Pro-nociceptive and anti-nociceptive effects of a conditioned pain modulation protocol in participants with chronic low back pain and healthy control subjects

Mechanical and thermal thresholds before and after application of a conditioning stimulus in healthy Göttingen Minipigs

Minipigs are widely used in biomedical research for translational studies. However, information about pain elicited by experimental procedures is lacking. Non-invasive methods as quantitative sensory testing and conditioned pain modulation are particularly attractive. Our overarching aim was to explore and refine these methods for assessing post-operative pain in minipigs after myocardial infarction. As first step, we aimed at defining mechanical and thermal thresholds in healthy adults Göttingen Minipigs, evaluating their reliability, and testing their modifications after the application of a conditioning stimulus. Thresholds were assessed at different body sites before and after a painful conditioning stimulus (CS) (cuffed tourniquet) and sham CS (uncuffed tourniquet) in eleven animals. Thresholds' reliability was assessed using interclass correlation coefficient (ICC). The effect of the CS was assessed calculating absolute change, percentage change of the thresholds and standard error of measurement. Baseline mechanical thresholds (Newton) were: left hindlimb 81 [73; 81]; left forearm 81 [72.1; 81]; right forearm 81 [76; 81]; left chest 80.5 [68; 81]; right chest 81 [76.5; 81]; left neck 81 [70.3; 81]; right neck 74.8 [62.3; 80.5]. Reliability of mechanical thresholds was good at right chest (ICC = 0.835) and moderate at left chest (ICC = 0.591), left hindlimb (ICC = 0.606) and left neck (ICC = 0.518). Thermal thresholds showed poor reliability in all the tested sites. A modulatory effect was present at right chest, but it was seen when both a painful CS and a sham CS was applied. Minipigs tendentially showed a pro-nociceptive profile (i.e. conditioning pain facilitation). The measured thresholds are a reference for future trials in this species. Mechanical thresholds showed to be more reliable and, therefore, more useful, than thermal ones. The pain facilitation might be explained by the phenomenon of stress induced hyperalgesia, but this finding needs to be further investigated with a stricter paradigm.

Is the Central Sensitization Inventory (CSI) associated with quantitative sensory testing (QST)? A systematic review and meta-analysis

Central sensitization (CS) involves an amplification of neural processing within the central nervous system that can result in widespread pain patterns and hypersensitivity to stimuli. The Central Sensitization Inventory (CSI) and various quantitative sensory testing (QST) methods purport to assess clinical markers of CS. The purpose of this systematic review and meta-analysis was to summarize and quantify the associations between total CSI scores and QST measures from previous studies. A systematic search identified 39 unique studies that were deemed eligible for the systematic review and 33 studies for meta-analyses (with 3314 subjects and 154 effect sizes), including five QST modalities: conditioned pain modulation, temporal summation, pressure pain threshold, heat pain threshold, and cold pain threshold. The meta-analysis yielded statistically significant CSI-QST correlations in total subject samples for all five QST modalities. The strongest associations were identified between CSI scores and pain threshold testing, especially pressure pain threshold, in which 51% of effects sizes, from 29 studies and 3071 subjects, were determined to be in a medium to large range.

Conditioned pain modulation, kinesiophobia, and pain catastrophizing as prognostic factors for chronicity in a population with acute low back pain: An exploratory prospective study

BACKGROUND

Psychosocial factors and alteration of the somatosensory functions have been associated with persistent low back pain (LBP). A decreased capacity of the central nervous system to modulate pain has been suggested as a potential contributor to the persistence of pain.

OBJECTIVE

To investigate whether conditioned pain modulation (CPM), initial symptoms/disability, kinesiophobia, and pain catastrophizing is associated with the transition from acute to chronic LBP.

DESIGN

Prospective cohort study.

METHOD

Fifty participants presenting with acute LBP (<6 weeks) took part in three evaluation sessions (baseline, 3 and 6 months). At baseline and 3-month evaluations, all participants completed self-administered questionnaires (Oswestry Disability Index [ODI], Short Form of Brief Pain Inventory [BPI-SF], Tampa Scale of Kinesiophobia [TSK] and Pain Catastrophizing Scale [PCS]) and CPM was assessed. At the 6-month evaluation, questionnaires were readministered, and participants were dichotomized according to their status (Non-chronic LBP [NCLBP] or chronic LBP [CLBP]). Univariate tests were used to compare baseline variables between NCLBP and CLBP.

RESULTS

No significant baseline difference was found for TSK (p = 0.48), PCS (p = 0.78), CPM (p = 0.82), ODI (p = 0.78), BPI-SF severity (p = 0.50), and interference subscales (p = 0.54) between those categorized as NCLBP or CLBP at 6 months.

CONCLUSIONS

This exploratory study failed to support the hypothesis that inefficient CPM mechanisms and the presence of psychological factors could be factors associated with the transition to chronic pain in individuals with acute LBP.

Patients with neuropathic pain from lumbosacral radiculopathy demonstrate similar pressure pain thresholds and conditioned pain modulation to those with fibromyalgia

OBJECTIVE

The purpose of the study was to evaluate pain thresholds, impairment of the endogenous pain modulatory system, and self-reported cognitive-emotional and central sensitization-related symptoms among three subject groups: a rarely studied patient cohort with neuropathic pain from lumbosacral radiculopathy (NPLSR), patients with fibromyalgia (FM) and healthy controls (HC).

METHODS

Patient-reported pain-related symptomology was evaluated with psychometricallyvalidated questionnaires. Pressure pain threshold (PPT), heat pain threshold (HPT), and cold pain threshold (CPT) were assessed in the low back and contralateral forearm. Conditioned pain modulation (CPM) was evaluated with a recently introduced methodology that accounts for a standard error of measurement.

RESULTS

Compared to the HC subjects, the FM and NPLSR subjects had significantly lower pain thresholds and more CPM impairment. No significant differences in PPT and CPM were observed between the FM and NPLSR groups. Significant group differences were found in self-reported symptoms of depression, anxiety, stress, and central sensitization. Self-reported symptom severity increased in a stair-step fashion, with the HC group scoring lowest and FM group scoring highest.

CONCLUSION

The NPLSR group manifested CPM dysfunction and pressure hyperalgesia at similar levels to the FM group, indicating that these two chronic pain syndromes, likely based on different pathophysiological mechanisms, in fact share some common pain processing features. However, though both patient groups demonstrated similarities in pain processing, self-reported cognitive-emotional and central sensitization-related symptom severity was significantly higher in the FM cohort, which distinguished them from the chronic NPLSR cohort.

Effectiveness of motor control exercise, aerobic walking, and muscle strengthening programs in improving outcomes in a subgroup of population with chronic low back pain positive for central sensitization: a study protocol for a randomized controlled trial

BACKGROUND

The role of pain sensitivity in the development and maintenance of chronic pain states, impaired executive functioning, and patient recovery is being investigated. Conditioned pain modulation (CPM) is widely used to measure musculoskeletal pain associated with central sensitization (CS). Despite the recommendations of many reviews and clinical practice guidelines that exercise programs reduce pain and disability, the overall confidence in these results is considered "critically low." The "active ingredient" of exercise programs and the dominant factor influencing CPM remain largely unknown. The objectives of this trial are to determine: • If different exercises cause different results on the CPM in a subgroup of people with chronic low back pain (CLBP) who are labeled as having CS pain, • If a program of exercise interventions for 12 weeks would alter executive functioning, quality of life (QoL), disability, and pain in persons with CLBP. • The relationship between patient characteristics, executive functions, CPM, and QoL METHODS: The trial is a randomized, controlled, multi-center study with four experimental groups and one healthy control group. Both the researchers and the people in the study will be blinded to the results. This paper describes the protocol for a trial examining the effects of 12-week individualized, twice-weekly exercise sessions lasting 30 to 60 min in persons with CLBP, who are positive for CS. Participants will be randomized to receive either patient education with motor control exercises (MCE), superficial strengthening (SS), aerobic exercises (AE), or patient education alone. Another group comprised of healthy volunteers will serve as controls. The primary outcomes are changes in CPM outcomes as measured by the cold pressor test (CPT). The secondary objectives are to evaluate executive functioning, pain, disability, quality of life, and spine muscle strength. The outcomes will be measured at 3 months and at a 6-month follow-up.

DISCUSSION

The outcomes of the study will help in gaining more information and evidence about exercise-induced analgesia from the perspective of CPM. Measuring exercise outcomes will aid in scientifically prescribing exercise prescriptions in people with CLBP. The study outcomes will also assist in identifying the characteristics of individuals who will respond or respond indifferently to exercises. Investigating the relationship between the study's various outcomes could provide information for future trials.

TRIAL REGISTRATION

Clinical Trials Registry of India (CTRI) identifier: CTRI/2022/03/041143. Registered on 16 March 2022.

Human assumed central sensitization in people with acute non-specific low back pain: A cross-sectional study of the association with brain-derived neurotrophic factor, clinical, psychological and demographic factors

BACKGROUND

Early evidence suggests human assumed central sensitization (HACS) is present in some people with acute low back pain (LBP). Factors influencing individual variation in HACS during acute LBP have not been fully explored. We aimed to examine the evidence for HACS in acute LBP and the contribution of brain-derived neurotrophic factor (BDNF), clinical, psychological and demographic factors to HACS.

METHODS

Participants with acute LBP (<6 weeks after pain onset, N = 118) and pain-free controls (N = 57) from a longitudinal trial were included. Quantitative sensory testing including pressure and heat pain thresholds and conditioned pain modulation, BDNF serum concentration and genotype and questionnaires were assessed.

RESULTS

There were no signs of HACS during acute LBP at group level when compared with controls. Sensory measures did not differ when compared between controls and LBP participants with different BDNF genotypes. Two LBP subgroups with distinct sensory profiles were identified. Although one subgroup (N = 60) demonstrated features of HACS including pressure/heat pain hypersensitivity at a remote site and deficient conditioned pain modulation, pain severity and disability did not differ between the two subgroups. Variation in sensory measures (~33%) was partially explained by BDNF genotype, sex, age and psychological factors.

CONCLUSIONS

This study confirms that HACS is present in some people with acute LBP, but this was not associated with pain or disability. Further, no relationship was observed between BDNF and HACS in acute LBP. More research is needed to understand factors contributing to individual variation in sensory measures in LBP.

SIGNIFICANCE

Human assumed central sensitization (HACS) is present in acute low back pain (LBP) but factors contributing to individual variation are not fully explored. This study investigated the relationship between factors such as brain derived neurotrophic factor (BDNF) and HACS in acute LBP. Our findings indicate that HACS was present in specific LBP subgroups but BDNF was unrelated to HACS. Combinations of BDNF genotype, demographic and psychological factors explained a small proportion of the variation in sensory measures during acute LBP.

Efficiency of pain inhibition and facilitation of fibromyalgia patients is not different from healthy controls: Relevance of sensitivity-adjusted test stimuli

Background

Pain is a dynamic phenomenon dependent on the balance of endogenous excitatory and inhibitory systems, which can be characterized by quantitative sensory testing. Many previous studies of pain modulatory capacity of patients with fibromyalgia syndrome (FM) have reported decreased pain inhibition or increased pain facilitation. This is the first study to assess pain modulation, including conditioned pain modulation (CPM) and temporal pain summation, in the same healthy control (HC) and FM participants.

Methods

Only sensitivity-adjusted stimuli were utilized for testing of conditioned pain modulation (CPM) and temporal pain summation in 23 FM patients and 28 HC. All subjects received sensitivity-adjusted ramp-hold (sRH) during testing of pain facilitation (temporal summation) and pain inhibition (CPM). CPM efficacy was evaluated with test stimuli applied either concurrently or after application of the conditioning stimulus. Finally, the effects of CPM on pressure pain thresholds were tested.

Results

FM subjects required significantly less intense test and conditioning stimuli than HC participants to achieve standardized pain ratings of 50 ± 10 numerical rating scale (NRS) (p = 0.03). Using such stimuli, FM subjects' temporal pain summation and CPM efficacy was not significantly different from HC (all p > 0.05), suggesting similar pain facilitation and inhibition. Furthermore, the CPM efficacy of FM and HC participants was similar regardless of whether the test stimuli were applied during or after the conditioning stimulus (p > 0.05).

Conclusion

Similar to previous studies, FM participants demonstrated hyperalgesia to heat, cold, and mechanical stimuli. However, using only sensitivity-adjusted stimuli during CPM and temporal summation testing, FM patients demonstrated similarly effective pain inhibition and facilitation than HC, suggesting that their pain modulation is not abnormal.

The association between adverse childhood experiences and peripartal pain experience

ABSTRACT

Adverse childhood experiences (ACEs) are associated with altered ongoing and evoked pain experiences, which have scarcely been studied for the peripartum period. We aimed to investigate how ACEs affect pain experience in pregnancy and labor. For this noninterventional trial with a short-term follow-up, pregnant women were divided into a trauma group (TG) with ACEs (n = 84) and a control group (CG) without ACEs (n = 107) according to the Childhood Trauma Questionnaire. Pain experience in pregnancy and labor was recorded by self-report and the German Pain Perception Scale. Pain sensitivity prepartum and postpartum was assessed by Quantitative Sensory Testing and a paradigm of conditioned pain modulation (CPM), using pressure pain thresholds (PPTs) and a cold pressor test. The TG showed higher affective and sensory scores for back pain and a more than doubled prevalence of preexisting back pain. Pelvic pain differences were nonsignificant. The TG also exhibited increased affective scores (1.71 ± 0.15 vs 1.33 ± 0.11), but not sensory scores for labor pain during spontaneous delivery. There were no group differences in prepartum pain sensitivity. While PPTs increased through delivery in the CG (clinical CPM), and this PPT change was positively correlated with the experimental CPM (r = 0.55), this was not the case in the TG. The association of ACEs with increased peripartal pain affect and heightened risk for preexisting back pain suggest that such women deserve special care. The dissociation of impaired clinical CPM in women with ACEs and normal prepartum experimental CPM implies at least partly different mechanisms of these 2 manifestations of endogenous pain controls.

Sensitivity to movement-evoked pain, central sensitivity symptoms, and pro-nociceptive profiles in people with chronic shoulder pain: A parallel-group cross-sectional investigation

OBJECTIVE

To investigate whether sensitivity to movement-evoked pain (SMEP), central sensitivity symptom burden, and quantitative sensory testing (QST) outcomes differ between healthy controls and people with chronic shoulder pain.

METHODS

People with chronic shoulder pain (n = 39) and healthy controls (n = 26) completed validated questionnaires measuring demographic, pain characteristics, psychological factors, social support, sleep quality, central sensitivity inventory (CSI), and physical activity levels. A blinded assessor administered QST measuring pressure pain threshold, temporal summation, conditioned pain modulation, and cold hyperalgesia. All participants performed repeated lifting of weighted canisters and reported severity of pain over successive lifts of the weighted canisters. Between-group differences in the QST, SMEP and CSI scores were investigated. Demographic and psychosocial variables were adjusted in the analyses.

RESULTS

Dynamic mechanical allodynia, mechanical temporal summation, movement-evoked pain scores, SMEP index, and CSI scores were significantly (p ≤ 0.05) higher in the chronic shoulder pain group than in healthy controls. A significant proportion of people with chronic shoulder pain presented with pro-nociceptive profiles and experienced higher pain severity, interference, and disability.

CONCLUSIONS

People with chronic shoulder pain displayed symptoms and signs of central sensitization. Future research should investigate the predictive role of central sensitization on clinical outcomes in shoulder pain.

A feasibility study on yoga's mechanism of action for chronic low back pain: psychological and neurophysiological changes, including global gene expression and DNA methylation, following a yoga intervention for chronic low back pain

INTRODUCTION

Yoga has been shown to reduce pain and improve function in populations with chronic low back pain (cLBP), yet the underlying molecular mechanisms remain elusive. This study examined the feasibility and acceptability of a yoga research protocol, including recruitment, retention, and data collection, and investigated the preliminary effects of yoga on psychological and neurophysiological functions, including gene expression and DNA methylation profiles, in participants with cLBP.

METHODS

A one-arm trial was conducted with 11 participants with cLBP who enrolled in a 12-week yoga intervention. Data on subjective pain characteristics, quantitative sensory testing, and blood for analysis of differentially expressed genes and CpG methylation was collected prior to the start of the intervention and at study completion.

RESULTS

Based on pre-determined feasibility and acceptability criteria, the yoga intervention was found to be feasible and highly acceptable to participants. There was a reduction in pain severity, interference, and mechanical pain sensitivity post-yoga and an increase in emotion regulation and self-efficacy. No adverse reactions were reported. Differential expression analysis demonstrated that the yoga intervention induced increased expression of antisense genes, some of which serve as antisense to known pain genes. In addition, there were 33 differentially hypomethylated positions after yoga (log2 fold change ≥ 1), with enrichment of genes involved in NIK/NF-kB signaling, a major pathway that modulates immune function and inflammation.

DISCUSSION/CONCLUSIONS

The study supports the feasibility and acceptability of the proposed protocol to test a specific mechanism of action for yoga in individuals with cLBP. These results also support the notion that yoga may operate through our identified psychological and neurophysiologic pathways to influence reduced pain severity and interference.

Epigenome-wide DNA methylation profiling of conditioned pain modulation in individuals with non-specific chronic low back pain

BACKGROUND

The pathoanatomic cause of chronic low back pain (cLBP) cannot be identified for up to 90% of individuals. However, dysfunctional processing of endogenous nociceptive input, measured as conditioned pain modulation (CPM), has been associated with cLBP and may involve changes in neuronal gene expression. Epigenetic-induced changes such as DNA methylation (DNAm) have been associated with cLBP.

METHODS

In the present study, the relationship between CPM and DNAm changes in a sample of community-dwelling adults with nonspecific cLBP (n = 48) and pain-free controls (PFC; n = 50) was examined using reduced representation bisulfite sequencing. Gene ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were applied to identify key pathways involved in efficient versus deficient CPM.

RESULTS

Based on CPM efficiency, we identified 6006 and 18,305 differentially methylated CpG sites (DMCs) with q values < 0.01 among individuals with cLBP and PFCs, respectively. Most of the DMCs were hypomethylated and annotated to genes of relevance to pain, including OPRM1, ADRB2, CACNA2D3, GNA12, LPL, NAXD, and ASPHD1. In both cLBP and PFC groups, the DMCs annotated genes enriched many GO terms relevant to pain processing, including transcription regulation by RNA polymerase II, nervous system development, generation of neurons, neuron differentiation, and neurogenesis. Both groups also enriched the pathways involved in Rap1-signaling, cancer, and dopaminergic neurogenesis. However, MAPK-Ras signaling pathways were enriched in the cLBP, not the PFC group.

CONCLUSIONS

This is the first study to investigate the genome-scale DNA methylation profiles of CPM phenotype in adults with cLBP and PFCs. Based on CPM efficiency, fewer DMC enrichment pathways were unique to the cLBP than the PFCs group. Our results suggest that epigenetically induced modification of neuronal development/differentiation pathways may affect CPM efficiency, suggesting novel potential therapeutic targets for central sensitization. However, CPM efficiency and the experience of nonspecific cLBP may be independent. Further mechanistic studies are required to confirm the relationship between CPM, central sensitization, and nonspecific cLBP.

Exploring the relationship between meaningful conditioned pain modulation and stress system reactivity in healthy adults following exposure to the cold pressor task

BACKGROUND

The sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA) axis have been implicated in conditioned pain modulation (CPM). As there has recently been a push to identify meaningful CPM responses based on ± 2 SEM of the test stimulus, we sought to evaluate if meaningful CPM had relationships with both SNS and HPA axis reactivity.

METHODS

50 university-aged healthy participants (25 males, 25 females) underwent evaluation of pressure pain detection threshold (PPDT), conditioned pain modulation (CPM), galvanic skin response (GSR) and salivary cortisol before and after a cold pressor test (CPT). Meaningful CPM was evaluated based on change ±2 SEM of baseline PPDT to classify participants as experiencing inhibition of pain, facilitation, or non-response.

RESULTS

As a group, there were no significant changes in PPDT or salivary cortisol after exposure to noxious cold. GSR was significantly elevated from baseline values during the CPT, and 10 min after (p < 0.001). When meaningful CPM was assessed, only 30% of participants experienced inhibitory CPM. Within this group, there was a large positive correlation ranging from r = 0.63 to 0.69 (p < 0.01) between CPM and the absolute change in GSR from baseline to immersion, and the immediate 5 min after immersion.

CONCLUSIONS

This work continues to support the growing body of literature suggesting that CPM is not universally experienced. Inhibitory CPM may be associated with an increase in SNS activity for healthy participants in reaction to noxious cold. Future work is required to ascertain individual characteristics (e.g., age, sex) that relate to CPM responses.

No relevant differences in conditioned pain modulation effects between parallel and sequential test design. A cross-sectional observational study

Background

Conditioned pain modulation (CPM) is measured by comparing pain induced by a test stimulus with pain induced by the same test stimulus, either during (parallel design) or after (sequential design) the conditioning stimulus. Whether design, conditioning stimulus intensity and test stimulus selection affect CPM remains unclear.

Methods

CPM effects were evaluated in healthy participants (N = 89) at the neck, forearm and lower leg using the cold pressor test as the conditioning stimulus. In three separate experiments, we compared the impact of (1) design (sequential versus parallel), (2) conditioning stimulus intensity (VAS 40/100 versus VAS 60/100), and (3) test stimulus selection (single versus dual, i.e., mechanical and thermal). Statistical analyses of the main effect of design (adjusted for order) and experiment were conducted using linear mixed models with random intercepts.

Results

No significant differences were identified in absolute CPM data. In relative CPM data, a sequential design resulted in a slightly lower CPM effect compared to a parallel design, and only with a mechanical test stimulus at the neck (−6.1%; 95% CI [−10.1 to −2.1]) and lower leg (−5.9%; 95% CI [−11.7 to −0.1]) but not forearm (−4.5%; 95% CI [−9.0 to 0.1]). Conditioning stimulus intensity and test stimulus selection did not influence the CPM effect nor the difference in CPM effects derived from parallel versus sequential designs.

Conclusions

Differences in CPM effects between protocols were minimal or absent. A parallel design may lead to a minimally higher relative CPM effect when using a mechanical test stimulus. The conditioning stimulus intensities assessed in this study and performing two test stimuli did not substantially influence the differences between designs nor the magnitude of the CPM effect.

Pain Catastrophizing, Self-reported Disability, and Temporal Summation of Pain Predict Self-reported Pain in Low Back Pain Patients 12 Weeks After General Practitioner Consultation: A Prospective Cohort Study

OBJECTIVES

Patients with low back pain (LBP) often demonstrate pain sensitization, high degree of pain catastrophizing, and psychological distress. This study investigated whether pain sensitization mechanisms, the Pain Catastrophizing Scale (PCS), and Start Back Screening Tool were associated with pain in recurrent LBP patients 12 weeks after consulting their general practitioner (GP).

MATERIALS AND METHODS

In 45 LBP patients, pressure pain thresholds, temporal summation of pain (TSP), conditioned pain modulation (CPM), the Roland Morris Disability Questionnaire (RMDQ), and the PCS were assessed before consultation. Patients were classified into low to medium or high risk of poor prognosis on the basis of the Start Back Screening Tool. Worst pain within the last 24 hours was assessed on a visual analogue scale (VAS) at inclusion and 12 weeks after GP consultation.

RESULTS

VAS scores were reduced after 12 weeks in the low-to-medium (N=30, P<0.05), but not the high-risk group (N=15, P=0.40). RMDQ was reduced after 12 weeks (P<0.001), but with no difference between the groups. PCS was reduced in the low-to-medium and the high-risk group (P<0.05). TSP was significantly higher at follow-up in the high-risk group compared with the low-to-medium-risk group (P<0.05). A linear regression model explained 54.9% of the variance in VAS scores at follow-up utilizing baseline assessments of TSP, RMDQ, and PCS.

DISCUSSION

This study indicate that patients with LBP and high self-reported disability, high pain catastrophizing, and facilitated TSP assessed when consulting the GP might predictive poor pain progression 12 weeks after the consultation.

Do chronic low back pain subgroups derived from dynamic quantitative sensory testing exhibit differing multidimensional profiles?

OBJECTIVES

The relationship of pain sensitivity with pain and disability in low back pain (LBP) is complicated. It has been suggested increased understanding of dynamic quantitative sensory testing (QST) might be useful in increasing understanding of these relationships. This study aimed to create subgroups based on participant responses to dynamic QST, profile these subgroups based on multidimensional variables (including clinical measures of pain and disability, psychological and lifestyle variables and static QST), and investigate the association of subgroup membership with levels of pain intensity, LBP-related disability and disability risk at 12-month follow up.

METHODS

Participants (n=273) with dominant axial chronic non-specific LBP with duration of pain >3 months were included in this study. At baseline, eligible participants completed a self-report questionnaire to collect demographic, clinical, psychological and lifestyle data prior to dynamic and static QST. Dynamic QST measures were conditioned pain modulation (CPM) and temporal summation (TS). At 12-months follow up, clinical data were collected, including pain intensity and LBP-related disability. Sub-groups were formed by cross-tabulation. Analysis was undertaken to profile dynamic QST subgroup on demographic, clinical, psychological, lifestyle and static QST measures. Associations between dynamic QST subgroups and follow-up clinical variables were examined.

RESULTS

Based on dynamic QST, participants were allocated into four subgroups; normal CPM and normal TS (n=34, 12.5%); normal CPM and facilitated TS (n=6, 2.2%); impaired CPM and normal TS (n=186, 68.1%); impaired CPM and facilitated TS (n=47, 17.2%). At baseline no differences were demonstrated between subgroups across most clinical variables, or any psychological or lifestyle measures. The two subgroups with impaired CPM were more likely to have a higher number of painful body areas. Cold pain sensitivity was heightened in both the subgroups with facilitated TS. Subgroups did not differ across pain intensity, LBP-related disability and disability risk stratification at follow-up.

CONCLUSIONS

The profiles of people with axial LBP did not vary significantly across dynamic QST subgroups, save for those in groups with impaired CPM being more likely to have more widespread symptoms and those with facilitated TS having heightened cold pain sensitivity. Further, subgroup membership was not related to future pain and disability. The role of dynamic QST profiles in LBP remains unclear. Further work is required to understand the role of pain sensitivity in LBP. The utility of dynamic QST subgrouping might not be in determining of future disability. Future research might focus on treatment modifying effects of dynamic QST subgroups.

Test-retest reliability of pressure pain threshold and heat pain threshold as test stimuli for evaluation of conditioned pain modulation

OBJECTIVES

There is growing interest in conditioned pain modulation (CPM) protocols for evaluating the function of the descending pain-modulatory system in clinical settings. The aim of this study was to evaluate test-retest reliability of a CPM protocol with contact heat as a conditioning stimulus (CS) and two test stimuli (pressure pain threshold (PPT) and heat pain threshold (HPT)), all applied within one session. In addition, gender and age differences were evaluated.

METHODS

The study included 87 healthy subjects (average age 37.95 ± 12.02 years, 57.5% females). The magnitude of the results of the CPM test was calculated as the difference between subject-reported pain thresholds before and after application of the CS. To assess the reliability of the protocol, a subgroup of 66 subjects underwent re-test after 14±1 days. In order to investigate the influence of age on the CPM magnitude, subjects were divided into subgroups (20-29, 30-39, 40-49, 50-59 years).

RESULTS

The pain thresholds for both test stimuli (TS) were significantly higher following the application of the CS (p < 0.001). Values of the interclass correlation coefficient (ICC) for the CPM with PPT as the TS indicated good reliability (ICC=0.631, 95% CI:0.365-0.782), while those for the HPT indicated poor reliability (ICC=0.328, 95% CI:-0.067-0.582). Significant differences in CPM between genders were found for both TS. Significant CPM differences were not detected among the four age subgroups for either TS.

CONCLUSIONS

CPM effects can be successfully induced with both PPT and HPT as a TS, but PPT showed significantly higher reliability.

Pain referral area is reduced by remote pain

BACKGROUND

Endogenous pain inhibitory mechanisms are known to reduce pain intensity, but whether they influence the size and distribution of pain referral is unclear. This study aimed to determine if referred pain is reduced by applying a remote, conditioning painful stimulus.

METHODS

Twenty-four healthy men participated in this randomized, crossover study with a control and conditioning session. Referred pain was induced from the infraspinatus muscle (dominant side) by a painful pressure for 60 s. When applying pressure, the intensity was adjusted to a local pain intensity of 7/10 on a numerical rating scale. In the conditioning session, tonic painful pressure was simultaneously applied to the non-dominant leg during induction of referred pain. The area of referred pain was drawn onto a digital body chart and size extracted for data analysis.

RESULTS

For the total group and in a subgroup with distinct patterns of referred pain (n = 15/24), the pain area perceived in the back and front+back was smaller during the conditioning compared with the control (p < 0.05). No significant difference was found between sessions in a subgroup only demonstrating local pain (n = 9/24).

CONCLUSIONS

Engaging the descending noxious inhibitory control reduced the size of pain areas predominately when distinct pain referral was present. Assuming a conditioning effect of descending inhibitory control acting on dorsal horn neurons, these findings may indicate that mechanisms underlying pain referral can be modulated by endogenous control. The findings may indicate that referred pain may be a useful proxy to evaluate sensitivity of central pain mechanisms as previously suggested.

SIGNIFICANCE

The current results indicate a link between endogenous inhibition and pain referral. Descending inhibitory control effects on pain referral support a spinal mechanism involved in pain referral. Future studies should investigate whether the spatial characteristics of referred pain (e.g. size, frequency of affected body regions and distribution away from the primary nociceptive stimulus) can useful to evaluate the efficiency of endogenous pain modulation.

Alterations in pronociceptive and antinociceptive mechanisms in patients with low back pain: a systematic review with meta-analysis

Altered pronociceptive and antinociceptive mechanisms are often implicated in painful conditions and have been increasingly studied over the past decade. For some painful conditions, alterations are well-established, but in populations with low back pain (LBP), there remains considerable debate whether these mechanisms are altered. The present systematic review aimed to address this issue by identifying studies assessing conditioned pain modulation (CPM) and/or temporal summation of pain (TSP) in patients with LBP, comparing with either a healthy control group or using a method with reference data available. Qualitative synthesis and quantitative meta-analysis of group differences were performed. For CPM and TSP, 20 and 29 original articles were eligible, with data for meta-analysis obtainable from 18 (1500 patients and 505 controls) and 27 (1507 patients and 1127 controls) studies, respectively. Most studies were of poor-to-fair quality with significant heterogeneity in study size, population, assessment methodology, and outcome. Nonetheless, CPM was impaired in patients with LBP compared with controls (standardized mean difference = -0.44 [-0.64 to -0.23], P < 0.001), and the magnitude of this impairment was related to pain chronicity (acute/recurrent vs chronic, P = 0.003), duration (RS = -0.62, P = 0.006), and severity (RS = -0.54, P = 0.02). Temporal summation of pain was facilitated in patients with LBP compared with controls (standardized mean difference = 0.50 [0.29-0.72], P < 0.001), and the magnitude of this facilitation was weakly related to pain severity (RS= 0.41, P = 0.04) and appeared to be influenced by test modality (P < 0.001). Impaired CPM and facilitated TSP were present in patients with LBP compared with controls, although the magnitude of differences was small which may direct future research on the clinical utility.

Electrical (Pain) Thresholds and Conditioned Pain Modulation in Patients with Low Back-Related Leg Pain and Patients with Failed Back Surgery Syndrome: A Cross-Sectional Pilot Study

OBJECTIVE

When evaluating sensory dysfunctions and pain mechanisms in patients with low back pain (LBP), a specific subgroup of patients with radicular symptoms is often excluded. Comparative studies that evaluate sensory sensitivity in patients with a dominant nociceptive and neuropathic pain component are rarely performed. Therefore, the goal of this study was to examine differences in electrical thresholds and conditioned pain modulation (CPM) between patients with low back-related leg pain (LBRLP) and patients with failed back surgery syndrome (FBSS).

DESIGN

Cross-sectional study.

SETTING

University Hospital Brussels.

SUBJECTS

Twenty-one patients with LBRLP and 21 patients with FBSS were included.

METHODS

Electrical detection thresholds (EDTs), electrical pain thresholds (EPTs), and CPM were evaluated on the symptomatic and nonsymptomatic sides. Within- and between-group differences were evaluated for all parameters.

RESULTS

No between-group differences were found for EDT and EPT at both sides. On the nonsymptomatic side, a significantly lower CPM effect was found in the FBSS group (P = 0.04). The only significant within-group difference was an increased EDT at the symptomatic side in patients with FBSS (P = 0.01).

CONCLUSIONS

LBP patients with a primary neuropathic pain component revealed altered detection sensitivity at the symptomatic side, without severe indications for altered nociceptive processing, compared with LBP patients without a dominant neuropathic pain component. Endogenous modulation is functioning in LBP patients, although it is possible that it might only be functioning partially in patients with a dominant neuropathic pain component.

Within-session test-retest reliability of pressure pain threshold and mechanical temporal summation in healthy subjects

Objective

To determine the absolute and relative intra-rater within-session test-retest reliability of pressure pain threshold (PPT) and mechanical temporal summation of pain (TSP) at the low back and the forearm in healthy participants and to test the influence of the number and sequence of measurements on reliability metrics.

Methods

In 24 participants, three PPT and TSP measures were assessed at four sites (2 at the low back, 2 at the forearm) in two blocks of measurements separated by 20 minutes. The standard error of measurement, the minimal detectable change (MDC) and the intraclass correlation coefficient (ICC) were investigated for five different sequences of measurements (e.g. measurement 1, 1–2, 1-2-3).

Results

The MDC for the group (MDC_gr) for PPT ranged from 28.71 to 50.56 kPa across the sites tested, whereas MDC_gr for TSP varied from 0.33 to 0.57 out of 10 (numeric scale). Almost all ICC showed an excellent relative reliability (between 0.80 and 0.97), except when only the first measurement was considered (moderate). Although minimal differences in absolute PPT reliability were present between the different sequences, in general, using only the first measurement increase measurement error. Three TSP measures reduced the measurement error.

Discussion

We established that two measurements of PPT and three of TSP reduced the measurement error and demonstrated an excellent relative reliability. Our results could be used in future pain research to confirm the presence of true hypo/hyperalgesia for paradigms such as conditioned pain modulation or exercise-induced hypoalgesia, indicated by a change exceeding the measurement variability.

Conditioned pain modulation-A comprehensive review

Conditioned pain modulation (CPM) is a centrally processed measure of the net effect of the descending pain pathway. This comprises both the facilitatory as well as the inhibitory effect. In the past, CPM or similar effects have been previously described using different terminologies such as diffuse noxious inhibitory control (DNIC), heterotopic noxious conditioning stimulation (HNCS) or endogenous analgesia (EA). A variety of patient-related factors such as age, gender, hormones, race, genetic and psychological factors have been thought to influence the CPM paradigms. CPM paradigms have also been associated with a wide range of methodological variables including the mode of application of the 'test' as well as the 'conditioning' stimuli. Despite all these variabilities, CPM seems to reliably lend itself to the pain modulation profile concept and could in future become one of the phenotypic biomarkers for pain and also a guide for mechanism-based treatment in chronic pain. Future research should focus on establishing consistent methodologies for measuring CPM and thereby enhancing the robustness of this emerging biomarker for pain.

Individual variability and sex differences in conditioned pain modulation and the impact of resilience, and conditioning stimulus pain unpleasantness and salience

Distinct pain experiences are shaped both by personal attributes and characteristics of noxious stimuli. An Individual's capacity for endogenous pain inhibition (reflected by conditioned pain modulation [CPM]), their resilience, and the pain unpleasantness and salience of painful stimuli can impact their pain perception. Here, we aimed to determine how individual variability in CPM relates to sex and resilience as personal attributes, and pain unpleasantness and salience of the CPM conditioning stimulus (CS). We evaluated CPM in 106 healthy participants (51 female and 55 male) based on the change in test stimulus pain applied concurrently with a painful CS, both delivered by painful heat. The CS reduced test stimulus pain in only half of the participants (CPM subgroup), but did not do so for the other half (no-CPM subgroup), many who exhibited pain facilitation. A regression model explained CPM effects after accounting for sex, resilience, CS pain unpleasantness and salience. In the CPM subgroup regression model, the CPM effect was positively related to CS pain unpleasantness, while the CPM effect was not related to any variable in the no-CPM subgroup model. Correlation analyses revealed that the CPM effect was anticorrelated with resilience in males with no-CPM. The CPM effect was correlated with CS pain unpleasantness in males with CPM and in females with no-CPM. The CPM effect and CS salience were correlated in the whole group more strongly than in the subgroups. These data reveal that the complexity of contributors to CPM variability include both personal attributes and attributes of the CS.

A novel clinical applicable bed-side tool for assessing conditioning pain modulation: proof-of-concept

Background and aims

In recent years, focus on assessing descending pain modulation or conditioning pain modulation (CPM) has emerged in patients with chronic pain. This requires reliable and simple to use bed-side tools to be applied in the clinic. The aim of the present pilot study was to develop and provide proof-of-concept of a simple clinically applicable bed-side tool for assessing CPM.

Methods

A group of 26 healthy volunteers participated in the experiment. Pressure pain thresholds (PPT) were assessed as test stimuli from the lower leg before, during and 5 min after delivering the conditioning tonic painful pressure stimulation. The tonic stimulus was delivered for 2 min by a custom-made spring-loaded finger pressure device applying a fixed pressure (2.2 kg) to the index finger nail. The pain intensity provoked by the tonic stimulus was continuously recorded on a 0–10 cm Visual Analog Scale (VAS).

Results

The median tonic pain stimulus intensity was 6.7 cm (interquartile range: 4.6–8.4 cm) on the 10 cm VAS. The mean PPT increased significantly (P = 0.034) by 55 ± 126 kPa from 518 ± 173 kPa before to 573 ± 228 kPa during conditioning stimulation. When analyzing the individual CPM responses (increases in PPT), a distribution of positive and negative CPM responders was observed with 69% of the individuals classified as positive CPM responders (increased PPTs = anti-nociceptive) and the rest as negative CPM responders (no or decreased PPTs = Pro-nociceptive). This particular responder distribution explains the large variation in the averaged CPM responses observed in many CPM studies. The strongest positive CPM response was an increase of 418 kPa and the strongest negative CPM response was a decrease of 140 kPa.

Conclusions

The present newly developed conditioning pain stimulator provides a simple, applicable tool for routine CPM assessment in clinical practice. Further, reporting averaged CPM effects should be replaced by categorizing volunteers/patients into anti-nociceptive and pro-nociceptive CPM groups.

Implications

The finger pressure device provided moderate-to-high pain intensities and was useful for inducing conditioning stimuli. Therefore, the finger pressure device could be a useful bed-side method for measuring CPM in clinical settings with limited time available. Future bed-side studies involving patient populations are warranted to determine the usefulness of the method.

Pain inhibition is not affected by exercise-induced pain

Introduction:

Offset analgesia (OA) and conditioned pain modulation (CPM) are frequently used paradigms to assess the descending pain modulation system. Recently, it was shown that both paradigms are reduced in chronic pain, but the influence of acute pain has not yet been adequately examined.

Objectives:

The aim of this study is to investigate OA and CPM after exercise-induced pain to evaluate whether these tests can be influenced by delayed-onset muscle soreness (DOMS) at a local or remote body site.

Methods:

Forty-two healthy adults were invited to 3 separate examination days: a baseline appointment, the consecutive day, and 7 days later. Participants were randomly divided into a rest (n = 21) and an exercise group (n = 21). The latter performed a single intensive exercise for the lower back. Before, immediately after, and on the following examination days, OA and CPM were measured at the forearm and the lower back by blinded assessor.

Results:

The exercise provoked a moderate pain perception and a mild delayed-onset muscle soreness on the following day. Repeated-measurements analysis of variance showed no statistically significant main effect for either OA or CPM at the forearm or lower back (P > 0.05).

Conclusion:

Delayed-onset muscle soreness was shown to have no effect on the inhibitory pain modulation system neither locally (at the painful body part), nor remotely. Thus, OA and CPM are robust test paradigms that probably require more intense, different, or prolonged pain to be modulated.

AAPT Diagnostic Criteria for Chronic Low Back Pain

Chronic low back pain (CLBP) conditions are highly prevalent and constitute the leading cause of disability worldwide. The Analgesic, Anesthetic, and Addiction Clinical Trial Translations Innovations Opportunities and Networks (ACTTION) public-private partnership with the US Food and Drug Administration and the American Pain Society (APS), have combined to create the ACTTION-APS Pain Taxonomy (AAPT). The AAPT initiative convened a working group to develop diagnostic criteria for CLBP. The working group identified 3 distinct low back pain conditions which result in a vast public health burden across the lifespan. This article focuses on: 1) the axial predominant syndrome of chronic musculoskeletal low back pain, 2) the lateralized, distally-radiating syndrome of chronic lumbosacral radicular pain 3) and neurogenic claudication associated with lumbar spinal stenosis. This classification of CLBP is organized according to the AAPT multidimensional framework, specifically 1) core diagnostic criteria; 2) common features; 3) common medical and psychiatric comorbidities; 4) neurobiological, psychosocial, and functional consequences; and 5) putative neurobiological and psychosocial mechanisms, risk factors, and protective factors. PERSPECTIVE: An evidence-based classification of CLBP conditions was constructed for the AAPT initiative. This multidimensional diagnostic framework includes: 1) core diagnostic criteria; 2) common features; 3) medical and psychiatric comorbidities; 4) neurobiological, psychosocial, and functional consequences; and 5) putative neurobiological and psychosocial mechanisms, risk factors, and protective factors.

Pain Mechanisms in Low Back Pain: A Systematic Review With Meta-analysis of Mechanical Quantitative Sensory Testing Outcomes in People With Nonspecific Low Back Pain

BACKGROUND

Mechanical quantitative sensory testing (QST) assesses sensory functioning and detects functional changes in (central) nociceptive processing. It has been hypothesized that these functional changes might be apparent in people with nonspecific low back pain (LBP), although the results are mixed.

OBJECTIVE

The aim of this systematic review was to examine whether sensory function, measured with QST, was altered in people with nonspecific LBP.

METHODS

This systematic review was conducted according to PRISMA guidelines. Six databases were searched for relevant literature. Studies comparing mechanical QST measures involving people with subacute and chronic LBP and healthy controls were included if (1) pressure pain thresholds (PPTs), (2) temporal summation, or (3) conditioned pain modulation were reported. Risk of bias was assessed using the Newcastle-Ottawa scale. When possible, the results from different studies were pooled.

RESULTS

Twenty-four studies were included. Scores on the Newcastle-Ottawa scale varied between 1 and 6 points. People with nonspecific LBP, compared to healthy controls, had significantly lower PPTs at remote sites and increased temporal summation at the lower back. The PPTs measured at the scapula were significantly lower in patients with nonspecific LBP than in healthy controls (pooled mean difference, 119.2 kPa; 95% confidence interval: 91.8, 146.6 kPa; P<.001).

CONCLUSION

The PPT measurements at remote body parts were significantly lower in people with nonspecific LBP compared with healthy controls. Temporal summation and conditioned pain modulation measurements had mixed outcomes.

LEVEL OF EVIDENCE

Therapy, level 3a. J Orthop Sports Phys Ther 2019;49(10):698-715. Epub 23 Aug 2019. doi:10.2519/jospt.2019.8876.

Chronic low back pain is highly individualised: patterns of classification across three unidimensional subgrouping analyses

BACKGROUND AND AIMS

Chronic low back pain (CLBP) is a complex disorder where central and peripheral nociceptive processes are influenced by factors from multiple dimensions associated with CLBP (e.g. movement, pain sensitivity, psychological). To date, outcomes for treatments matched to unidimensional subgroups (e.g. psychologically-based) have been poor. Therefore, unidimensional subgrouping may not reflect the complexity of CLBP presentations at an individual level. The aim of this study was therefore to explore patterns of classification at an individual level across the three previously-published, data-driven, within-dimension subgrouping studies.

METHODS

Cross-sectional, multidimensional data was collected in 294 people with CLBP. Statistical derivation of subgroups within each of three clinically-important dimensions (pain sensitivity, psychological profile, pain responses following repeated spinal bending) was briefly reviewed. Patterns of classification membership were subsequently tabulated across the three dimensions.

RESULTS

Of 27 possible patterns across these dimensions, 26 were represented across the cohort.

CONCLUSIONS

This result highlights that while unidimensional subgrouping has been thought useful to guide treatment, it is unlikely to capture the full complexity of CLBP. The amount of complexity important for best patient outcomes is currently untested.

IMPLICATIONS

For clinicians this study highlights the high variability of presentations of people with CLBP at the level of the individual. For example, clinician's should not assume that those with high levels of pain sensitivity will also have high psychological distress and have pain summation following repeated spinal bending. A more flexible, multidimensional, clinically-reasoned approach to profile patient complexity may be required to inform individualised, patient-centred care. Such individualised care might improve treatment efficacy. This study also has implications for researchers; highlighting the inadequacy of unidimensional subgrouping processes and methodological difficulties in deriving subgroups across multidimensional data.

Divergent effects of conditioned pain modulation on subjective pain and nociceptive-related brain activity

BACKGROUND AND OBJECTIVES

Pain is a complex experience involving both nociceptive and affective-cognitive mechanisms. The present study evaluated whether modulation of pain perception, employing a conditioned pain modulation (CPM) paradigm, is paralleled by changes in contact heat-evoked potentials (CHEPs), a brain response to nociceptive stimuli.

METHODS

Participants were 25 healthy, pain-free, college students (12 males, 13 females, mean age 19.24 ± 0.97 years). Twenty computer-controlled heat stimuli were delivered to the non-dominant forearm and CHEPs were recorded at Cz using a 32-channel EEG system. After each stimulus, participants rated the intensity of the heat pain using the 0-100 numerical rating scale. The latency and amplitude of N2, P2 components as well as single-sweep spectral analysis of individual CHEPs were measured offline. For CPM, participants had to submerge their dominant foot into a neutral (32 °C) or noxious (0 °C) water bath. CHEPs and heat pain ratings were recorded in 3 different conditions: without CPM, after neutral CPM (32 °C) and after noxious CPM (0 °C).

RESULTS

The noxious CPM induced a facilitatory pain response (p = 0.001) with an increase in heat pain following noxious CPM compared to neutral CPM (p = 0.001) and no CPM (p = 0.001). Changes in CHEPs did not differ between conditions when measured as N2-P2 peak-to-peak amplitude (p = 0.33) but the CPM significantly suppressed the CHEPs-related delta power (p = 0.03). Changes in heat pain in the noxious CPM were predicted by trait catastrophizing variables (p = 0.04).

CONCLUSION

The current study revealed that pain facilitatory CPM is related to suppression of CHEPs delta power which could be related to dissociation between brain responses to noxious heat and pain perception.

STarT Back Tool risk stratification is associated with changes in movement profile and sensory discrimination in low back pain: A study of 290 patients

BACKGROUND

Investigation of movement and sensory profiles across STarT Back risk subgroups.

METHODS

A chronic low back pain cohort (n = 290) were classified as low, medium or high risk using the STarT Back Tool, and completed a repeated spinal bending task and quantitative sensory testing. Pain summation, time taken and the number of protective behaviours with repeated bending were measured. Sensory tests included two-point discrimination, temporal summation, pressure/thermal pain thresholds and conditioned pain modulation. Subgroups were profiled against movement and sensory variables.

RESULTS

The high-risk subgroup demonstrated greater pain summation following repeated forward bending (p < 0.001). The medium-risk subgroup demonstrated greater pain summation following repeated backward bending (p = 0.032). Medium- and high-risk subgroups demonstrated greater forward/backward bend time compared to the low-risk subgroup (p = 0.001, p = 0.005, respectively). Medium- and high-risk subgroups demonstrated a higher number of protective behaviours per forward bend compared to the low-risk subgroup (p = 0.008). For sensory variables, only two-point discrimination differed between subgroups, with medium- and high-risk subgroups demonstrating higher thresholds (p = 0.016).

CONCLUSIONS

This study showed altered movement characteristics and sensory discrimination across SBT risk subgroups in people with CLBP. Membership of the high SBT risk subgroup was associated with greater pain and disability levels, greater pain summation following repeated bending, slower bending times, a greater number of protective behaviours during forward bending, and a higher TPD threshold. Treatment outcomes for higher risk SBT subgroups may be enhanced by interventions specifically targeting movement and sensory alterations.

SIGNIFICANCE

In 290 people with chronic low back pain movement profile and two-point discrimination threshold differed across risk subgroups defined by the STarT Back Tool. Conversely, pain sensitivity did not differ across these subgroups. These findings may add further guidance for targeted care in these subgroups.

Alterations in Temporal Summation of Pain and Conditioned Pain Modulation Across an Episode of Experimental Exercise-Induced Low Back Pain

Persistent pain conditions, including low back pain (LBP), are often accompanied by alterations in pronociceptive and antinociceptive mechanisms, as quantified by temporal summation of pain (TSP) and conditioned pain modulation (CPM). It remains unclear whether altered pain sensitivity, CPM, and/or TSP are a consequence of pain presence or determine the degree of pain development. Pressure pain sensitivity, TSP, and CPM were assessed across an episode of exercise-induced LBP maintained for several days. Thirty healthy individuals participated in 3 experimental sessions: before (day 0), 2 days after fatiguing back muscle exercise with exercise-induced LBP present (day 2), and after pain resolution (day 7). Both handheld and cuff pressure-pain thresholds, along with TSP (10-cuff pain stimuli at .5 Hz) and CPM (cuff pain detection threshold prior versus during painful pressure conditioning) were assessed, alongside questionnaires pertaining to pain, disability, mood, sleep, menstruation, physical activity, and catastrophizing. The exercise-induced LBP model produced mild pain and disability, and reductions in pressure pain thresholds over both the lumbar and distant testing sites (p < .007). No pain-related changes were observed for TSP (p > .44) or CPM (p > .17). The baseline TSP was associated with the peak pain intensity of the exercise-induced LBP (p < .003). Perspective: Pressure-pain sensitivity was impacted by the presence of exercise-induced LBP, whereas TSP seemed to be more stable and was instead associated with the intensity of pain developed. No significant pain-related changes or associations were observed for CPM, suggesting this measure may have less usefulness in mild musculoskeletal pain conditions.

Predictors of disability and absenteeism in workers with non-specific low back pain: A longitudinal 15-month study

OBJECTIVES

The objective of this study was to identify baseline predictors of disability and absenteeism in workers with a history of non-specific low back pain (LBP).

METHODS

One hundred workers with a history of non-specific LBP participated in three evaluations (baseline, 7 and 15 months follow-up). Current and past history of LBP, clinical pain intensity, disability, absenteeism, fear-avoidance beliefs, pain catastrophizing, pain hypervigilance, work satisfaction and patient stratification based on "risk of poor clinical outcome assessment" (RPCO) were evaluated using questionnaires and interviews. In addition, cutaneous heat pain thresholds, cutaneous heat pain tolerance thresholds, conditioned pain modulation (CPM), trunk kinematics and muscle activity were measured during each evaluation. Logistic regression models were used to determine predictors of LBP disability and absenteeism at 15-months.

RESULTS

Sixty-eight workers returned for the 15-month follow-up and among this sample, 49% reported disability and 16% reported absenteeism at follow-up. Baseline clinical pain intensity predicted disability (OR = 1.08, 95%CI: 1.03-1.13) at 15-month while work satisfaction (OR = 0.93, 95%CI: 0.87-0.99) and RPCO (OR = 1.51, 95%CI: 1.05-2.16) predicted absenteeism. These results remained significant after adjustments for age, gender as well as type of work and intervention.

CONCLUSION

This study highlights the importance of clinical pain and psychological factors in the prediction and potentially the prevention of future disability. Screening tools assessing these risk factors can be useful to evaluate workers with past history of low back pain.

Individual Variation in Pain Sensitivity and Conditioned Pain Modulation in Acute Low Back Pain: Effect of Stimulus Type, Sleep, and Psychological and Lifestyle Factors

Generalized hyperalgesia and impaired pain modulation are reported in chronic low back pain (LBP). Few studies have tested whether these features are present in the acute phase. This study aimed to test for differences in pain presentation in early-acute LBP and evaluate the potential contribution of other factors to variation in sensitivity. Individuals within 2 weeks of onset of acute LBP (n = 126) and pain-free controls (n = 74) completed questionnaires related to their pain, disability, behavior, and psychological status before undergoing conditioned pain modulation (CPM) and pain threshold (heat, cold, and pressure) testing at the back and forearm/thumb. LBP participants were more sensitive to heat and cold at both sites and pressure at the back than controls, without differences in CPM. Only those with high-pain (numeric rating scale ≥4) were more sensitive to heat at the forearm and pressure at the back. Four subgroups with distinct features were identified: "high sensitivity," "low CPM efficacy," "high sensitivity/low CPM efficacy," and "low sensitivity/high CPM efficacy." Various factors such as sleep and alcohol were associated with each pain measure. Results provide evidence for generalized hyperalgesia in many, but not all, individuals during acute LBP, with variation accounted for by several factors. Specific pain phenotypes provide candidate features to test in longitudinal studies of LBP outcome.

PERSPECTIVE

Sensory changes indicative of increased/decreased central processing of pain and nociceptive input presented differently between individuals with acute LBP and were related to factors such as sleep and alcohol. This may underlie variation in outcome and suggest potential for early identification of individuals with poor long-term outcome.

From acute to persistent low back pain: a longitudinal investigation of somatosensory changes using quantitative sensory testing-an exploratory study

Introduction

Chronic low back pain (LBP) is commonly associated with generalised pain hypersensitivity. It is suggested that such somatosensory alterations are important determinants for the transition to persistent pain from an acute episode of LBP. Although cross-sectional research investigating somatosensory function in the acute stage is developing, no longitudinal studies designed to evaluate temporal changes have been published.

Objectives

This exploratory study aimed to investigate the temporal development of somatosensory changes from the acute stage of LBP to up to 4 months from onset.

Methods

Twenty-five people with acute LBP (<3 weeks' duration) and 48 pain-free controls were prospectively assessed at baseline using quantitative sensory testing with the assessor blinded to group allocation, and again at 2 and 4 months. Psychological variables were concurrently assessed. People with acute LBP were classified based on their average pain severity over the previous week at 4 months as recovered (≤1/10 numeric rating scale) or persistent (≥2/10 numeric rating scale) LBP.

Results

In the persistent LBP group, (1) there was a significant decrease in pressure pain threshold between 2 and 4 months (P < 0.013), and at 4 months, pressure pain threshold was significantly different from the recovered LBP group (P < 0.001); (2) a trend towards increased temporal summation was found at 2 months and 4 months, at which point it exceeded 2 SDs beyond the pain-free control reference value. Pain-related psychological variables were significantly higher in those with persistent LBP compared with the recovered LBP group at all time points (P < 0.05).

Conclusion

Changes in mechanical pain sensitivity occurring in the subacute stage warrant further longitudinal evaluation to better understand the role of somatosensory changes in the development of persistent LBP. Pain-related cognitions at baseline distinguished persistent from the recovered LBP groups, emphasizing the importance of concurrent evaluation of psychological contributors in acute LBP.

Convergent Validity of the Dutch Central Sensitization Inventory: Associations with Psychophysical Pain Measures, Quality of Life, Disability, and Pain Cognitions in Patients with Chronic Spinal Pain

OBJECTIVE

Symptoms of central sensitization (CS) have been described in patients with chronic spinal pain (CSP). Although a gold standard to diagnose CS is lacking, psychophysical pain measures are often used. The Central Sensitization Inventory (CSI) is proposed as an alternative method and indirect tool for the evaluation of CS symptomatology. The aim of the current study was to evaluate the convergent validity of the CSI by investigating the association with psychophysical pain measures and self-reported measures of current pain intensity, quality of life, disability, and catastrophizing in CSP patients.

METHODS

One hundred sixteen patients with nonspecific CSP were included in the present study. Patients completed the CSI, were subjected to pressure pain thresholds (PPTs) and a conditioned pain modulation (CPM) paradigm, and completed questionnaires for current pain intensity, quality of life, pain disability, and pain catastrophizing.

RESULTS

Higher CSI scores were weakly correlated with lower PPTs (-0.276 ≤ r ≤ -0.237; all P ≤ 0.01) and not with CPM efficacy (r = 0.017; P = 0.858). Higher CSI scores were moderately correlated with higher current pain intensity (r = 0.320; P < 0.001), strongly correlated with lower physical (r = -0.617; P < 0.001) and emotional (r = -0.635; P < 0.001) quality of life, and moderately correlated with higher pain disability (r = 0.472; P < 0.001) and higher pain catastrophizing (r = 0.464; P < 0.001).

CONCLUSION

The CSI was weakly associated with PPTs and not with CPM efficacy in CSP patients. Moderate to strong associations were found with current pain intensity, quality of life, disability, and catastrophizing. The current results illustrate that the CSI does not reflect a direct measure of CS, yet is a representation of general distress, possible originating from CS symptoms.

Assessment and manifestation of central sensitisation across different chronic pain conditions

Different neuroplastic processes can occur along the nociceptive pathways and may be important in the transition from acute to chronic pain and for diagnosis and development of optimal management strategies. The neuroplastic processes may result in gain (sensitisation) or loss (desensitisation) of function in relation to the incoming nociceptive signals. Such processes play important roles in chronic pain, and although the clinical manifestations differ across condition processes, they share some common mechanistic features. The fundamental understanding and quantitative assessment of particularly some of the central sensitisation mechanisms can be translated from preclinical studies into the clinic. The clinical perspectives are implementation of such novel information into diagnostics, mechanistic phenotyping, prevention, personalised treatment, and drug development. The aims of this paper are to introduce and discuss (1) some common fundamental central pain mechanisms, (2) how they may translate into the clinical signs and symptoms across different chronic pain conditions, (3) how to evaluate gain and loss of function using quantitative pain assessment tools, and (4) the implications for optimising prevention and management of pain. The chronic pain conditions selected for the paper are neuropathic pain in general, musculoskeletal pain (chronic low back pain and osteoarthritic pain in particular), and visceral pain (irritable bowel syndrome in particular). The translational mechanisms addressed are local and widespread sensitisation, central summation, and descending pain modulation.

Significance

Central sensitisation is an important manifestation involved in many different chronic pain conditions. Central sensitisation can be different to assess and evaluate as the manifestations vary from pain condition to pain condition. Understanding central sensitisation may promote better profiling and diagnosis of pain patients and development of new regimes for mechanism based therapy. Some of the mechanisms underlying central sensitisation can be translated from animals to humans providing new options in development of therapies and profiling drugs under development.

Pharmacokinetic and pharmacodynamic evaluation of oxycodone and naltrexone for the treatment of chronic lower back pain

INTRODUCTION

Chronic low back pain (CLBP) is a common and difficult illness to manage. Some individuals with CLBP have pain processing disorders and are also at risk for opioid abuse, misuse; addiction and diversion. Guidelines have been published to guide management; neuromodulation, exercise, mindfulness-based stress reduction and cognitive behavior therapies among other non-pharmacological reduce the pain of CLBP with minimal toxicity. Pharmacological management includes acetaminophen, NSAIDs and antidepressants, mainly duloxetine. Abuse-deterrent opioids have been developed which have been shown to reduce pain and opioid abuse risk. ALO-02 is a tamper-resistant sustained release opioid consisting of extended release oxycodone and sequestered naltrexone. Pivotal studies of ALO-02 have centered on patients with CLBP.

AREAS COVERED

This manuscript will review CLBP, the pivotal analgesic and clinical abuse potential studies of ALO-02. The opinion will cover whether opioids should be used for CLBP, when they should be used and opioid choices.

EXPERT OPINION

ALO-02 is one of several opioids which can be considered in the management of CLBP. The outcome to a trial of opioids should be function rather than analgesia. Most analgesic trials for CLBP have had analgesia as the primary outcome and function has not been vigorously studied as an outcome. Opioids should be considered as a trial only when other non-opioid analgesics have failed to improve analgesia and function. Universal precautions should be routinely part of phase III analgesic trial particularly for chronic non-malignant pain.