Facilitated Pronociceptive Pain Mechanisms in Radiating Back Pain Compared With Localized Back Pain

Correlations of The Central Sensitization Inventory, conditioned pain modulation, cognitions and psychological factors in individuals with chronic neck pain: A cross-sectional study

INTRODUCTION

Chronic neck pain (CNP) is a global public health problem, with high prevalence and absenteeism rates. Central sensitization (CS) as a basis for chronic pain may play an essential role in its development and progression. It is often comorbid with low conditioned pain modulation (CPM) effects, cognitions, and psychological problems.

OBJECTIVES

The purposes of this study were to (1) explore the relationship between pain-related cognitions and psychological factors, CPM effects, and the central sensitization inventory (CSI) scores; and (2) determine whether cognitions and psychological factors can predict CSI scores and CPM effects in individuals with CNP.

METHODS

Fifty-four individuals with CNP were recruited for this cross-sectional study. The following outcome measures were evaluated: The CSI (screening tool) was compared with the cold pressor test (CPT), which was the psychophysical test used to assess the CPM; neck pain intensity using the visual analogue scale (VAS), as well as pain-related cognitions (including kinesiophobia and pain catastrophization) and psychological states (including anxiety and depression) using self-report questionnaires.

RESULTS

CSI score was not associated with the CPM effect (r = 0.257, p > 0.05), and no cognitions or psychological factors were associated with CPM (p > 0.05), but CSI score was moderately positively correlated with kinesiophobia (r = 0.554, p < 0.01), lowly positively correlated with pain catastrophization (r = 0.332, p = 0.017) and anxiety (r = 0.492, p < 0.01), but not depression (r = 0.207, p = 0.132). Multiple linear regression analysis showed that kinesiophobia (B = 1.308, p < 0.01) and anxiety (B = 1.806, p = 0.02) were significant positive predictors of CSI score.

CONCLUSIONS

The findings confirm some of our hypotheses. Accordingly, the findings inferred that the CSI does not seem to respond to CPM effect in patients with CNP effectively. In addition, CSI score was associated with cognitions and psychological factors, of which kinesiophobia and anxiety were effective predictors. In clinical practice, pain-related cognitions and psychological factors should be fully considered to manage neck pain efficiently.

Conditioned pain modulation (CPM) paradigm type affects its sensitivity as a biomarker of fibromyalgia

Fibromyalgia (FM) is a widespread chronic pain syndrome, possibly associated with the presence of central dysfunction in descending pain inhibition pathways. Conditioned Pain Modulation (CPM) has been proposed as a biomarker of FM. Nonetheless, the wide variety of methods used to measure CPM has hampered robust conclusions being reached. To clarify the validity of CPM as a biomarker of FM, we tested two CPM paradigms (parallel and sequential) in a sample of 23 female patients and 23 healthy women by applying test (mechanical) stimuli and conditioning (pressure cuff) stimuli. We evaluated whether CPM indices could correctly classify patients and controls, and we also determined the correlations between the indices and clinical variables such as symptomatology, disease impact, depression, quality of life, pain intensity, pain interference, fatigue and numbness. In addition, we compared the clinical status of CPM responders (efficient pain inhibitory mechanism) and non-responders. We observed that only parallel CPM testing correctly classified about 70% of patients with FM. In addition, more than 80% of healthy participants were found to be responders, while the rate was about 50% in the FM patients. The sequential CPM test was not as sensitive, with a decrease of up to 40% in the response rate for both groups. On the other hand, we did not observe any correlation between CPM measures and clinical symptoms. In summary, our findings demonstrate the influence of the CPM paradigm used and confirm that CPM may be a useful marker to complement FM diagnosis. However, the findings also cast doubts on the sensitivity of CPM as a marker of pain severity in FM.

Conditioned pain modulation and psychological factors in young adults with recurrent or chronic neck pain

BACKGROUND

Controversy exists with the presence of alterations in descending pain inhibition mechanisms in patients with non-specific neck pain (NSNP). The aim of the present study was to evaluate the status of conditioned pain modulation CPM, remote pressure pain thresholds (PPT), and psychological factors in a specific subgroup of patients with NSNP such as young adult students. In addition, possible associations between CPM, psychological factors, and pain characteristics were analyzed.

METHODS

Thirty students with recurrent or chronic NSNP and 30 pain-free students were included in this cross-sectional study. The following measures were assessed: CPM, remote PPT, psychological factors (depression, anxiety, pain catastrophizing, and kinesiophobia), pain characteristics (duration, intensity, severity of chronic pain, interference with daily life), and central sensitization inventory (CSI).

RESULTS

No significant differences were found in the efficacy of CPM between students with chronic or recurrent NSNP and pain-free students (β coefficient = -0.67; 95% CI = -1.54, 0.20). However, students with pain showed a significantly higher remote PPT (mean difference = -1.94; 95% CI = -2.71, -1.18). and a greater presence of anxious (mean difference = 6; 95% CI = 2, 9) and depressive symptoms (mean difference = 8.57; 95% CI = 3.97, 13.16). In addition, significant moderate or strong correlations were found between CPM and pain intensity (partial r = 0.41), pain catastrophizing and mean pain intensity (r = 0.37), grade (r = 0.50), and interference of pain (r = 0.57), kinesiophobia and disability (r = 0.38), and depression and CSI (r = 0.39).

CONCLUSIONS

Young adult students with chronic or recurrent NSNP present remote hyperalgesia and symptoms of depression and anxiety but not dysfunctional CPM.

Is low back pain a risk/prognostic factor for the development and/or progression of temporomandibular disorders? A systematic review with meta-analysis

OBJECTIVES

To evaluate the association between low back pain (LBP) and painful temporomandibular disorders (TMDs).

METHODS

Systematic review of observational studies. Searches were conducted using OVID MEDLINE, CINHAL, Web of Science and PUBMED databases up to 21 October 2022. Qualitative and quantitative analyses were performed. Risk of bias (RoB) was assessed using the Quality in Prognosis Studies tool (QUIPS).

RESULTS

Eight studies were included in the present review with meta-analysis. The first onset of TMDs was more likely in patients with previous chronic LBP (hazard ratio (HR) 1.53 [95% confidence interval (CI): 1.28; 1.83, p < .00001]). In addition, patients with chronic LBP had 3.25 times the odds (OR) [95% CI: 1.94; 5.43, p < .00001] of having chronic TMDs than those who did not have chronic LBP. In addition, the higher the exposure to chronic LBP, the higher the risk of developing a first onset of TMDs.

CONCLUSIONS

Chronic LBP can be considered a risk/contributing factor for painful TMDs. Although there is a high certainty in the evidence linking chronic LBP with the risk of a first onset of TMDs, there are insufficient studies to draw definitive conclusions. Furthermore, while an association between chronic LBP and chronic TMDs and a dose-effect was observed between these two conditions, a limited number of studies and evidence exist to support these findings. Future studies are needed to increase the body of evidence.

Facilitated Central Pain Mechanisms Across the Menstrual Cycle in Dysmenorrhea and Enlarged Pain Distribution in Women With Longer Pain History

Dysmenorrhea (DYS), or recurrent menstrual pain, is a highly prevalent pain condition among otherwise healthy women. However, the progression of DYS over time and the influence of the menstrual cycle phases need to be better understood. While the location and distribution of pain have been used to assess pain mechanisms in other conditions, they are unexplored in DYS. Thirty otherwise healthy women with severe DYS and 30 healthy control women were recruited into 3 subgroups (n = 10) according to the length of their menstrual history (<5, 5-15, or>15 years since menarche). The intensity and distribution of menstrual pain were recorded. Pressure pain thresholds at abdominal, hip, and arm sites, pressure-induced pain distribution, temporal summation of pain, and pain intensity after pressure cessation over the gluteus medius were assessed at 3 menstrual cycle phases. Compared with the healthy control women, those with DYS showed lower pressure pain thresholds in every site and menstrual cycle phase (P < .05), enlarged pressure-induced pain areas during menstruations (P < .01), and increased temporal summation and pain intensity after pressure cessation in the overall menstrual cycle (P < .05). Additionally, these manifestations were enhanced during the menstrual and premenstrual phases compared to ovulation in women with DYS (P < .01). Women with long-term DYS demonstrated enlarged pressure-induced pain distribution, enlarged menstrual pain areas, and more days with severe menstrual pain compared to the short-term DYS subgroup (P < .01). Pressure-induced and menstrual pain distributions were strongly correlated (P < .001). These findings suggest that severe DYS is a progressive condition underscored by facilitated central pain mechanisms associated with pain recurrence and exacerbation. PERSPECTIVE: Enlarged pressure-induced pain areas occur in DYS, associated with the length of the condition and the distribution of menstrual pain. Generalized hyperalgesia is present throughout the entire menstrual cycle and intensifies during premenstrual and menstrual phases.

Pain-related cognitions and emotional distress are not associated with conditioned pain modulation: an explorative analysis of 1142 participants with acute, subacute, and chronic pain

ABSTRACT

Reduced conditioned pain modulation (CPM) and psychological distress co-occur frequently in many pain conditions. This study explored whether common negative pain cognitions and emotional factors were related to lower CPM in individuals across the spectrum from acute to chronic pain. Previously collected data on the CPM effect, pain-related cognitions (fear of movement, pain catastrophizing), and emotional distress (depression, anxiety) through questionnaires from 1142 individuals with acute, subacute, or chronic pain were used. The presence of negative psychological factors was dichotomized according to cutoff values for questionnaires. Associations between the presence of each negative psychological factor and the amplitude of pain reduction in the CPM paradigm was explored with Generalized Linear Models adjusted for sex, age, body mass index, and pain duration. A secondary analysis explored the cumulative effect of psychological factors on CPM. When dichotomized according to cutoff scores, 20% of participants were classified with anxiety, 19% with depression, 36% with pain catastrophizing, and 48% with fear of movement. The presence of any negative psychological factor or the cumulative sum of negative psychological factors was associated with lower CPM (individual factor: β between -0.15 and 0.11, P ≥ 0.08; total: β between -0.27 and -0.12, P ≥ 0.06). Despite the common observation of psychological factors and reduced CPM in musculoskeletal pain, these data challenge the assumption of a linear relationship between these variables across individuals with acute, subacute, and chronic pain. Arguably, there was a nonsignificant tendency for associations in nonexpected directions, which should be studied in a more homogenous population.

Increased Clinical Pain Locations and Pain Sensitivity in Women After Breast Cancer Surgery: Influence of Aromatase Inhibitor Therapy

OBJECTIVES

Aromatase inhibitors (AIs), which potently inhibit estrogen biosynthesis, are a standard treatment for hormone sensitive early-stage breast cancer. AIs have been associated with substantial joint pain and muscle stiffness (aromatase inhibitor-associated musculoskeletal syndrome). However, the link between AIs and number of clinical pain locations and pain sensitivity are less well understood. The aim of this study was to compare longitudinal changes in clinical pain and quantitative pain sensitivity between women who did or did not receive AI therapy.

METHODS

Women with early-stage breast cancer were prospectively enrolled and assessed for clinical pain in surgical and nonsurgical body areas using the Brief Pain Inventory and Breast Cancer Pain Questionnaire, and for pain sensitivity using quantitative sensory testing preoperatively and at 1 year postoperatively. Pain outcomes between participants who did and did not begin adjuvant AI therapy were compared using Wilcoxon Signed-Ranks and generalized estimating equation linear regression analyses.

RESULTS

Clinical pain and pain sensitivity were comparable between AI (n=49) and no-AI (n=106) groups preoperatively. After adjusting for body mass index, AI therapy was associated with a greater increase in the number of painful nonsurgical body sites (significant time by treatment interaction, P =0.024). Pain location was most frequent in knees (28%), lower back (26%), and ankles/feet (17%). Quantitative sensory testing revealed a significant decrease in pain sensitivity (increased pressure pain threshold) in the no-AI group over time, but not in the AI group.

CONCLUSIONS

AI therapy was associated with increased diffuse joint-related pain and greater post-treatment pain sensitivity, potentially implicating central sensitization as a contributing pain mechanism of aromatase inhibitor-associated musculoskeletal syndrome worthy of future investigation.

Not just sensitization: sympathetic mechanisms contribute to expand experimental referred pain

Background

Widespread pain partially depends upon sensitization of central pain mechanisms. However, mechanisms controlling pain distribution are not completely known. The present study sought to assess skin temperature variations in the area of experimentally-induced pain and potential sex differences.

Methods

Pressure-pain thresholds (PPTs) were measured on the right infraspinatus muscle. At the end of Day 0, all participants performed an eccentric exercise of the shoulder external rotators to induce muscle soreness 24 hours after. On Day 1, participants indicated on a body chart the area of pain induced by 60 seconds of suprathreshold pressure stimulation (STPS; PPT + 20%) on the right infraspinatus muscle. Skin temperature variations in the area of referred pain were recorded with an infrared thermography camera, immediately before and after the STPS.

Results

Twenty healthy, pain-free individuals (10 females) participated. On Day 0, the pre-STPS temperature was higher than the post-STPS temperature on the arm (P = 0.001) and forearm (P = 0.003). On Day 1, the pre-STPS temperature was higher than the post-STPS temperature on the shoulder (P = 0.015), arm (P = 0.001), and forearm (P = 0.010). On Day 0, the temperature decrease after STPS in females was greater than in males on the forearm (P = 0.039). On Day 1, a greater temperature decrease was found amongst females compared with males at the shoulder (P = 0.018), arm (P = 0.046), and forearm (P = 0.005).

Conclusions

These findings indicate that sympathetic vasomotor responses contribute to expand pressure-induced referred pain, especially among females.

Profiling and Association over Time between Disability and Pain Features in Patients with Chronic Nonspecific Neck Pain: A Longitudinal Study

OBJECTIVES

To longitudinally investigate the relationships between neck/arm disability and pain profile measures in individuals with chronic nonspecific neck pain (NSNP) at baseline, one month, and six months after a standardized physiotherapy intervention. A secondary aim was to compare pain sensitivity of individuals with chronic NSNP at baseline to healthy controls.

METHODS

A total of sixty-eight individuals with chronic NSNP and healthy controls were recruited. Neck disability index (NDI), the 11-item disabilities of the arm, shoulder, and hand questionnaire (QuickDASH), temporal summation (TS), pressure pain thresholds (PPTs), pain intensity and pain extent were assessed in individuals with chronic NSNP. For the cross-sectional assessment, TS and PPTs were compared to healthy controls.

RESULTS

After following a standardized physiotherapy intervention, local and distal PPTs to the neck region decreased at one and six month follow-ups, respectively. Pain extent decreased at one and six months. Furthermore, a positive correlation between neck/arm disability and pain intensity was found at baseline, whereas moderate positive correlations (e.g., between NDI and pain extent) at baseline, one and six month follow-ups and negative correlations at six months (e.g., between arm disability and PPTs) were found.

DISCUSSION

Overall, these findings indicate that pain sensitivity can worsen following treatment despite reduced pain extent and unchanged neck disability and pain intensity scores over a six-month period in individuals with chronic NSNP.

Neurophysiological and transcriptomic predictors of chronic low back pain: Study protocol for a longitudinal inception cohort study

Chronic low back pain is one of the most common, costly, and debilitating pain conditions worldwide. Increased mechanistic understanding of the transition from acute to chronic low back and identification of predictive biomarkers could enhance the clinical assessment performed by healthcare providers and enable the development of targeted treatment to prevent and/or better manage chronic low back pain. This study protocol was designed to identify the neurological and transcriptomic biomarkers predictive of chronic low back pain at low back pain onset. This is a prospective descriptive longitudinal inception cohort study that will follow 340 individuals with acute low back pain and 40 healthy controls over 2 years. To analyze the neurophysiological and transcriptomic biomarkers of low back pain, the protocol includes psychological and pain-related survey data that will be collected beginning within 6 weeks of low back pain onset (baseline, 6, 12, 24, 52 weeks, and 2 years) and remotely at five additional time points (8, 10, 16, 20 weeks, and 18 months). Quantitative sensory testing and collection of blood samples for RNA sequencing will occur during the six in-person visits. The study results will describe variations in the neurophysiological and transcriptomic profiles of healthy pain-free controls and individuals with low back pain who either recover to pain-free status or develop chronic low back pain.

Pain and Disability in Low Back Pain Can be Reduced Despite No Significant Improvements in Mechanistic Pain Biomarkers

OBJECTIVE

Altered balance in nociception in response to noxious stimuli is commonly reported in chronic low back pain (LBP). However, it is unclear whether an improvement in the clinical presentation is contingent on a reduction in pain sensitivity. This study investigated whether the quantitative sensory testing (QST) profile changes in people undergoing rehabilitation for LBP.

DESIGN

A prospective, observational case-control study.

METHODS

Forty males and females, 18 to 40 years' old (20 with LBP) participated in 2 sessions. QST was performed at baseline and after discharge from rehabilitation (LBP) or after 3 to 8 weeks (controls). The QST battery consisted of determining pressure-pain thresholds at the low back and shoulder, temporal summation of pain, and conditioned pain modulation. Questionnaire data was used to determine pain (Numeric Rating Scale [NRS]), disability (Roland-Morris Questionnaire [RMQ]), Fear Avoidance Beliefs (FABQ), and The Örebro Musculoskeletal Pain Screening Questionnaire (ÖMPSQ) at baseline and discharge. The treatment effect was determined by calculating the Cohen d.

RESULTS

No significant group×time interactions or main factor effect was found for any of the QST measures. The LBP group reported a significant reduction in NRS (P<0.0002, d=1.23), RMQ (P<0.0001, d=1.58), FABQ (P<0.001, d=0.87), and in the ÖMPSQ (P<0.00001, d=1.44).

CONCLUSIONS

The results indicate that an improvement of clinical LBP is not contingent upon changes in the pain sensory profile. The value of screening pain sensitivity in LBP patients in primary care, needs to be investigated further, due to the patient population heterogeneity and the sensitivity of assessment methods.

Methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system: a systematic review

ABSTRACT

Mechanism-based classification of pain has been advocated widely to aid tailoring of interventions for individuals experiencing persistent musculoskeletal pain. Three pain mechanism categories (PMCs) are defined by the International Association for the Study of Pain: nociceptive, neuropathic, and nociplastic pain. Discrimination between them remains challenging. This study aimed to build on a framework developed to converge the diverse literature of PMCs to systematically review methods purported to discriminate between them; synthesise and thematically analyse these methods to identify the convergence and divergence of opinion; and report validation, psychometric properties, and strengths/weaknesses of these methods. The search strategy identified articles discussing methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system. Studies that assessed the validity of methods to discriminate between categories were assessed for quality. Extraction and thematic analysis were undertaken on 184 articles. Data synthesis identified 200 methods in 5 themes: clinical examination, quantitative sensory testing, imaging, diagnostic and laboratory testing, and pain-type questionnaires. Few methods have been validated for discrimination between PMCs. There was general convergence but some disagreement regarding findings that discriminate between PMCs. A combination of features and methods, rather than a single method, was generally recommended to discriminate between PMCs. Two major limitations were identified: an overlap of findings of methods between categories due to mixed presentations and many methods considered discrimination between 2 PMCs but not others. The results of this review provide a foundation to refine methods to differentiate mechanisms for musculoskeletal pain.

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.

"Shooting pain" in lumbar radiculopathy and trigeminal neuralgia, and ideas concerning its neural substrates

Patients with radicular low back pain (radicular LBP, sciatica) frequently describe their pain as "shooting" or "radiating." The dictionary meaning of these words implies rapid movement, and indeed, many sufferers report feeling pain moving rapidly from the lower back or buttock into the leg. But, others do not. Moreover, the sensation of movement is paradoxical; it is neither predicted nor accounted for by current ideas about the pathophysiology of radicular LBP. We have used a structured questionnaire to evaluate the sensory qualities associated with "shooting" and "radiating" in 155 patients, 98 with radicular LBP and 57 with trigeminal neuralgia, a second chronic pain condition in which shooting/radiating are experienced. Results indicated a spectrum of different sensations in different people. Although many sciatica patients reported rapid downward movement of their pain, even more reported downward expansion of the area of pain, some reported upward movement, and for some, there was no spatial dynamic at all. The velocity of movement or expansion was also variable. By cross-referencing sensations experienced in the sciatica and trigeminal neuralgia cohorts with known signal processing modes in the somatosensory system, we propose testable hypotheses concerning the pathophysiology of the various vectorial sensations reported, their direction and velocity, and the structures in which they are generated. Systematic evaluation of qualitative features of "shooting" and "radiating" pain at the time of diagnosis can shed light on the pain mechanism in the individual patient and perhaps contribute to a better therapeutic outcomes.

Relationships Between Psychological, Social, Physical Activity, and Sleep Measures and Somatosensory Function in Individuals With Spinal Pain: A Systematic Review and Meta-analysis

OBJECTIVE

Somatosensory abnormalities are linked to clinical pain outcomes in individuals with spinal pain. However, a range of factors might confound the relationship between altered somatosensory function and clinical pain outcomes. This systematic review aimed to evaluate the literature to assess the level of evidence of associations between psychological, social, physical activity, and sleep measures and somatosensory function (assessed via sensory psychophysical testing) among individuals with spinal pain.

METHODS

A comprehensive literature search was performed in 6 electronic databases from their inception to June 2018. Two reviewers independently assessed the methodological quality using a modified Quality in Prognostic Studies (QUIPS) tool and supplemented with recommendations from the Critical Appraisal and Data Extraction for the Systematic Review of Prediction Modelling Studies (CHARMS) checklist and the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. The level of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) system. Data were pooled to evaluate the strength of the relationships of interest.

RESULTS

Among the 17 factors identified in the included studies, pain catastrophizing, depression, and pain-related fear have significant negative (small to fair) associations with pain thresholds. A "very low" to "moderate" quality of evidence was found for all the investigated factors. Subgroup analysis showed a smaller effect size for pain catastrophizing/fear of movement and pain thresholds in individuals with low back pain.

CONCLUSIONS

Psychological factors are associated negatively with pain thresholds and they need to be adjusted when establishing predictive relationships between somatosensory function and pain outcomes in individuals with spinal pain.

Local and Widespread Pressure Pain Hyperalgesia Is Not Side Specific in Females with Unilateral Neck Pain that Can Be Reproduced during Passive Neck Rotation

Current evidence for widespread hyperalgesia in non-specific neck pain (NSNP) is unclear. It is currently recommended to group NSNP patients according to pain-provoking movements. The aim of this study was to investigate local and widespread pain sensitivity in females with unilateral NSNP that is reproducible during passive neck rotation compared with matched controls, and to compare the side specific effect of pain location on pressure pain sensitivity among females with unilateral NSNP. Thirty-six females with unilateral NSNP evoked during passive ipsilateral (n = 20) or contralateral (n = 16) rotation toward the painful side were compared with 20 controls. Participants reported their pain intensity at rest and during passive neck rotation and completed the Neck Disability Index. Pressure pain thresholds (PPTs) were assessed bilaterally over the anterior scalene; the sternocleidomastoid; the levator scapulae; lateral to the spinous process of C6; the median, ulnar, and radial nerves; and the tibialis anterior. The ANOVA revealed lower PPTs in females with unilateral NSNP compared with the controls (all at p < 0.001), but no differences were found between the sides, nor was there any Group × side interaction. Among females with NSNP, those with higher pain intensity during ipsilateral rotation toward the painful side showed lower PPTs over the anterior scalene, median nerve, ulnar nerve, and tibialis anterior (all, p < 0.05) than females with higher pain intensity during contralateral rotation toward the painful side. These findings demonstrated bilateral local and widespread pressure pain hyperalgesia in females with unilateral NSNP that was reproducible during passive neck rotation compared with controls. There was no side specific effect of pain location on PPTs among females with unilateral NSNP.

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.

Cuff Pressure Algometry in Patients with Chronic Pain as Guidance for Circumferential Tissue Compression for Wearable Soft Exoskeletons: A Systematic Review

In this article, we report on a systematic review of the literature on pressure-pain thresholds induced and assessed by computerized cuff pressure algometry (CPA). The motivation for this review is to provide design guidance on pressure levels for wearable soft exoskeletons and similar wearable robotics devices. In our review, we focus on CPA studies of patients who are candidates for wearable soft exoskeletons, as pain-related physiological mechanisms reportedly differ significantly between healthy subjects and patients with chronic pain. The results indicate that circumferential limb compression in patients most likely becomes painful at ∼10-18 kPa and can become unbearable even below 25 kPa. The corresponding ranges for healthy control subjects are 20-42 kPa (painful limits) and 34-84 kPa (unbearable levels). In addition, the increase of pain with time tends to be significantly higher, and the adaptation to pain significantly lower, than in healthy subjects. The results of this review provide guidance to designers of wearable robotics for populations with chronic pain regarding rates and magnitudes of tissue compression that may be unacceptable to users.