = .004) and pain catastrophizing (r_s = .33; P = .017) at admission. The Pedi-Sense appeared responsive to intervention as participants' total scores improved by 1.44 points (95% CI: .72, 2.15) after IIPT interventions that included daily tactile desensitization. However, test-retest and interrater reliability and the specific contribution of desensitization treatment to the overall success of multi-modal pain rehabilitation still needs to be evaluated. PERSPECTIVE: This article presents the development and preliminary validation of a novel clinical assessment of static and dynamic mechanical allodynia. The Pediatric Tactile Sensitivity Test of Allodynia (Pedi-Sense) allows rehabilitation clinicians to easily evaluate mechanical allodynia at the bedside with minimal training and simple equipment to guide desensitization treatment in clinical settings.

Prevalence of neuropathic pain in adolescents with sickle cell disease: A single-center experience

BACKGROUND

Neuropathic pain (NP) has been previously explored in adolescents with sickle cell disease (SCD). This study aims to describe the prevalence of NP in adolescents with SCD at a single institution and to explore associated risk factors.

PROCEDURE

We used the painDETECT questionnaire, one of the few pain phenotyping questionnaires validated for adolescents. We also evaluated the relationships between painDETECT scores and frequency of acute care visits and admissions for pain in the previous 12 months, and age, respectively. Patients 12-18 years old were surveyed from June to July 2019. A retrospective approach was used to answer the remaining research questions.

RESULTS

Eighty-one and seven surveys were completed in the outpatient and inpatient settings, respectively. PainDETECT scores suggestive of NP were more prevalent in inpatient surveys than in outpatient surveys. The difference between the mean painDETECT scores of each group was significant when using a general linear mixed model. Most inpatients surveyed had ≥3 pain events in the previous 12 months. Further, older age and increased number of pain events in the previous 12 months were independently associated with higher painDETECT scores.

CONCLUSIONS

Overall, in our opinion, NP is not being evaluated for and treated sufficiently in pediatric SCD, especially in the setting of inpatient acute vaso-occlusive crisis. Age and number of acute pain events/admissions in the previous 12 months can be used to identify patients likely to be at risk for NP. It is important to continue to identify NP and develop NP-targeting treatment plans.

Nursing Education for the Acute Care Nurse on Pain Mechanisms of Sickle Cell Disease

Background It is unknown whether nurses' knowledge about pain among patients with sickle cell disease (SCD) reflects the current standard of care. The authors evaluated changes in nurses' knowledge and simulated practice behavior after a continuing education program. Method Inpatient nurses completed an e-learning program on SCD pain; a pretest and a posttest with the same 10 questions; and two patient cases with four pain intervention options at the posttest. Results On the pretest, the mean percentage of correct answers was 83% (SD = 13%). The mean percentage of correct answers increased by 12% (p < .0001) on the posttest. For the first simulated patient case, 100% (n = 31) of the nurses selected an appropriate pain intervention option based on the patient-reported pain score. For the second simulated patient case, 84% (n = 26) did so. Conclusion Increased knowledge does not always translate into simulated practice change. The reasons for this are unknown, but they could include implicit bias from exposure to patients who have high use of acute care, although the minority of patients with SCD fit this description. [J Contin Educ Nurs. 2022;53(3):137-144.].

Assessment of pain associated with chronic pancreatitis: An international consensus guideline

Pain is the most common symptom in chronic pancreatitis (CP) with a major impact on quality of life. Few validated questionnaires to assess pain in CP exist, and the lack of consensus negatively impacts clinical management, research and meta-analysis. This guideline aims to review generic pain questionnaires for their usability in CP, to outline how pain assessment can be modified by confounding factors and pain types, to assess the value of additional measures such as quality of life, mental health and quantitative sensory testing, and finally to review pain assessment questionnaires used specifically in CP. A systematic review was done to answer 27 questions that followed the PICO (Population; Intervention; Comparator; Outcome) template. Quality of evidence of the statements was judged by Grades of Recommendation, Assessment, Development and Evaluation (GRADE) criteria. The manuscript was sent for review to 36 experts from various disciplines and continents in a multi-stage Delphi process, and finally reviewed by patient representatives. Main findings were that generic pain instruments are valid in most settings, but aspects of pain are specific for CP (including in children), and instruments have to account for the wide phenotypic variability and development of sensitization of the central nervous system. Side effects to treatment and placebo effects shall also be considered. Some multidimensional questionnaires are validated for CP and are recommended together with assessment of quality of life and psychiatric co-morbidities. This guideline will result in more homogeneous and comprehensive pain assessment to potentially improve management of painful CP.

Gabapentin for acute pain in sickle cell disease: A randomized double-blinded placebo-controlled phase II clinical trial

Pain in sickle cell disease (SCD) can have a neuropathic component. This randomized phase II double-blinded placebo-controlled study evaluated the efficacy of gabapentin in reducing pain and opioid consumption (morphine-equivalent dose [MED]) during acute vaso-occlusive crisis (VOC). Of 90 patients aged 1-18 years with VOC pain, 45 were randomized to a single gabapentin dose (15 mg/kg) and 45 to placebo, in addition to standard treatment; 42 and 44 patients were evaluable in the gabapentin and placebo arms, respectively. A decrease in pain of ≥33% was reported in 68% of patients in the gabapentin arm and 60% of those in the placebo arm (one-sided p = 0.23). The median MED (mg/kg) in the gabapentin (0.12) and placebo arms (0.13) was similar (p = 0.9). However, in the subset of patients with the HbSS genotype (n = 45), the mean (SD) absolute pain score decrease by the time of discharge was significantly greater in the gabapentin arm (5.9 [3.5]) than in the placebo arm (3.6 [3.3]) (p = 0.032). Pain scores in the overall study population were not significantly reduced when gabapentin was added to standard treatment; however, gabapentin benefited individuals with the more severe genotype, HbSS, during acute VOC. Larger, prospective studies are needed to confirm these findings.

Pain in sickle cell disease: current and potential translational therapies

Pain is a major comorbidity of sickle cell disease (SCD). Patients with SCD may suffer from both acute and chronic pain. Acute pain is caused by recurrent and unpredictable episodes of vaso-occlusive crises (VOC), whereas the exact etiology of chronic pain is still unknown. Opioids are the mainstay for pain treatment, but the opioid epidemic has significantly altered access to prescription opioids and has brought concerns over their long-term use into the forefront, which have negatively impacted the treatment of sickle pain. Opioids remain potent analgesics but growing opioid-phobia has led to the realization of an unmet need to develop nonopioid therapies that can provide relief for severe sickle pain. This realization has contributed to the approval of 3 different drugs by the Food and Drug Administration (FDA) for the treatment of SCD, particularly to reduce VOC and/or have an impact on the pathobiology of SCD. In this review, we outline the challenges and need for validation of side-effects of opioids and provide an update on the development of mechanism-based translational therapies, specifically targeting pain in SCD.

Sickle Cell Disease and Pain: Is it all Vaso-occlusive Crises?

OBJECTIVES

Acute pain is the main complication of sickle cell disease. Chronic pain (CP) and neuropathic pain (NP) may also be experienced, but have not been formally described in Jamaican patients. A cross-sectional study was conducted to determine their prevalence and characteristics, and to determine the common pain locations and modalities of management.

MATERIALS AND METHODS

All well individuals with sickle cell disease patients 14 years and older, not pregnant and without a history of clinical stroke were consecutively recruited. Anthropometric measurements, hematology studies, an analgesia checklist, and the Adult Sickle Cell Quality of Life Measurement Information System questionnaire were completed. The painDETECT questionnaire was completed to describe NP and pain patterns-from which CP was defined.

RESULTS

There were 257 patients in total, with 55.6% being females; the mean age of the patients was 31.7±12 years, and 75% had the SS genotype. Almost all patients (92.6%) had had an acute pain crisis in their lifetime and 72.4% in the last year. The mean severity at last attack was 6.8±3.1 on a scale of 0 to 10. The prevalences of CP and NP were 21.5% and 17.9%, respectively. Female sex, the presence of current leg ulcers, and the use of a strong opioid in the last 4 weeks produced higher odds of NP, whereas older age, milder genotypes, and daily analgesic use had the highest odds of CP. Opioids were used by 40.1% of the patients in the previous 4 weeks, whereas nonpharmacological treatments such as physiotherapy was less used, but reported to be very effective.

DISCUSSION

CP and NP should be assessed during routine care of sickle cell pain so that targeted therapies can be applied.

Offset analgesia identifies impaired endogenous pain modulation in pediatric chronic pain disorders

Offset analgesia (OA), a psychophysical test of endogenous pain inhibition, is diminished in many adult chronic pain disorders but OA has not been investigated in youth with chronic pain disorders. This study assessed OA responses in 30 youth with chronic primary and secondary pain disorders and 32 healthy controls. The OA, control, and constant thermal tests were evoked with an individualized noxious heat stimulus of approximately 50/100 mm on a visual analogue scale followed by 1°C offset temperature. This study also examined the association of OA responses with 2 self-report measures of pain sensitivity, the Central Sensitization Inventory (CSI) and Pain Sensitivity Questionnaire. Patients exhibited diminished capacity to activate OA with a reduction in ΔeVASc of 53 ± 29% vs controls 74 ± 24% (P = 0.003) even after multivariate regression adjusting for age, sex, and body mass index. Patients also showed decreased ability to habituate to a constant noxious heat stimulus compared to controls (P = 0.021). Central Sensitization Inventory scores showed excellent predictive accuracy in differentiating patients from controls (area under the curve = 0.95; 95% CI: 0.91-0.99) and CSI score ≥30 was identified as an optimal cutoff value. Pain Sensitivity Questionnaire scores did not differentiate patients from controls nor correlate with OA. In this study, 60% of youth with chronic pain showed reduced capacity for endogenous pain inhibition.

Patient-reported Outcome Measures in Pediatric Non-Malignant Hematology: A Systematic Review

Patient-reported outcome measures (PROMs) are questionnaires completed by patients or caregivers without influence by health care professionals. As such, PROMs show subjective health experiences, enhance the clinical information available to providers, and inform clinical action. The objective of this systematic review is to identify and list which validated PROMs have been used to monitor health-related quality of life in pediatric patients with nonmalignant hematology (hemophilia, immune thrombocytopenia, sickle cell disease, and thalassemia). Databases (MEDLINE, Embase, HaPI, CINAHL, and PsycTESTS) were searched to identify publications that validated or used PROMs as an outcome measure in the 4 disease groups. Overall, 209 articles met the inclusion criteria, identifying 113 PROMs. Of the 113 identified PROMs, 95 are generic and can be used in multiple disease groups. The Pediatric Quality of Life Generic Core Scales was the most frequently used generic PROM (68 studies). The 18 remaining PROMs were disease specific. The results of this review, together with the COSMIN tool for selecting outcome measures, will allow clinicians to evaluate the PROMs that are best suited to their patient population. In addition, the focus groups are currently being conducted with patients, parents, and clinicians to determine the optimal use of PROMs in the clinical environment.

Pain Experience, Physical Function, Pain Coping, and Catastrophizing in Children With Sickle Cell Disease Who Had Normal and Abnormal Sensory Patterns

CONTEXT

Sickle cell disease (SCD) is associated with recurrent pain that could lead to abnormal sensory patterns (ASPs).

OBJECTIVES

The purpose of this study is to compare children with SCD who had normal sensory patterns (NSPs) and ASPs in pain experience, physical function, pain coping, and pain catastrophizing.

METHODS

Children with quantitative sensory testing data were selected from a larger study that examined pain and symptoms in children with SCD. Comparisons were made between children with NSP (n = 35; 13.9 ± 1.9 years) and ASP (n = 13; 12.8 ± 1.9 years). Children completed the Adolescent Pediatric Pain Tool, Functional Disability Inventory, Pain Coping Questionnaire, and Pain Catastrophizing Scale.

RESULTS

No significant differences were found in pain intensity (2.9 ± 3.0 vs. 2.6 ± 2.8 on 0-10 Visual Analogue Scale) between the NSP and ASP, respectively. The most common marked pain sites for both groups were lower extremities (22.9%), head and neck (20.8%), and upper extremities (20.8%). Functional Disability Inventory scores were significantly worse in ASP (38.5%) compared with NSP (11.4%). The ASP group had significantly worse scores in emotion-focused pain coping subscales.

CONCLUSION

Children with SCD with ASP had worse functional disability, were expressing more affective pain quality, and had emotion-focused pain coping compared with NSP. Future studies are needed to examine the effectiveness of physical activities on the physical function as well as psychosocial interventions such as peer support and creative arts expression to minimize development of ASP in children with SCD.

Neuropathic pain is associated with poor health-related quality of life in adolescents with sickle cell disease: A preliminary report

BACKGROUND

Neuropathic pain is associated with poor health-related quality of life (HRQL) in pain conditions other than sickle cell disease (SCD); this relationship in SCD is unknown. We investigated this relationship and hypothesized neuropathic pain is associated with poor HRQL in adolescents with SCD.

METHODS

We conducted a cross-sectional study of patients with SCD ages 13-18 years during baseline health. Primary outcome was HRQL, assessed by the PedsQL SCD Module (child self-report, parent proxy report). PedsQL is scored from 0 to 100, with higher scores indicating better HRQL. Neuropathic pain was assessed using the painDETECT questionnaire (scored 0-38); higher scores indicated greater likelihood of neuropathic pain. All completed both PedsQL SCD Module and painDETECT questionnaire. Descriptive statistics were used and associations between painDETECT and PedsQL Total Score, Pain Impact, Pain and Hurt, and Pain Management and Control Scores were determined via Pearson correlation. Significance was P < .05.

RESULTS

Twelve patients were enrolled. Median (interquartile range [IQR]) age was 15 (14-16.5) years, 75% were female, and 83% were on hydroxyurea. Higher painDETECT scores were significantly associated with lower PedsQL SCD Module child self-report Pain and Hurt Scores (r = -0.68, P = .01). Higher painDETECT scores were also significantly associated with lower PedsQL parent proxy-report Total Scores (r = -0.64, P = .03) and Pain and Hurt Scores (r = -0.67, P = .02).

CONCLUSIONS

These data suggest that adolescents with SCD and neuropathic pain have poor HRQL even in their baseline state of health. Prospective, larger studies are needed to confirm this preliminary finding and explore a multimodal approach for pain assessment in SCD.

Spatiotemporal Alterations in Gait in Humanized Transgenic Sickle Mice

Sickle cell disease (SCD) is a hemoglobinopathy affecting multiple organs and featuring acute and chronic pain. Purkinje cell damage and hyperalgesia have been demonstrated in transgenic sickle mice. Purkinje cells are associated with movement and neural function which may influence pain. We hypothesized that Purkinje cell damage and/or chronic pain burden provoke compensatory gait changes in sickle mice. We found that Purkinje cells undergoe increased apoptosis as shown by caspase-3 activation. Using an automated gait measurement system, MouseWalker, we characterized spatiotemporal gait characteristics of humanized transgenic BERK sickle mice in comparison to control mice. Sickle mice showed alteration in stance instability and dynamic gait parameters (walking speed, stance duration, swing duration and specific swing indices). Differences in stance instability may reflect motor dysfunction due to damaged Purkinje cells. Alterations in diagonal and all stance indices indicative of hesitation during walking may originate from motor dysfunction and/or arise from fear and/or anticipation of movement-evoked pain. We also demonstrate that stance duration, diagonal swing indices and all stance indices correlate with both mechanical and deep tissue hyperalgesia, while stance instability correlates with only deep tissue hyperalgesia. Therefore, objective analysis of gait in SCD may provide insights into neurological impairment and pain states.

Integrative approaches to treating pain in sickle cell disease: Pre-clinical and clinical evidence

Sickle cell disease (SCD) is a genetic disorder characterized by hemolysis, end-organ damage, inflammation, and pain. Recurrent and unpredictable episodes of acute pain due to vaso-occlusive crises are a unique feature of SCD. Many patients also develop lifelong chronic pain. Opioids are the primary method of pain treatment in SCD; however, continued use is associated with several adverse effects. Integrative approaches to treating pain in SCD are increasingly being explored to prevent the side effects associated with opioids. In this review, we highlight the mechanisms of pain in SCD and describe mechanism-based integrative approaches for treating pain.

Autonomically-mediated decrease in microvascular blood flow due to mental stress and pain in sickle cell disease: A target for neuromodulatory interventions

Pain and vaso-occlusive crises (VOC) are hallmark complications of sickle cell disease (SCD) and result in significant physical and psychosocial impairment. The variability in SCD pain frequency and triggers for the transition from steady state to VOC are not well understood. This paper summarizes the harmful physiological effects of pain and emotional stressors on autonomically-mediated vascular function in individuals with SCD and the effects of a cognitive, neuromodulatory intervention (i.e. hypnosis) on microvascular blood flow. We reviewed recent studies from the authors' vascular physiology laboratory that assessed microvascular responses to laboratory stressors in individuals with SCD. Results indicate that participants with SCD exhibit marked neurally mediated vascular reactivity in response to pain, pain-related fear, and mental stress. Further, pilot study results show that engagement in hypnosis may attenuate harmful microvascular responses to pain. The collective results demonstrate that autonomically-mediated vascular responses to pain and mental stress represent an important SCD intervention target. This ongoing work provides physiological justification for the inclusion of cognitive, neuromodulatory and complementary treatments in SCD disease management and may inform the development of targeted, integrative interventions that prevent the enhancement of autonomic vascular dysfunction in SCD.

Relationship of Pain Quality Descriptors and Quantitative Sensory Testing: Sickle Cell Disease

BACKGROUND

Chronic pain in adults with sickle cell disease (SCD) may be the result of altered processing in the central nervous system, as indicated by quantitative sensory testing (QST). Sensory pain quality descriptors on the McGill Pain Questionnaire (MPQ) are indicators of typical or altered pain mechanisms but have not been validated with QST-derived classifications.

OBJECTIVES

The specific aim of this study was to identify the sensory pain quality descriptors that are associated with the QST-derived normal or sensitized classifications. We expected to find that sets of sensory pain quality descriptors would discriminate the classifications.

METHODS

A cross-sectional quantitative study of existing data from 186 adults of African ancestry with SCD. Variables included MPQ descriptors, patient demographic data, and QST-derived classifications.

RESULTS

The participants were classified as central sensitization (n = 33), mixed sensitization (n = 23), and normal sensation. Sensory pain quality descriptors that differed statistically between mixed sensitization and central sensation compared to normal sensitization included cold (p = .01) and spreading (p = .01). Aching (p = .01) and throbbing (p = .01) differed statistically between central sensitization compared with mixed sensitization and normal sensation. Beating (p = .01) differed statistically between mixed sensitization compared with central sensitization and normal sensation. No set of sensory pain quality descriptors differed statistically between QST classifications.

DISCUSSION

Our study is the first to examine the association between MPQ sensory pain quality descriptors and QST-derived classifications in adults with SCD. Our findings provide the basis for the development of a MPQ subscale with potential as a mechanism-based screening tool for neuropathic pain.

Sensitivities to Thermal and Mechanical Stimuli: Adults With Sickle Cell Disease Compared to Healthy, Pain-Free African American Controls

Evidence supports^, but is inconclusive that sensitization contributes to chronic pain in some adults with sickle cell disease (SCD). We determined the prevalence of pain sensitization among adults with SCD pain compared with pain-free healthy adults. In a cross sectional, single session study of 186 African American outpatients with SCD pain (age 18-74 years, 59% female) and 124 healthy age, gender, and race matched control subjects (age 18-69 years, 49% female), we compared responses to standard thermal (Medoc TSA II) and mechanical stimuli (von Frey filaments). Although we observed no significant differences in thermal thresholds between controls and patients, patients with SCD had lower pain thresholds to mechanical stimuli and reported higher pain intensity scores to all thermal and mechanical stimuli at a non-painful body site. Compared with controls, about twice as many patients with SCD showed sensitization: 12% versus 23% at the anterior forearm site (P = .02), and 16% versus 32% across 3 tested sites (P = .004). Among patients with SCD, 18% exhibited some element of central sensitization. Findings indicate that persistent allodynia and hyperalgesia can be part of the SCD pain experience and should be considered when selecting therapies for SCD pain. PERSPECTIVE: Compared with matched healthy controls, quantitative sensory testing in adults with pain and sickle cell disease (SCD) demonstrates higher prevalence of sensitization, including central sensitization. The findings of allodynia and hyperalgesia may indicate neuropathic pain and could contribute to a paradigm shift in assessment and treatment of SCD pain.

A QST-based Pain Phenotype in Adults With Sickle Cell Disease: Sensitivity and Specificity of Quality Descriptors

BACKGROUND

We sought to refine a screening measure for discriminating a sensitized or normal sensation pain phenotype among African American adults with sickle cell disease (SCD).

OBJECTIVE

To develop scoring schemes based on sensory pain quality descriptors; evaluate their performance on classifying patients with SCD who had sensitization or normal sensation, and compare with scores on the Self-report Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS) and the Neuropathic Pain Symptom Inventory (NPSI).

METHODS

Participants completed PAINReportIt, quantitative sensory testing (QST), S-LANSS, and NPSI. Conventional binary logistic regression and least absolute shrinkage and selection operator (lasso) regression were used to obtain 2 sets of weights resulting in 2 scores: the PR-Logistic (PAINReportIt score weighted by conventional binary logistic regression coefficients) and PR-Lasso (PAINReportIt score weighted by lasso regression coefficients). Performance of the proposed scores and the existing scores were evaluated.

RESULTS

Lasso regression resulted in a parsimonious model with non-zero weights assigned to 2 neuropathic descriptors, cold and spreading. We found positive correlations between the PR-Lasso and other scores: S-LANSS (r = 0.22, P < 0.01), NPSI (r = 0.22, P < 0.01), and PR-Logistic (r = 0.35, P < 0.01). The NPSI and PR-Lasso performed similarly at different levels of required specificity and outperformed the S-LANSS and PR-Logistic at the various specificity points.

CONCLUSION

The PR-Lasso offers a way to discriminate a SCD pain phenotype.

Gabapentin alleviates chronic spontaneous pain and acute hypoxia-related pain in a mouse model of sickle cell disease

Pain is the main complication of sickle cell disease (SCD). Individuals with SCD experience acute pain episodes and chronic daily pain, both of which are managed with opioids. Opioids have deleterious side effects and use-associated stigma that make them less than ideal for SCD pain management. After recognizing the neuropathic qualities of SCD pain, clinically-approved therapies for neuropathic pain, including gabapentin, now present unique non-opioid based therapies for SCD pain management. These experiments explored the efficacy of gabapentin in relieving evoked and spontaneous chronic pain, and hypoxia/reoxygenation (H/R)-induced acute pain in mouse models of SCD. When administered following H/R, a single dose of gabapentin alleviated mechanical hypersensitivity in SCD mice by decreasing peripheral fibre activity. Gabapentin treatment also alleviated spontaneous ongoing pain in SCD mice. Longitudinal daily administration of gabapentin failed to alleviate H/R-induced pain or chronic evoked mechanical, cold or deep tissue hypersensitivity in SCD mice. Consistent with this observation, voltage-gated calcium channel (VGCC) α₂ δ₁ subunit expression was similar in sciatic nerve, dorsal root ganglia and lumbar spinal cord tissue from SCD and control mice. Based on these data, gabapentin may be an effective opioid alternative for the treatment of chronic spontaneous and acute H/R pain in SCD.

Sickle cell disease: Clinical presentation and management of a global health challenge

Sickle cell disease is an autosomal recessive, multisystem disorder, characterised by chronic haemolytic anaemia, painful episodes of vaso-occlusion, progressive organ failure and a reduced life expectancy. Sickle cell disease is the most common monogenetic disease, with millions affected worldwide. In well-resourced countries, comprehensive care programs have increased life expectancy of sickle cell disease patients, with almost all infants surviving into adulthood. Therapeutic options for sickle cell disease patients are however, still scarce. Predictors of sickle cell disease severity and a better understanding of pathophysiology and (epi)genetic modifiers are warranted and could lead to more precise management and treatment. This review provides an extensive summary of the pathophysiology and management of sickle cell disease and encompasses the characteristics, complications and current and future treatment options of the disease.

Sensitization of nociceptors and dorsal horn neurons contributes to pain in sickle cell disease

Sickle cell disease (SCD) describes a group of disorders associated with a point mutation in the beta chain of hemoglobin. The mutation leads to the creation of sickle hemoglobin (HbS) and causes distortion of erythrocytes through polymerization under low oxygen, resulting in characteristic sickle red blood cells. Vaso-occlusion episodes caused by accumulation of sRBCs results in ischemia-reperfusion injury, reduced oxygen supply to organs, oxidative stress, organ damage and severe pain that often requires hospitalization and opioid treatment. Further, many patients suffer from chronic pain, including hypersensitivity to heat and cold stimuli. Progress towards the development of novel strategies for both acute and chronic pain in patients with SCD has been impeded by a lack of understanding the mechanisms underlying pain in SCD. The purpose of this review is to highlight evidence for the contribution of peripheral and central sensitization that leads to widespread, chronic pain and hyperalgesia. Targeting the mechanisms that initiate and maintain sensitization in SCD might offer effective approaches to manage the severe and debilitating pain associated with this condition.

Quantitative sensory testing in children with sickle cell disease: additional insights and future possibilities

Quantitative sensory testing (QST) is used in a variety of pain disorders to characterize pain and predict prognosis and response to specific therapies. In this study, we aimed to confirm results in the literature documenting altered QST thresholds in sickle cell disease (SCD) and assess the test-retest reliability of results over time. Fifty-seven SCD and 60 control subjects aged 8-20 years underwent heat and cold detection and pain threshold testing using a Medoc TSAII. Participants were tested at baseline and 3 months; SCD subjects were additionally tested at 6 months. An important facet of our study was the development and use of a novel QST modelling approach, allowing us to model all data together across modalities. We have not demonstrated significant differences in thermal thresholds between subjects with SCD and controls. Thermal thresholds were consistent over a 3- to 6-month period. Subjects on whom hydroxycarbamide (HC) was initiated shortly before or after baseline testing (new HC users) exhibited progressive decreases in thermal sensitivity from baseline to 6 months, suggesting that thermal testing may be sensitive to effective therapy to prevent vasoocclusive pain. These findings inform the use of QST as an endpoint in the evaluation of preventative pain therapies.

Immune cell neural interactions and their contributions to sickle cell disease

Sickle cell disease (SCD) is characterized by hemolysis, inflammation, and pain. Mechanisms of pain manifestation are complex, and there is a major gap in knowledge of how the nervous and immune systems interact to contribute to pain and other comorbidities in SCD. Sterile inflammation in the periphery and central nervous system contributes to vascular and neural activation. Cellular and soluble mediators create an inflammatory and neuroinflammatory microenvironment contributing to neurogenic inflammation and acute and chronic pain. In this review we highlight relevant neuro-immune interactions that contribute to the pathobiology of SCD.

Patients with sickle-cell disease exhibit greater functional connectivity and centrality in the locus coeruleus compared to anemic controls

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Patients with sickle-cell disease (SCD) have greater resting-state functional connectivity between the locus coeruleus (LC) and dorsolateral prefrontal cortex (dlPFC).

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Patients with SCD have greater resting state centrality of the LC

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SCD patients with chronic pain exhibited even greater functional connectivity between the LC and dlPFC.

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This study supports hyper-connectivity between the LC and PFC is a potential chronic pain generator.

Vaso-occlusive crisis in sickle cell disease: current paradigm on pain management

This narrative review aims to highlight the current paradigm on pain management in sickle cell vaso-occlusive crisis. It specifically examines the pathophysiologic mechanisms of sickle cell pain as well as the pharmacologic and nonpharmacologic methods of pain management. Recurrent painful episodes constitute the major morbidity in sickle cell disease (SCD). While adolescents and young adults experience mostly acute episodic nociceptive pain, it is now recognized that a significant number of adult patients develop chronic neuropathic and centralized pain. In fact, current evidence points to an age-dependent increase in the frequency of SCD patients with chronic pain. Management of disease-related pain should be based on its pathophysiologic mechanisms instead of using recommendations from other non-SCD pain syndromes. Pain management in vaso-occlusive crisis is complex and requires multiple interventions such as pharmacologic, nonpharmacologic, and preventive therapeutic interventions. Pharmacologic treatment involves the use of non-opioid and opioid analgesics, and adjuvants - either singly or in combination - depending on the severity of pain. The basic approach is to treat SCD pain symptomatically with escalating doses of non-opioid and opioid analgesics. Given the moderate-to-severe nature of the pain usually experienced in this form of SCD crisis, opioids form the bedrock of pharmacologic treatment. Multimodal analgesia and structured, individualized analgesic regimen appear more effective in achieving better treatment outcomes. Although the current evidence is still limited on the supportive role of cognitive behavioral therapy in pain management, this nonpharmacologic approach is reportedly effective, but needs further exploration as a possible adjunct in analgesia.

Neuronal transient receptor potential (TRP) channels and noxious sensory detection in sickle cell disease

Pain is the leading cause for hospitalization in patients with sickle cell disease (SCD). While the characteristics of SCD pain can vary widely between patients and between phases of the disease (e.g. vasoocclusive crisis pain vs. chronic pain), similar neuronal mechanisms likely underlie the various aspects of nociceptive processing. In the peripheral nervous system, small unmyelinated C fibers and lightly-myelinated Aδ fibers detect and transmit noxious stimuli. Both classes of neurons express members of the transient receptor potential (TRP) family, a group of ligand gated ion-channels that are activated by thermal, chemical, and mechanical stimuli. Promiscuous TRP channel family members are activated by a wide range of stimuli, many of which are dysregulated in patients with SCD and transgenic SCD mouse models. In 2011, our lab published the first report of TRP channel contributions to rodent SCD pain. Since that time, additional basic and clinical research efforts have investigated the genetic and biochemical status of TRP channels in SCD, placing particular focus on TRPV1. This review will discuss these advances and highlight the clinical SCD presentations that have not yet been studied, but which may be mediated by TRP channel activity.

Mouse Models of Pain in Sickle Cell Disease

Sickle cell disease (SCD) is a genetic blood disorder that impacts millions of individuals worldwide. SCD is characterized by debilitating pain that can begin during infancy and may continue to increase throughout life. This pain can be both acute and chronic. A characteristic feature specific to acute pain in SCD occurs during vaso-occlusive crisis (VOC) due to the blockade of capillaries with sickle red blood cells. The acute pain of VOC is intense, unpredictable, and requires hospitalization. Chronic pain occurs in a significant population with SCD. Treatment options for sickle pain are limited and primarily involve the use of opioids. However, long-term opioid use is associated with numerous side effects. Thus, pain management in SCD remains a major challenge. Humanized transgenic mice expressing exclusively human sickle hemoglobin show features of pain and pathobiology similar to that in patients with SCD. Therefore, these mice offer the potential for investigating the mechanisms of pain in SCD and allow for development of novel targeted analgesic therapies. © 2018 by John Wiley & Sons, Inc.

Targeting pain at its source in sickle cell disease

Sickle cell disease (SCD) is a genetic disorder associated with hemolytic anemia, end-organ damage, reduced survival, and pain. One of the unique features of SCD is recurrent and unpredictable episodes of acute pain due to vasoocclusive crisis requiring hospitalization. Additionally, patients with SCD often develop chronic persistent pain. Currently, sickle cell pain is treated with opioids, an approach limited by adverse effects. Because pain can start at infancy and continue throughout life, preventing the genesis of pain may be relatively better than treating the pain once it has been evoked. Therefore, we provide insights into the cellular and molecular mechanisms of sickle cell pain that contribute to the activation of the somatosensory system in the peripheral and central nervous systems. These mechanisms include mast cell activation and neurogenic inflammation, peripheral nociceptor sensitization, maladaptation of spinal signals, central sensitization, and modulation of neural circuits in the brain. In this review, we describe potential preventive/therapeutic targets and their targeting with novel pharmacologic and/or integrative approaches to ameliorate sickle cell pain.

Pressure Pain Threshold and Anxiety in Adolescent Females With and Without Juvenile Fibromyalgia: A Pilot Study

OBJECTIVES

Reduced pain thresholds have been documented in adult fibromyalgia, but there are no quantitative studies of altered pain sensitivity in adolescents with juvenile fibromyalgia (JFM). The current study examined differences in pressure pain sensitivity between adolescent females with JFM and healthy controls. The relationship between levels of anxiety and pain were also examined.

METHODS

A total of 34 JFM (15.4±1.4 y old) and 31 controls (14.5±1.3 y old) completed self-report measures of pain and anxiety. Pressure pain threshold was assessed (palm and forehead sites) with a hand-held algometer. Participants indicated the first sensation of pain and then rated the intensity of pain on a Numerical Rating Scale.

RESULTS

Adolescents with JFM exhibited greater sensitivity to pressure pain compared with controls. While the difference between JFM and controls was only observed at the forehead, the intensity of pain produced by the pressure algometry at both sites was significantly higher in the JFM participants compared with controls. Correlations between clinical pain and anxiety were significant for the JFM group only. No relationships were observed between anxiety and pressure pain for either group.

DISCUSSION

This study is a first step toward investigating mechanisms of altered pain processing in adolescents with JFM. Adolescents with JFM were found be more sensitive to pressure pain than their healthy peers, which suggests a propensity for sensitization of peripheral and/or central nociceptive information often reported in adult fibromyalgia, and which does not appear to be affected by anxiety.

Targeting novel mechanisms of pain in sickle cell disease

Patients with sickle cell disease (SCD) suffer from intense pain that can start during infancy and increase in severity throughout life, leading to hospitalization and poor quality of life. A unique feature of SCD is vaso-occlusive crises (VOCs) characterized by episodic, recurrent, and unpredictable episodes of acute pain. Microvascular obstruction during a VOC leads to impaired oxygen supply to the periphery and ischemia reperfusion injury, inflammation, oxidative stress, and endothelial dysfunction, all of which may perpetuate a noxious microenvironment leading to pain. In addition to episodic acute pain, patients with SCD also report chronic pain. Current treatment of moderate to severe pain in SCD is mostly reliant upon opioids; however, long-term use of opioids is associated with multiple side effects. This review presents up-to-date developments in our understanding of the pathobiology of pain in SCD. To help focus future research efforts, major gaps in knowledge are identified regarding how sickle pathobiology evokes pain, pathways specific to chronic and acute sickle pain, perception-based targets of "top-down" mechanisms originating from the brain and neuromodulation, and how pain affects the sickle microenvironment and pathophysiology. This review also describes mechanism-based targets that may help develop novel therapeutic and/or preventive strategies to ameliorate pain in SCD.

Pain-measurement tools in sickle cell disease: where are we now?

Pain is a complex multidimensional experience and the most common morbidity in patients with sickle cell disease (SCD). Tools to assess pain can be of use not only to guide pain treatment but also to provide insight into underlying pain neurobiology. Mechanisms of pain in SCD are multifactorial and are not completely elucidated. Although vaso-occlusion of microcirculation by sickled red cells is believed to be the underlying mechanism of acute vaso-occlusive pain, mechanisms for chronic pain and the transition from acute to chronic pain are under investigation. A number of modalities can be used in clinical practice and/or research to capture various dimensions of pain. Selection of a pain-assessment tool should be directed by the purpose of the assessment. Pain-assessment tools, many of which are currently in the early stages of validation, are discussed here. Development and validation of these multimodal tools is crucial for developing improved understanding of SCD pain and its management.

Targeting novel mechanisms of pain in sickle cell disease

Patients with sickle cell disease (SCD) suffer from intense pain that can start during infancy and increase in severity throughout life, leading to hospitalization and poor quality of life. A unique feature of SCD is vaso-occlusive crises (VOCs) characterized by episodic, recurrent, and unpredictable episodes of acute pain. Microvascular obstruction during a VOC leads to impaired oxygen supply to the periphery and ischemia reperfusion injury, inflammation, oxidative stress, and endothelial dysfunction, all of which may perpetuate a noxious microenvironment leading to pain. In addition to episodic acute pain, patients with SCD also report chronic pain. Current treatment of moderate to severe pain in SCD is mostly reliant upon opioids; however, long-term use of opioids is associated with multiple side effects. This review presents up-to-date developments in our understanding of the pathobiology of pain in SCD. To help focus future research efforts, major gaps in knowledge are identified regarding how sickle pathobiology evokes pain, pathways specific to chronic and acute sickle pain, perception-based targets of "top-down" mechanisms originating from the brain and neuromodulation, and how pain affects the sickle microenvironment and pathophysiology. This review also describes mechanism-based targets that may help develop novel therapeutic and/or preventive strategies to ameliorate pain in SCD.

Characterization of a mouse model of sickle cell trait: parallels to human trait and a novel finding of cutaneous sensitization

Sickle cell trait (SCT) has classically been categorized as a benign condition except in rare cases or upon exposure to severe physical conditions. However, several lines of evidence indicate that individuals with SCT are not always asymptomatic, and additional physiological changes and risks may remain unexplored. Here, we utilized mice harbouring one copy of normal human β globin and one copy of sickle human β globin as a model of SCT to assess haematological, histopathological and somatosensory outcomes. We observed that SCT mice displayed renal and hepatic vascular congestion after exposure to hypoxia. Further, we observed that SCT mice displayed increased cold aversion as well as mechanical and heat sensitivity, though to a lesser degree than homozygous sickle cell disease mice. Notably, mechanical hypersensitivity increased following hypoxia and reoxygenation. Overall our findings suggest that SCT is not entirely benign, and further assessment of pain and cutaneous sensitization is warranted both in animal models and in clinical populations.

Central sensitization associated with low fetal hemoglobin levels in adults with sickle cell anemia

BACKGROUND AND AIMS

Pain is the hallmark of sickle cell anemia (SCA), presenting as recurrent acute events or chronic pain. Central sensitization, or enhanced excitability of the central nervous system, alters pain processing and contributes to the maintenance of chronic pain. Individuals with SCA demonstrate enhanced sensitivity to painful stimuli however central mechanisms of pain have not been fully explored. We hypothesized that adults with SCA would show evidence of central sensitization as observed in other diseases of chronic pain.

METHODS

We conducted a prospective study of static and dynamic quantitative sensory tests in 30 adults with SCA and 30 matched controls.

RESULTS

Static thermal testing using cold stimuli showed lower pain thresholds (p=0.04) and tolerance (p=0.04) in sickle cell subjects, but not for heat. However, SCA subjects reported higher pain ratings with random heat pulses (p<0.0001) and change in scores with temporal summation at the heat pain threshold (p=0.002). Similarly, with the use of pressure pain stimuli, sickle cell subjects reported higher pain ratings (p=0.04), but not higher pressure pain tolerance/thresholds or allodynia to light tactile stimuli. Temporal summation pain score changes using 2 pinprick probes (256 and 512mN) were significantly greater (p=0.004 and p=0.008) with sickle cell, and delayed recovery was associated with lower fetal hemoglobin (p=0.002 and 0.003).

CONCLUSIONS

Exaggerated temporal summation responses provide evidence of central sensitization in SCA.

IMPLICATIONS

The association with fetal hemoglobin suggests this known SCA modifier may have a therapeutic role in modulating central sensitization.

A population-based study of quantitative sensory testing in adolescents with and without chronic pain

Quantitative sensory testing (QST) has been used to characterize pain sensitivity in individuals with and without pain conditions. Research remains limited in pediatric populations, hindering the ability to expand the utility of QST toward its potential application in clinical settings and clinical predictive value. The aims of this study were to examine pain sensitivity using QST in adolescents with chronic pain compared to adolescents without chronic pain and identify predictors of pain sensitivity. A population-based study conducted from 2010 to 2011 provided data on 941 adolescents, 197 were classified as having chronic pain and 744 were classified without chronic pain. Self-reported data on pain characteristics, psychological functioning, and QST responses were examined. The findings revealed lower pressure pain threshold and tolerance on the trapezius (P's = 0.03) in adolescents with chronic pain compared to adolescents without chronic pain, but no differences on heat or cold-pressor pain tasks. Female sex (P's = 0.02) and poorer psychological functioning (P's = 0.02) emerged as significant predictors of greater pain sensitivity across all pain modalities. Exploratory analyses revealed several associations between clinical pain characteristics and QST responses within the chronic pain cohort. Findings from this large pediatric sample provide comprehensive data that could serve as normative data on QST responses in adolescents with and without chronic pain. These findings lay the groundwork toward developing future QST research and study protocols in pediatric populations, taking into consideration sex and psychological distress.

Substance P is increased in patients with sickle cell disease and associated with haemolysis and hydroxycarbamide use

Sickle cell disease (SCD) pain transitions from acute to chronic for unknown reasons. Chronic elevation of the pain neurotransmitter substance P (SP) sensitizes pain nociceptors. We evaluated SP levels in controls and SCD patients during baseline and acute pain and investigated associations between SP and age, gender, pain history, haemolysis and hydroxycarbamide (also termed hydroxyurea) use. Plasma SP levels were measured using enzyme-linked immunosorbent assay. Independent samples t-test compared SP levels between: (i) SCD baseline and controls, and (ii) SCD baseline and acute pain. Multivariate linear regression determined associations between SP and age, gender, pain history and hydroxycarbamide use. Spearman correlation determined an association between SP and haemolysis. We enrolled 35 African American controls, 25 SCD baseline and 12 SCD pain patients. SCD patients were 7-19 years old. Mean ± standard deviation SP level (pg/ml) in SCD baseline was higher than controls (32·4 ± 11·6 vs. 22·9 ± 7·6, P = 0·0009). SP in SCD pain was higher than baseline (78·1 ± 43·4 vs. 32·4 ± 11·6, P = 0·004). Haemolysis correlated with increased SP: Hb (r = -0·7, P = 0·0002), reticulocyte count (r = 0·61, P = 0·0016), bilirubin (r = 0·68, P = 0·0216), lactate dehydrogenase (r = 0·62, P = 0·0332), aspartate aminotransferase (r = 0·68, P = 0·003). Patients taking hydroxycarbamide had increased SP (β = 29·2, P = 0·007). SP could be a mediator of or marker for pain sensitization in SCD and a biomarker and/or target for novel pain treatment.

Clinical Interpretation of Quantitative Sensory Testing as a Measure of Pain Sensitivity in Patients With Sickle Cell Disease

Patients with sickle cell disease (SCD) display significantly lower mean/median thermal and mechanical pain thresholds compared with controls. This suggests impaired pain sensitivity where stimuli produce exaggerated pain. Despite these mean/median differences, clinicians need to understand if patients meet criteria for impaired pain sensitivity. We defined thresholds for impaired cold, heat, and mechanical pain sensitivity in SCD patients. Using quantitative sensory testing (QST) we assessed cold, heat, and mechanical pain thresholds in SCD patients and African American controls aged 7 years and above. Impaired pain sensitivity was defined as: (1) cold pain threshold 1 SD above control median threshold; (2) heat pain threshold 1 SD below control median threshold; and (3) mechanical pain threshold 1 SD below control median threshold. Fifty-five SCD patients and 57 controls participated in this study. Impaired pain sensitivity thresholds were: (1) cold: 17.01°C, (2) heat: 43.91°C, and (3) mechanical: 4.42 g. Impaired cold pain sensitivity was the most common finding (63.6%), then heat (60%), and mechanical (38.2%). Impaired pain sensitivity to ≥1 testing modalities occurred in 81.8% of SCD patients. Determining impaired pain sensitivity thresholds increases clinical utility of QST. QST could be a screening tool to phenotype SCD pain, an outcome for pain interventional trials, or guide pain neurobiology investigations.

State of the art in biobehavioral approaches to the management of chronic pain in childhood

Chronic pain in childhood is prevalent, persistent and significantly impactful on most domains of life. The chronic pain experience occurs within a complex biopsychosocial framework, with particular emphasis on the social context. Currently, psychological treatments involve a cognitive-behavioral therapy treatment plan, providing some combination of psychoeducation, self-regulation training, maladaptive cognition identification, behavioral exposure and parent involvement. New treatment areas are emerging, such as group- and internet-based cognitive-behavioral therapy, motivational interviewing, comorbid obesity intervention and intensive multidisciplinary rehabilitation. Preliminary studies of emerging treatments demonstrate encouraging results; however, treatment effectiveness hinges on accurate matching of patient to treatment modality. Overall, the current direction of the field promises many innovative breakthroughs to ameliorate suffering in youth with chronic pain.

Early insights into the neurobiology of pain in sickle cell disease: A systematic review of the literature

Novel insights into the neurobiology of sickle cell disease (SCD) pain have recently been discovered. We systematically reviewed the literature focusing on original research that examined the biology of pain in SCD and/or addressed assessment or treatment of neuropathic pain in SCD. This review of 15 articles that met inclusion criteria provides epidemiological, basic, and clinical data that support central and/or peripheral nervous system abnormalities likely contribute to sickle cell pain. Continued basic and clinical investigation into pain neurobiology is imperative to translate these discoveries into novel ways to assess and treat neuropathic pain and decrease patient suffering.

Updated Mechanisms of Sickle Cell Disease-Associated Chronic pain

Sickle cell disease (SCD), a hemoglobinopathy, causes sickling of red blood cells, resulting in vessel blockage, stroke, anemia, inflammation, and extreme pain. A vast majority of SCD patients experience pain on a chronic basis, and many turn to opioids to provide limited relief. The side effects that come with chronic opioid use push for research into understanding the specific mechanisms of SCD-associated chronic pain. Current advances in SCD-associated pain have focused on alterations in the pain pathway including nociceptor sensitization and endogenous pain inducers. This article reviews the underlying pathophysiology of SCD, potential pain mechanisms, current treatments and their mechanism of action, and future directions of SCD-associated pain management. The information provided could help propel research in SCD-associated chronic pain and uncover novel treatment options for clinicians.