Exercise-induced Hypoalgesia Is Impaired in Chronic Whiplash-associated Disorders (WAD) With Both Aerobic and Isometric Exercise

Exercise-induced hypoalgesia in chronic neck pain: A narrative review

Chronic neck pain (CNP) is a worldwide health problem with several risk factors. One of the most widely used treatments for managing this condition is therapeutic exercise, which could generate a response called exercise-induced hypoalgesia (EIH). There is no consensus on the best exercise modality to induce hypoalgesia. Therefore, this review aims to analyze and synthesize the state-of-the-art about the hypoalgesic effect of exercise in subjects with CNP. We included articles on EIH and CNP in patients older than 18 years, with pain for more than three months, where the EIH response was measured. Articles that studied CNP associated with comorbidities or measured the response to treatments other than exercise were excluded. The studies reviewed reported variable results. Exercise in healthy subjects has been shown to reduce indicators of pain sensitivity; however, in people with chronic pain, the response is variable. Some investigations reported adverse effects with increased pain intensity and decreased pain sensitivity, others found no clinical response, and some even reported EIH with decreased pain and increased sensitivity. EIH is an identifiable, stimulable, and helpful therapeutic response in people with pain. More research is still needed on subjects with CNP to clarify the protocols and therapeutic variables that facilitate the EIH phenomenon. In addition, it is necessary to deepen the knowledge of the intrinsic and extrinsic factors that influence EIH in people with CNP.

Conditioned Pain Modulation and Temporal Summation of Pain in Patients With Traumatic and Non-Specific Neck Pain: A Systematic Review and Meta-Analysis

In patients with neck pain, it is unclear whether pain inhibition and facilitation endogenous pain mechanisms are altered. This systematic review and meta-analysis aimed to improve their understanding by assessing conditioned pain modulation (CPM) and temporal summation of pain (TSP) in patients with neck pain associated with whiplash-associated disorders (WAD) or of a nonspecific neck pain (NSNP) nature compared to pain-free controls. Very low certainty evidence suggests: impaired CPM when assessed remotely in chronic WAD patients (n = 7, 230 patients and 204 controls, standardized mean differences (SMD) = -.47 [-.89 to -.04]; P = .04) but not locally (n = 6, 155 patients and 150 controls; SMD = -.34 [-.68 to .01]; P = .05), impaired CPM in chronic NSNP patients when assessed locally (n = 5, 223 patients and 162 controls; SMD = -.55 [-1.04 to -.06]; P = .04) but not remotely (n = 3, 72 patients and 66 controls; SMD = -.33 [-.92 to .25]; P = .13), TSP not facilitated in either chronic WAD (local TSP: n = 4, 90 patients and 87 controls; SMD = .68 [-.62 to 1.99]) (remote TSP: n = 8, 254 patients and 214 controls; SMD = .18 [-.12 to .48]) or chronic NSNP (local TSP: n = 2, 139 patients and 92 controls; SMD = .21 [-1.00 to 1.41]), (remote TSP: n = 3; 91 patients and 352 controls; SMD = .60 [-1.33 to 2.52]). The evidence is very uncertain whether CPM is impaired and TSP facilitated in patients with WAD and NSNP. PERSPECTIVE: This review and meta-analysis present the current evidence on CPM and TSP in patients with WAD and NSNP. Standardization of measurement methodology is needed to draw clear conclusions. Subsequently, future studies should investigate the clinical relevance of these measurements as prognostic variables or predictors of treatment success.

Exercise-Induced Hypoalgesia in Patients with Chronic Whiplash-Associated Disorders: Differences between Subgroups Based on the Central Sensitization Inventory

BACKGROUND

Physical exercise is an important element in the rehabilitation of chronic whiplash-associated disorders, with the physiological process underlying pain reduction called exercise-induced hypoalgesia. In chronic whiplash-associated disorders, exercise-induced hypoalgesia appears impaired, and the research suggests a relationship with symptoms of dysfunctional nociceptive processing, such as central sensitization. This study improves our understanding of exercise-induced hypoalgesia in chronic whiplash-associated disorders by examining the differences between the extent of exercise-induced hypoalgesia in subgroups based on scores on the central sensitization inventory (CSI).

METHODS

Data were collected from 135 participants with chronic whiplash-associated disorders who completed a set of questionnaires. Pain pressure thresholds and temporal summations were assessed before and after a submaximal aerobic bicycle exercise test.

RESULTS

We observed no interaction effect between exercise-induced hypoalgesia and the CSI scores for both pain pressure threshold and temporal summation. No overall statistical effect was measured in the analysis of the effect of time. The pain pressure threshold significantly related to the CSI. The temporal summation showed no correlation.

CONCLUSIONS

During this study, we did not find evidence for a difference in the presence of exercise-induced hypoalgesia when the subgroups were created based on the central sensitization cluster calculator. Limited evidence was found for the influence of CSI scores on the delta pain pressure threshold.

Reliability and measurement error of exercise-induced hypoalgesia in pain-free adults and adults with musculoskeletal pain: A systematic review

OBJECTIVES

We systematically reviewed the reliability and measurement error of exercise-induced hypoalgesia (EIH) in pain-free adults and in adults with musculoskeletal (MSK) pain.

METHODS

We searched EMBASE, PUBMED, SCOPUS, CINAHL, and PSYCINFO from inception to November 2021 (updated in February 2024). In addition, manual searches of the grey literature were conducted in March 2022, September 2023, and February 2024. The inclusion criteria were as follows: adults - pain-free and with MSK pain - a single bout of exercise (any type) combined with experimental pre-post pain tests, and assessment of the reliability and/or measurement error of EIH. Two independent reviewers selected the studies, assessed their Risk of Bias (RoB) with the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) RoB tool, and graded the individual results (COSMIN modified Grading of Recommendations Assessment, Development, and Evaluation).

RESULTS

We included five studies involving pain-free individuals (n = 168), which were deemed to have an overall "doubtful" RoB. No study including adults with MSK pain was found. The following ranges of parameters of reliability and measurement error of EIH were reported: intraclass correlation coefficients: 0-0.61; kappa: 0.01-0.46; standard error of measurement: 30.1-105 kPa and 10.4-21%; smallest detectable changes: 83.54-291.1 kPa and 28.83-58.21%.

CONCLUSIONS

We concluded, with a very low level of certainty, that the reliability and measurement error of EIH is, in pain-free adults, respectively, "insufficient" and "indeterminate." Future studies should focus on people with MSK pain and could consider using tailored exercises, other test modalities than pressure pain threshold, rater/assessor blinding, and strict control of the sources of variations (e.g., participants' expectations).

Longitudinal Changes and Associations Between Quantitative Sensory Testing and Psychological Factors in Whiplash-Associated Disorders: A Systematic Review and Meta-Analyses-Based Data Synthesis

Whiplash-associated disorders (WAD) represent a multifactorial condition often accompanied by altered nociceptive processing and psychological factors. This systematic review on acute and chronic WAD aimed to investigate the relationship between quantitative sensory testing (QST) and psychological factors and quantify whether their trajectories over time follow a similar pattern to disability levels. Eight databases were searched until October 2022. When 2 prospective studies examined the same QST or psychological variable, data synthesis was performed with random-effects meta-analysis by pooling within-group standardized mean differences from baseline to 3-, 6-, and 12-month follow-ups. From 5,754 studies, 49 comprising 3,825 WAD participants were eligible for the review and 14 for the data synthesis. Altered nociceptive processing in acute and chronic WAD, alongside worse scores on psychological factors, were identified. However, correlations between QST and psychological factors were heterogeneous and inconsistent. Furthermore, disability levels, some QST measures, and psychological factors followed general positive improvement over time, although there were differences in magnitude and temporal changes. These results may indicate that altered psychological factors and increased local pain sensitivity could play an important role in both acute and chronic WAD, although this does not exclude the potential influence of factors not explored in this review. PERSPECTIVE: Acute WAD show improvements in levels of disability and psychological factors before significant improvements in nociceptive processing are evident. Facilitated nociceptive processing might not be as important as psychological factors in chronic WAD-related disability, which indicates that chronic and acute WAD should not be considered the same entity although there are similarities. Nonetheless, pressure pain thresholds in the neck might be the most appropriate measure to monitor WAD progression.

Objectively and subjectively measured physical activity levels in individuals with whiplash associated disorder and aged-matched healthy controls

BACKGROUND

Whiplash associated disorders (WAD) are the most common non-hospitalised injuries resulting from a motor vehicle crash. Half of individuals with WAD experience ongoing pain and disability. Furthermore, individuals with persistent WAD have lower levels of aerobic capacity and isometric strength compared with age-matched controls. It is not known whether these differences are associated with increased levels of pain and disability, or with reduced physical activity (PA) participation.

OBJECTIVE

Our primary aim was to compare PA levels in individuals with persistent WAD with healthy controls. Secondary aims were to: compare objective and subjective measurements of PA; explore factors that may influence PA; and describe proportions of these populations meeting World Health Organisation PA guidelines.

METHODS

Objective (ActiGraph accelerometer; seven days) and subjective (International Physical Activity Questionnaire (IPAQ)) PA data were collected for n = 53 age-matched participants (WAD n = 28; controls n = 25).

RESULTS

Independent sample t-tests showed no significant difference in objectively measured PA (p>0.05) between WAD and controls. For the subjective measure (IPAQ), controls reported more overall weekly PA (t = 0.219, p<0.05), while WAD participants reported more weekly walking minutes (t = -0.712, p<0.05). Linear regression showed mental health quality-of-life predicted objectively measured moderate intensity PA (R2 = 0.225, F (2, 44) = 6.379, p<0.004) and subjectively reported overall PA (R2 = 0.132, F (1, 41) = 6.226, p<0.017). Bland-Altman analyses indicated that subjects over-reported MVPA and under-reported sedentary time using the IPAQ.

CONCLUSIONS

Individuals with WAD had levels of physical and mental health quality-of-life significantly lower than controls and below population norms yet participated in similar levels of PA. Given that increased perceptions of mental health quality-of-life were positively associated with objectively measured MVPA and subjectively reported overall PA, strategies to help people with WAD achieve adequate doses of MVPA may be beneficial. ActiGraph-measured and IPAQ-reported PA were discordant. Hence, IPAQ may not be a reliable measure of habitual PA in WAD.

Effect of exercise on chronic neck pain and central sensitization: A protocol for a randomized crossover trial

Exercise-induced hypoalgesia (EIH) has been found to vary widely within individuals with chronic neck pain (NP). Research has suggested that the presence of central sensitization within a subgroup of individuals with chronic NP might be a mediating factor to explain the relationship between exercise and improvements in patient-reported outcomes. Furthermore, recent work has found that lactate might play a role in the development and maintenance of chronic pain. The immediate effect of a single bout of physical exercise on central sensitization in individuals with chronic NP and the relationship between lactate concentration, central sensitization and pain sensitivity are to be investigated. Eighty adult participants with chronic NP will be recruited for this randomized crossover trial. Outcome measures, including temporal summation, conditioned pain modulation, EIH and lactate concentration, will be assessed before and after low- and high-intensity bicycling exercise. The outcomes of this study will provide new insights into the mechanistic effect of exercise on central sensitization in individuals with chronic NP and have the potential to add important information to the current exercise prescription guidelines for individuals with chronic NP. This study has been approved by the Human Research Ethics Committee, The University of Adelaide (H-2022-082) and registered in the Australian New Zealand Clinical Trials Registry (ACTRN12622000642785p).

Assessment of exercise-induced hypoalgesia in chronic low back pain and potential associations with psychological factors and central sensitization symptoms: A case-control study

INTRODUCTION

Exercise is the most recommended treatment for chronic low back pain (CLBP) and is effective in reducing pain, but the mechanisms underlying its effects remain poorly understood. Exercise-induced hypoalgesia (EIH) may play a role and is thought to be driven by central pain modulation mechanisms. However, EIH appears to be disrupted in many chronic pain conditions and its presence in people with CLBP remains unclear. As people suffering from chronic pain often exhibit psychological factors and central sensitization symptoms influencing pain perception, EIH might be associated with these factors.

OBJECTIVE

The aim of this study is to compare the level of EIH between participants with and without CLBP following back and wrist exercises and to assess the associations between EIH, psychological factors, and symptoms of central sensitization (using the central sensitization inventory - CSI) in CLBP.

METHOD

Twenty-eight participants with CLBP and 23 without pain were recruited. Pressure pain thresholds (PPT) were measured at 4 sites (2 bony sites = capitate, S1|2 muscle sites = wrist flexors, lumbar erector spinae) before and after each of two exercises (wrist flexion and lumbar extension). Exercise-induced hypoalgesia was defined as percent change in PPT from pre- to post-exercise. Participants with CLBP also completed questionnaires to measure psychological factors (e.g., kinesiophobia, catastrophizing, anxiety, and self-efficacy) and symptoms of central sensitization (CSI), and correlations with EIH were calculated.

RESULTS

After wrist exercise, EIH measured at the muscle sites was lower in the CLBP group compared with the pain-free group (p = 0.047) but no differences were found at bony sites (p = 0.49). No significant differences for EIH were observed following back exercise at muscle sites (p = 0.14) or at bony sites (p = 0.65). Exercise-induced hypoalgesia was not correlated with any psychological factors or with the CSI score.

CONCLUSION

The lower EIH following wrist exercises may represent an alteration in pain modulation control in CLBP. However, psychological factors and central sensitization symptoms may not explain the differences observed.

Exercise-induced hypoalgesic effects of different types of physical exercise in individuals with neck pain: A systematic review and meta-analysis

OBJECTIVE

To evaluate the exercise-induced hypoalgesic (EIH) effects of different types of physical exercise in individuals with neck pain.

DESIGN

Systematic review with meta-analysis.

LITERATURE SEARCH

An electronic search of six databases was completed to include studies assessing EIH effects on neck pain.

STUDY SELECTION CRITERIA

Randomized controlled trials, controlled trials, and observational studies that assessed before and immediate after-effects of a single session of physical exercise in people with neck pain were included. Two reviewers independently screened records, extracted outcomes, assessed the risk of bias, and rated the quality of evidence using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach.

DATA SYNTHESIS

EIH is characterized by increased pain threshold, pain tolerance, and/or decreased sensitivity to painful stimuli or unpleasantness, which may last up to 30 min after a single bout of exercise. EIH is usually measured with quantitative sensory testing (QST) and is mostly taken as the difference between pre- and postexercise pressure pain threshold (PPT). Data were pooled and analyzed using a fixed-effect meta-analysis.

RESULTS

Eleven articles were included in this review; nine with low risk of bias and two with some concerns about the risk of bias. Three studies with chronic whiplash-associated disorders (WAD) were included in the meta-analysis; isometric exercise had a larger EIH effect at the local testing site compared with submaximal aerobic exercises (MD = -0.21, [95% CI = -0.43, 0.00], p = 0.05, I²  = 92%), submaximal aerobic and isometric exercises had equal EIH effects at the remote testing site (MD = 0.01, [95% CI = -0.33, 0.35], p = 0.95, I²  = 0%), and submaximal aerobic exercises exerted comparably larger EIH effect at the remote testing site than local testing site (MD = -0.01, [95% CI = -0.20, 0.18], p = 0.93, I²  = 56%). The certainty of evidence (GRADE) for these analyses was low to very low. According to the descriptive analysis of the studies of chronic nonspecific neck pain, isometric and range of motion (ROM) exercises have shown EIH effects. Active stretching exercises have illustrated contradictory effects.

CONCLUSION

Isometric and ROM exercises exerted hypoalgesia at local and remote sites. A larger EIH effect following submaximal aerobic exercises was exerted at the remote testing site compared with the local site.

Training-induced hypoalgesia and its potential underlying mechanisms

It is well-established that a single bout of exercise can reduce pain sensitivity (i.e., exercise-induced hypoalgesia) in healthy individuals. However, exercise-induced hypoalgesia is often impaired in individuals with chronic pain. This might suggest that repeated bouts of exercise (i.e., exercise training) are needed in order to induce a reduction in pain sensitivity (i.e., training-induced hypoalgesia) among individuals with chronic pain, given that a single bout of exercise seems to be insufficient to alter pain. However, the effect of repeated bouts of exercise on pain sensitivity and its underlying mechanisms remain poorly understood. Therefore, the purpose of this review was to provide an overview of the existing literature on training-induced hypoalgesia, as well as discuss potential mechanisms of training-induced hypoalgesia and offer considerations for future research. Existing literature suggests that training interventions may induce hypoalgesic adaptations potentially driven by central nervous system and immune system factors. However, the limited number of randomized controlled trials available, along with the lack of understanding of underlying mechanisms, provides a rationale for future research.

Exercise-induced hypoalgesia after aerobic versus neck-specific exercise in people with acute/subacute whiplash-associated disorders: protocol for a randomised controlled trial

INTRODUCTION

A disturbance in exercise-induced hypoalgesia (EIH) has been observed in patients with chronic whiplash-associated disorders (WAD). Yet, no studies have examined whether EIH occurs in people with acute/subacute WAD. This study will determine whether EIH occurs immediately after and 24 hours after aerobic exercise (AE) and neck-specific exercise (NSE) in people with acute/subacute WAD.

METHODS AND ANALYSIS

A randomised controlled trial has been designed and is reported in line with the Standard Protocol Items: Recommendations for Interventional Trials. EIH will be assessed immediately after and 24 hours after AE, NSE and a control intervention (randomly allocated). As dependent variables of the study, we will measure pressure pain thresholds measured over the region of the spinous process of C2 and C5, the muscle belly of the tibialis anterior and over the three main peripheral nerve trunks, Neck Pain Intensity, Neck-Disability Index, Pain Catastrophizing Scale, Tampa Scale Kinesiophobia-11, self-reported Leeds Assessment of Neuropathic Symptoms and Signs Scale.

ETHICS APPROVAL AND DISSEMINATION

Ethical approval has been granted by the Ethics Committee from University Rey Juan Carlos (Madrid, Spain; reference number 0707202116721). The results of this study will be disseminated through presentations at scientific conferences and publication in scientific journals.

TRIAL REGISTRATION NUMBER

RBR-9tqr2jt, https://ensaiosclinicos.gov.br/observador/submissao/sumario/11551.

Associations between resting heart rate, resting blood pressure, psychological variables and pain processing in chronic whiplash-associated disorder: a cross-sectional study

Objective

Autonomic nervous system dysfunction has been implicated in chronic whiplash-associated disorder (WAD). However, the relationship between autonomic variables (e.g., resting heart rate and blood pressure) and clinical factors in chronic WAD is not well understood. This study sought to examine the associations between resting heart rate, resting blood pressure, pain processing and psychological variables in chronic WAD and in pain-free controls.

Design

Secondary analysis of a cross-sectional study.

Setting

University clinical research laboratory.

Subjects

Thirty-six people with chronic WAD Grade II (mean [SD] age 40.1 [14.6] years, 28 females) and 25 pain-free controls (35.6 [13.0] years, 17 females).

Methods

Participants had resting heart rate, systolic and diastolic blood pressure measured. Pain processing measures comprised: (i) pain pressure threshold at the cervical spine, hand and leg, (ii) temporal summation at the cervical spine and hand, and (iii) conditioned pain modulation. Psychological outcomes included measures of kinesiophobia, pain catastrophizing and post-traumatic stress symptoms. Correlations between autonomic variables, pain processing and psychological variables were determined (P < .05, 5% FDR).

Results

No significant correlations between autonomic and pain processing variables, or autonomic and psychological variables were found in the chronic WAD group. In the control group, diastolic blood pressure was positively correlated with cervical spine pressure pain threshold (r = 0.53, P = .007).

Conclusions

An association between blood pressure and pain sensitivity was observed in the control group but not the chronic WAD group. Such an association appears to be disrupted in chronic WAD, which may infer involvement of autonomic pathways in the pathophysiology of this condition.

The effect of prolonged experimental neck pain on exercise-induced hypoalgesia

ABSTRACT

Neck pain is a common musculoskeletal problem often accompanied by reduced exercise-induced hypoalgesia (EIH) or hyperalgesia compared to an asymptomatic population. This study investigated EIH in a healthy population during experimental neck pain. Forty participants were randomized into this double-blinded parallel-group study. On four separate test days (Day0, Day2, Day4, Day15), participants completed the Neck Disability Index (NDI) and scored neck pain intensity during head movements on a numerical rating scale (NRS). At the end of Day0 and Day2, Nerve Growth Factor (NGF) or isotonic saline (control) was injected into the right splenius capitis muscle. Pressure pain thresholds (PPTs) were recorded bilaterally over splenius capitis (neck), temporalis (head) and tibialis anterior (leg) muscles on all days. On Day0, Day4 and Day15, PPTs were recorded before and after a hand-bike exercise. EIH was defined as the PPT increase caused by the exercise. Compared with the control-group, the NGF-group demonstrated higher NDI scores at Day2 and Day4 (P<0.001,η2>0.557) and higher NRS scores (P<0.03,η2>0.09) along with reduced neck PPTs (P<0.01,d>0.44) at Day2(Right:95%CI[26.0,54.0];Left:95%CI[6.8,26.9]), Day4(Right:95%CI[40.5, 67.9];Left:95%CI[6.9,28.2]) and Day15(Right:95%CI[5.6,37.2];Left:95%CI[6.9,34.8]). Across days, the EIH-effect was reduced at the neck site in the NGF-group compared to the control-group (P<0.001,η2P=0.367,95%CI[-34.5,-13.7]). At the head and leg sites, the NGF-group showed reduced EIH-effect compared to the control-group (P<0.05,d>0.43) on Day4(Head:95%CI[-61.4,-22.9];Leg:95%CI[-154.7,-72.4]) and Day15(Head:95%CI[-54.3,-7.6];Leg:95%CI[-122.7,-34.4]). These results indicate that a few days of clinically comparable neck pain and hyperalgesia might have a negative impact on EIH-responses and may help explain why some neck pain patients do not experience immediate positive effects of exercise.

[Pain modulation through exercise : Exercise-induced hypoalgesia in physiotherapy]

Exercise prescription is a central tenet of physiotherapy. One of the numerous benefits of exercise is its influence on endogenous pain modulation. Exercise-induced hypoalgesia (EIH) refers to a short-term change in pain sensitivity following an acute bout of exercise. Interest in this phenomenon has grown considerably with over 150 articles published, including four systematic reviews in 2020 alone.This narrative review provides an overview of EIH including a definition and summary of the underlying mechanisms and mediating factors. Recent systematic reviews assessing EIH in people with and without musculoskeletal complaints were evaluated using AMSTAR2. Review findings confirm the presence of EIH. For asymptomatic people, confidence in the evidence was low to very low due to high heterogeneity of included studies, risk of bias, and study eligibility. For people with pain, there is very low confidence, at best, that subgroups or isometric exercise show altered EIH. Despite the growing body of evidence, challenges within the available evidence due to its complex nature are highlighted. Recommendations regarding outcome measures and exercise parameters are required, and further understanding of reliability and validity of EIH is needed. There is a demand to further elucidate these parameters and contextual factors to advance our understanding of EIH. Additional clinical research, especially in patient populations, is required to then provide implications for rehabilitation.

The descending pain modulation system predicts short term efficacy of multimodal pain therapy - an observational prospective cohort study

OBJECTIVES

Treating chronic pain patients with multimodal pain therapy (MMPT) alters perception, awareness, and processing of pain at multiple therapeutic levels. Several clinical observations suggest that the effects of therapy may go beyond the possible sum of each level of therapy and may be due to a central descending inhibitory effect measurable by conditioned pain modulation (CPM). Thus, we investigated whether CPM is able to identify a group of patients that benefit particularly from MMPT.

METHODS

This was an observational prospective cohort study. Patients were hospitalized on a special pain medicine ward with specially trained staff for 10 days. The patients were questioned and had investigations before and shortly after MMPT and were followed-up on 3 months post discharge. Before and after treatment, subjects were investigated via CPM and quantitative sensory testing (QST) as well as completing questionnaires. The study was registered in the German Clinical Trials Register (DRKS00006850).

RESULTS

During the study period of 24 months, 224 chronic pain patients were recruited. 51 percent of patients completed the study period. There was an improvement in overall groups regarding all domains assessed, lasting beyond the end of the intervention. Patients with a sufficient CPM effect, defined as a reduction in pain during the conditioning stimulus, at baseline did show a more pronounced reduction in mean pain ratings than those without. This was not the case 3 months after therapy. Furthermore, sufficient CPM was identified as a predictor for pain reduction using a linear regression model.

CONCLUSION

In conclusion, this study shows that while a heterogeneous group of patients with chronic pain disorders does sustainably benefit from MMPT in general, patients with a sufficient CPM effect do show a more pronounced decrease in pain ratings directly after therapy in comparison to those without.

Are Reports of Pain, Disability, Quality of Life, Psychological Factors, and Central Sensitization Related to Outcomes of Quantitative Sensory Testing in Patients Suffering From Chronic Whiplash Associated Disorders?

BACKGROUND

Chronic whiplash associated disorders (CWAD) are characterized by long-lasting symptoms of neck pain occurring after an acceleration-deceleration injury. Central sensitization (CS) has been suggested as the possible underlying mechanism for these symptoms, and is characterized by changes in the central nervous system. Besides CS, psychological factors are believed to play an important role in the experience of (chronic) pain.

OBJECTIVE

Investigating the relationships between self-reported pain, disability, quality of life, psychological factors, and symptoms of CS; and electrical-based quantitative sensory testing (QST) outcomes in CWAD patients. Secondly, to investigate the differences in QST between CWAD patients and pain-free controls.

METHODS

Seventy-two individuals with CWAD and 55 pain-free controls underwent electrical stimuli-based QST. Detection and pain thresholds (EPT), temporal summation (TS), and conditioned pain modulation were examined. Spearman correlation and linear mixed models analyses were performed to assess, respectively, the hypothesized associations and group differences in QST.

RESULTS

The Pain Catastrophizing magnification subscale correlated with the left wrist EPT (r=-0.332; P=0.004), and the Pain Anxiety Symptom Scale-20 with the left wrist (r=-0.325; P=0.005) and ankle (r=-0.330; P=0.005) EPT. TS at the ankle correlated with the CS inventory (r=0.303; P=0.010), Short Form 36 pain subscale (r=-0.325; P=0.005), and Illness Perception Questionnaire revised consequences subscale (r=0.325; P=0.005). EPTs left (P=0.011) and right wrist (P=0.023) were lower in the CWAD group, but conditioned pain modulation and TS did not differ between groups.

CONCLUSION

QST outcomes relate to psychological constructs, rather than to self-reported pain intensity and distribution. Local hyperalgesia was found in individuals with CWAD, but no differences in endogenous pain facilitation nor inhibition.

Heightened pain facilitation rather than impaired pain inhibition distinguishes those with moderate/severe disability in work-related neck pain

ABSTRACT

To better understand the mechanisms underpinning work-related neck pain, this cross-sectional and single-blinded study compared somatosensory profiles among sonographers with varied neck disability levels. Based on K-mean cluster analysis of scores on the neck disability index (NDI), participants were classified into no (NDI ≤ 8%, n = 31, reference group), mild (NDI = 10%-20%, n = 43), or moderate/severe (NDI ≥ 22%, n = 18) disability groups. Data were collected on bodily pain distribution and severity and psychological measures including depression, anxiety, pain-catastrophizing, and fear-avoidance beliefs using validated scales. Participants attended 1 session of quantitative sensory testing performed according to a standardized protocol, including local and remote thermal and mechanical pain thresholds, temporal summation of pain (TSP), conditioned pain modulation, and an exercise-induced analgesia paradigm. Compared with participants with no and mild disability, those with moderate/severe disability showed more widespread pain, cold and mechanical hyperalgesia at a remote nonpainful site, and significantly higher TSP. Participants with mild disability demonstrated significantly higher TSP than those with no disability. These group differences were attenuated after adjusting for depression or anxiety, indicating these psychological factors may mediate the somatosensory changes associated with neck disability. Group differences were not found for conditioned pain modulation or exercise-induced analgesia. These findings suggest that heightened pain facilitation, rather than impaired pain inhibition may underpin nociplastic pain in participants with moderate/severe disability, and it may be associated with depression and anxiety. Clinicians should be aware that individuals with work-related neck pain presenting with moderate/severe disability display distinct somatosensory features and tailor management strategies accordingly.