Experimental and Clinical Applications of Quantitative Sensory Testing Applied to Skin, Muscles and Viscera

The Potential Role of Sensory Testing, Skin Biopsy, and Functional Brain Imaging as Biomarkers in Chronic Pain Clinical Trials: IMMPACT Considerations

Valid and reliable biomarkers can play an important role in clinical trials as indicators of biological or pathogenic processes or as a signal of treatment response. Currently, there are no biomarkers for pain qualified by the U.S. Food and Drug Administration or the European Medicines Agency for use in clinical trials. This article summarizes an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting in which 3 potential biomarkers were discussed for use in the development of analgesic treatments: 1) sensory testing, 2) skin punch biopsy, and 3) brain imaging. The empirical evidence supporting the use of these tests is described within the context of the 4 categories of biomarkers: 1) diagnostic, 2) prognostic, 3) predictive, and 4) pharmacodynamic. Although sensory testing, skin punch biopsy, and brain imaging are promising tools for pain in clinical trials, additional evidence is needed to further support and standardize these tests for use as biomarkers in pain clinical trials.

PERSPECTIVE

The applicability of sensory testing, skin biopsy, and brain imaging as diagnostic, prognostic, predictive, and pharmacodynamic biomarkers for use in analgesic treatment trials is considered. Evidence in support of their use and outlining problems is presented, as well as a call for further standardization and demonstrations of validity and reliability.

Changes in Cytokines, Sensory Tests, and Self-reported Pain Levels After Manual Treatment of Low Back Pain

STUDY DESIGN

Unbalanced 3-factor design with repeated measures on 1 factor.

OBJECTIVE

To determine the effect of manual treatment (MT) on cytokine and pain sensations in those with and without low back pain (LBP).

SUMMARY OF BACKGROUND DATA

Evidence suggests that MT reduces LBP but by unknown mechanisms. Certain cytokines have been elevated in patients with LBP and may be affected by MT.

METHODS

Participants aged 20-60 years with chronic LBP or without LBP were recruited and randomly assigned to MT, sham ultrasound treatment, or no treatment groups. Venous blood samples were collected and pain levels assessed at baseline, 1 hour later, and 24 hours later. Blood was analyzed for interleukin (IL)-1β, IL-6, tumor necrosis factor-α, and C-reactive protein. Pain levels were measured by pressure pain threshold (PPT), mechanical detection threshold (MDT), dynamic mechanical allodynia, and self-report.

RESULTS

Forty (30 women, age 36±11 y) participants completed the study, 33 with LBP (13 MT, 13 sham ultrasound treatment, and 7 no treatment) and 7 without LBP. Participants with or without LBP could not be differentiated on the basis of serum cytokine levels, PPT, or MDT (P≥0.08). There were no significant differences between the groups at 1 hour or 24 hours on serum cytokines, PPT, or MDT (P≥0.07). There was a significant decrease from baseline in IL-6 for the no treatment (LBP) group (P=0.04), in C-reactive protein for the sham ultrasound treatment group (P=0.03), in MDT for all 3 LBP groups (P≤0.02), and in self-reported pain for the MT and sham ultrasound treatment groups (P=0.03 and 0.01).

CONCLUSIONS

Self-reported pain was reduced with MT and sham ultrasound treatment 24 hours after treatment, but inflammatory markers within venous circulation and quantitative sensory tests were unable to differentiate between study groups. Therefore, we were unable to characterize mechanisms underlying chronic LBP.

Association Between Borderline Personality Features and Temporal Summation of Second Pain: A Cross-Sectional Study

Individuals with greater borderline personality features may be vulnerable to chronic pain. Because pain is an unpleasant sensory and emotional experience, affect dysregulation as the core personality feature may be linked to pain hypersensitivity. Studies have found that greater borderline features are associated with increased intensity in clinical and experimental pain, and that depression mediates this increase. The current study further examined the association between borderline features and heat pain sensitivity, the contribution of affect dysregulation and the other borderline personality factors (identity problems, negative relationships, self-harming/impulsivity) to the association, and depression as a mediator. Additionally, we examined whether blunted sympathetic responses mediate the association between borderline features and temporal summation of second pain (TSSP). Thermal pain threshold, thermal TSSP and aftersensations pain were assessed in 79 healthy individuals with varying degrees of borderline features. TSSP is a proxy measure for central sensitization and refers to the gradual increase in pain to repeated nociceptive stimuli. A regression analysis showed that greater borderline features predicted greater TSSP (β = .22, p = .050, R² = .05). Borderline features were unrelated to pain threshold and TSSP decay. A stepwise regression showed greater TSSP in individuals with greater borderline features was accounted for by the negative relationships factor rather than the affect dysregulation factor. The results of mediational analyses showed depression and blunted sympathetic skin conductance responses mediated the positive association between TSSP and borderline features.

Altered somatosensory profile according to quantitative sensory testing in patients with degenerative lumbar spine disorders scheduled for surgery

Background

Somatosensory profiling in affected and non-affected body regions can strengthen our insight regarding the underlying pain mechanisms, which can be valuable in treatment decision making and to improve outcomes, in patients with degenerative lumbar spine disorders pre-surgery. The aim was to describe somatosensory profiles in patients with degenerative lumbar spine disorders, to identify the proportion with altered somatosensory profile, and to analyze demographic characteristics, self-reported function, pain, and health pre- and 3 months post-surgery.

Methods

In this prospective cohort study in a Spine Clinic, 105 patients scheduled for surgery for spinal stenosis, disc herniation, degenerative disc disease, or spondylolisthesis were consecutively recruited. Exclusion criteria were; indication for acute surgery or previous surgery at the same spinal level or severe grade of pathology. Quantitative sensory testing (QST) and self-reported function, pain, and health was measured pre- and 3 months post-surgery. The somatosensory profile included cold detection threshold, warmth detection threshold, cold pain threshold, heat pain threshold and pressure pain threshold in affected and non-affected body regions.

Results

On a group level, the patients’ somatosensory profiles were within the 95% confidence interval (CI) from normative reference data means. On an individual level, an altered somatosensory profile was defined as having two or more body regions (including a non-affected region) with QST values outside of normal ranges for reference data. The 23 patients (22%) with altered somatosensory profiles, with mostly loss of function, were older (P = 0.031), more often female (P = 0.005), had higher back and leg pain (P = 0.016, 0.020), lower mental health component summary score (SF-36 MCS) (P = 0.004) and larger pain distribution (P = 0.047), compared to others in the cohort. Post-surgery there was a tendency to worse pain, function and health in the group with altered somatosensory profile pre-surgery.

Conclusions

On a group level, patients with degenerative lumbar spine disorders scheduled for surgery were within normal range for the QST measurements compared to reference values. On an individual level, an altered somatosensory profile outside of normal range in both affected and non-affected body regions occurred in 22% of patients, which may indicate disturbed somatosensory function. Those patients had mostly loss of sensory function and had worse self-reported outcome pre-surgery, compared to the rest of the cohort. Future prospective studies are needed to further examine whether these dimensions can be useful in predicting post-surgery outcome and guide need of additional treatments.

Evidence and consensus recommendations for the pharmacological management of pain in India

Despite enormous progress in the field of pain management over the recent years, pain continues to be a highly prevalent medical condition worldwide. In the developing countries, pain is often an undertreated and neglected aspect of treatment. Awareness issues and several misconceptions associated with the use of analgesics, fear of adverse events - particularly with opioids and surgical methods of analgesia - are major factors contributing to suboptimal treatment of pain. Untreated pain, as a consequence, is associated with disability, loss of income, unemployment and considerable mortality; besides contributing majorly to the economic burden on the society and the health care system in general. Available guidelines suggest that a strategic treatment approach may be helpful for physicians in managing pain in real-world settings. The aim of this manuscript is to propose treatment recommendations for the management of different types of pain, based on the available evidence. Evidence search was performed by using MEDLINE (by PubMed) and Cochrane databases. The types of articles included in this review were based on randomized control studies, case-control or cohort studies, prospective and retrospective studies, systematic reviews, meta-analyses, clinical practice guidelines and evidence-based consensus recommendations. Articles were reviewed by a multidisciplinary expert panel and recommendations were developed. A stepwise treatment algorithm-based approach based on a careful diagnosis and evaluation of the underlying disease, associated comorbidities and type/duration of pain is proposed to assist general practitioners, physicians and pain specialists in clinical decision making.

Thermal quantitative sensory testing in healthy Dutch children and adolescents standardized test paradigm and Dutch reference values

Background

Quantitative sensory testing (QST) is often used to measure children’s and adults’ detection- and pain thresholds in a quantitative manner. In children especially the Thermal Sensory Analyzer (TSA-II) is often applied to determine thermal detection and pain thresholds. As comparisons between studies are hampered by the different testing protocols used, we aimed to present a standard protocol and reference values for thermal detection- and pain thresholds in children.

Methods

Our standard testing protocol includes reaction time dependent and independent tests and takes about 14–18 min to complete. Reference values were obtained from a sample of 69 healthy term born children and adolescents with a median age of 11.2 years (range 8.2 to 17.9 years old). Seventy-one children were recruited and data of 28 males and 41 females was obtained correctly. We studied possible age and sex differences.

Results

This study provides Dutch reference values and presents a standard quantitative sensory testing protocol for children with an age from 8 years onwards. This protocol appeared to be feasible, since only two out of 71 participants were not able to correctly complete the protocol due to attention deficits and were therefore excluded. We found some significant age and sex differences: females were statistically significantly more sensitive for both cold and heat pain compared to males, and the youngest children (8–9 years old) were less sensitive to detect a warm stimulus. The youngest children tend to be more sensitive to heat pain in comparison to older participants, although the difference was not statistically significant.

Conclusions

We present a feasible thermal quantitative sensory testing protocol for children and reference values that are easy to interpret and may serve as normative values for future studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-017-0827-7) contains supplementary material, which is available to authorized users.

Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations

There is tremendous interpatient variability in the response to analgesic therapy (even for efficacious treatments), which can be the source of great frustration in clinical practice. This has led to calls for "precision medicine" or personalized pain therapeutics (ie, empirically based algorithms that determine the optimal treatments, or treatment combinations, for individual patients) that would presumably improve both the clinical care of patients with pain and the success rates for putative analgesic drugs in phase 2 and 3 clinical trials. However, before implementing this approach, the characteristics of individual patients or subgroups of patients that increase or decrease the response to a specific treatment need to be identified. The challenge is to identify the measurable phenotypic characteristics of patients that are most predictive of individual variation in analgesic treatment outcomes, and the measurement tools that are best suited to evaluate these characteristics. In this article, we present evidence on the most promising of these phenotypic characteristics for use in future research, including psychosocial factors, symptom characteristics, sleep patterns, responses to noxious stimulation, endogenous pain-modulatory processes, and response to pharmacologic challenge. We provide evidence-based recommendations for core phenotyping domains and recommend measures of each domain.

The power function of the ten test for measuring neural sensitivity in clinical pain or sensory abnormalities

This review highlights a simple psychophysical quantitative sensory testing (QST) method (the ten test) for research and clinical practice as it relates to sensitivity change and symptom improvement in pain populations. This cost-effective QST has a three-fold benefit of being diagnostic, prognostic and providing outcome evaluation. The power function of the ten test is discussed with the theoretical foundation of levels of measurement and psychophysical method that can approach ratio scaling in mind. The ratio level measurement might be useful for the researcher as the normative values of different QSTs are not well established. As a reliable and valid testing method, it provides an option for clinicians in busy clinical settings, and/or where QST equipment is unavailable.

Effects of a Pain Catastrophizing Induction on Sensory Testing in Women with Chronic Low Back Pain: A Pilot Study

Pain catastrophizing, a pattern of negative cognitive-emotional responses to actual or anticipated pain, maintains chronic pain and undermines response to treatments. Currently, precisely how pain catastrophizing influences pain processing is not well understood. In experimental settings, pain catastrophizing has been associated with amplified pain processing. This study sought to clarify pain processing mechanisms via experimental induction of pain catastrophizing. Forty women with chronic low back pain were assigned in blocks to an experimental condition, either a psychologist-led 10-minute pain catastrophizing induction or a control (10-minute rest period). All participants underwent a baseline round of several quantitative sensory testing (QST) tasks, followed by the pain catastrophizing induction or the rest period, and then a second round of the same QST tasks. The catastrophizing induction appeared to increase state pain catastrophizing levels. Changes in QST pain were detected for two of the QST tasks administered, weighted pin pain and mechanical allodynia. Although there is a need to replicate our preliminary results with a larger sample, study findings suggest a potential relationship between induced pain catastrophizing and central sensitization of pain. Clarification of the mechanisms through which catastrophizing affects pain modulatory systems may yield useful clinical insights into the treatment of chronic pain.

Dynamic Quantitative Sensory Testing to Characterize Central Pain Processing

Central facilitation and modulation of incoming nociceptive signals play an important role in the perception of pain. Disruption in central pain processing is present in many chronic pain conditions and can influence responses to specific therapies. Thus, the ability to precisely describe the state of central pain processing has profound clinical significance in both prognosis and prediction. Because it is not practical to record neuronal firings directly in the human spinal cord, surrogate behavior tests become an important tool to assess the state of central pain processing. Dynamic QST is one such test, and can probe both the ascending facilitation and descending modulation of incoming nociceptive signals via TS and CPM, respectively. Due to the large between-individual variability in the sensitivity to noxious signals, standardized TS and CPM tests may not yield any meaningful data in up to 50% of the population due to floor or ceiling effects. We present methodologies to individualize TS and CPM so we can capture these measures in a broader range of individuals than previously possible. We have used these methods successfully in several studies at the lab, and data from one ongoing study will be presented to demonstrate feasibility and potential applications of the methods.

Predictors of opioid efficacy in patients with chronic pain: A prospective multicenter observational cohort study

Opioids are increasingly used for treatment of chronic pain. However, they are only effective in a subset of patients and have multiple side effects. Thus, studies using biomarkers for response are highly warranted. The current study prospectively examined 63 opioid-naïve patients initiating opioid use for diverse types of chronic pain at five European centers. Quantitative sensory testing, electroencephalography (EEG) recordings, and assessment of pain catastrophizing were performed prior to treatment. The co-primary outcomes were change from baseline in ratings of chronic pain and quality of life after 14 days of opioid treatment. Secondary outcomes included patient’s global impression of clinical change and side effects. Logistic regression models adjusted for age and sex were used to identify biomarkers predictive for successful treatment, defined as at least a 30% reduction in average pain intensity or an improvement in quality of life of at least 10 scale points. Fifty-nine patients (94%) completed the study. The mean age was 55 ± 16 years and 69% were females. Pain reduction was predicted by cold pain intensity (OR: 0.69; P = 0.01), pain catastrophizing (OR: 0.82; P = 0.03), relative delta (OR: 0.76; P = 0.03) and beta EEG activity (OR: 1.18; P = 0.04) induced by experimental cold pain. None of the study variables were related to improvement in quality of life. For the first time, individual pain processing characteristics have been linked to opioid response in a mixed chronic pain population. This has the potential to personalize treatment of chronic pain and restrict opioid use to patients with high likelihood for response.

Characteristics of the local cutaneous sensory thermoneutral zone

Skin temperature detection thresholds have been used to measure human cold and warm sensitivity across the temperature continuum. They exhibit a sensory zone within which neither warm nor cold sensations prevail. This zone has been widely assumed to coincide with steady-state local skin temperatures between 32 and 34°C, but its underlying neurophysiology has been rarely investigated. In this study we employ two approaches to characterize the properties of sensory thermoneutrality, testing for each whether neutrality shifts along the temperature continuum depending on adaptation to a preceding thermal state. The focus is on local spots of skin on the palm. Ten participants (age: 30.3 ± 4.8 yr) underwent two experiments. Experiment 1 established the cold-to-warm inter-detection threshold range for the palm's glabrous skin and its shift as a function of 3 starting skin temperatures (26, 31, or 36°C). For the same conditions, experiment 2 determined a thermally neutral zone centered around a thermally neutral point in which thermoreceptors' activity is balanced. The zone was found to be narrow (~0.98 to ~1.33°C), moving with the starting skin temperature over the temperature span 27.5-34.9°C (Pearson r = 0.94; P < 0.001). It falls within the cold-to-warm inter-threshold range (~2.25 to ~2.47°C) but is only half as wide. These findings provide the first quantitative analysis of the local sensory thermoneutral zone in humans, indicating that it does not occur only within a specific range of steady-state skin temperatures (i.e., it shifts across the temperature continuum) and that it differs from the inter-detection threshold range both quantitatively and qualitatively. These findings provide insight into thermoreception neurophysiology.NEW & NOTEWORTHY Contrary to a widespread concept in human thermoreception, we show that local sensory thermoneutrality is achievable outside the 32-34°C skin temperature range. We propose that sensory adaption underlies a new mechanism of temperature integration. Also, we have developed from vision research a new quantitative test addressing the balance in activity of cutaneous cold and warm thermoreceptors. This could have important clinical (assessment of somatosensory abnormalities in neurological disease) and applied (design of personal comfort systems) implications.

T4 Syndrome: A Scoping Review of the Literature

OBJECTIVE

The purpose of this scoping review was to identify any available evidence regarding T4 syndrome.

METHODS

Databases were searched from inception through October 2015 and included PubMed, CINAHL, PEDro, Google Scholar, Osteomed-DR; Index to Chiropractic Literature, PROSPERO, and Chiroaccess. All studies with information about T4 syndrome that were published in a peer-reviewed journal or textbook were included. The information was organized in the format of the International Classification of Functioning, Disability, and Health. Studies were ranked using Sackett's levels of evidence.

RESULTS

Eight articles met the inclusion criteria. Studied areas included theoretical pathophysiology and symptom etiology, diagnosis, symptoms, treatment, and outcomes of T4 syndrome. The methodological quality of included studies was low.

CONCLUSION

T4 syndrome is a diagnosis of exclusion that appears to be rare. It has been treated conservatively in the literature using mobilization and exercise. There is no high-quality evidence published about T4 syndrome, and we caution clinicians when considering it as a primary means to determine patient care.

Heat pain detection threshold is associated with the area of secondary hyperalgesia following brief thermal sensitization: a study of healthy male volunteers

Introduction

The area of secondary hyperalgesia following brief thermal sensitization (BTS) of the skin and heat pain detection thresholds (HPDT) may both have predictive abilities in regards to pain sensitivity and clinical pain states. The association between HPDT and secondary hyperalgesia, however, remains unsettled, and the dissimilarities in physiologic properties suggest that they may represent 2 distinctively different pain entities. The aim of this study was to investigate the association between HPDT and BTS-induced secondary hyperalgesia.

Methods

A sample of 121 healthy male participants was included and tested on 2 separate study days with BTS (45°C, 3 minutes), HPDT, and pain during thermal stimulation (45°C, 1 minute). Areas of secondary hyperalgesia were quantified after monofilament pinprick stimulation. The pain catastrophizing scale (PCS) and hospital anxiety and depression scale (HADS) were also applied.

Results

A significant association between HPDT and the size of the area of secondary hyperalgesia (p<0.0001) was found. The expected change in area of secondary hyperalgesia due to a 1-degree increase in HPDT was estimated to be −27.38 cm², 95% confidence interval (CI) of −37.77 to −16.98 cm², with an R² of 0.19. Likewise, a significant association between HADS-depression subscore and area of secondary hyperalgesia (p=0.046) was found, with an estimated expected change in secondary hyperalgesia to a 1-point increase in HADS-depression subscore of 11 cm², 95% CI (0.19–21.82), and with R² of 0.03. We found no significant associations between secondary hyperalgesia area and PCS score or pain during thermal stimulation.

Conclusion

HPDT and the area of secondary hyperalgesia after BTS are significantly associated; however, with an R² of only 19%, HPDT only offers a modest explanation of the inter-participant variation in the size of the secondary hyperalgesia area elicited by BTS.

Quantitative sensory testing and pain-evoked cytokine reactivity: comparison of patients with sickle cell disease to healthy matched controls

Sickle cell disease (SCD) is an inherited blood disorder associated with significant morbidity, which includes severe episodic pain, and, often, chronic pain. Compared to healthy individuals, patients with SCD report enhanced sensitivity to thermal detection and pain thresholds and have altered inflammatory profiles, yet no studies to date have examined biomarker reactivity after laboratory-induced pain. We sought to examine this relationship in patients with SCD compared to healthy control participants. We completed quantitative sensory testing in 83 patients with SCD and sequential blood sampling in 27 of them, whom we matched (sex, age, race, body mass index, and education) to 27 healthy controls. Surprisingly, few quantitative sensory testing differences emerged between groups. Heat pain tolerance, pressure pain threshold at the trapezius, thumb, and quadriceps, and thermal temporal summation at 45°C differed between groups in the expected direction, whereas conditioned pain modulation and pain ratings to hot water hand immersion were counterintuitive, possibly because of tailoring the water temperature to a perceptual level; patients with SCD received milder temperatures. In the matched subsample, group differences and group-by-time interactions were observed in biomarkers including tumor necrosis factor alpha, interleukin-1ß, interleukin-4, and neuropeptide Y. These findings highlight the utility of laboratory pain testing methods for understanding individual differences in inflammatory cytokines. Our findings suggest amplified pain-evoked proinflammatory cytokine reactivity among patients with SCD relative to carefully matched controls. Future research is warranted to evaluate the impact of enhanced pain-related cytokine response and whether it is predictive of clinical characteristics and the frequency/severity of pain crises in patients with SCD.

Lack of genetic association between OCT1, ABCB1, and UGT2B7 variants and morphine pharmacokinetics

AIM

A high inter-individual variation in the pharmacokinetics and pharmacodynamics of morphine has been observed. Genetic polymorphisms in genes encoding the organic cation transporter isoform 1 (OCT1), the efflux transporter p-glycoprotein (ABCB1), and the UDP-glucuronosyltransferase-2B7 (UGT2B7) may influence morphine pharmacokinetics and thus, also pharmacodynamics. The aim of this study was to evaluate the association between OCT1, ABCB1, and UGT2B7 variants, and morphine pharmacokinetics and -dynamics in healthy volunteers.

METHODS

Pharmacokinetic and pharmacodynamic data were collected from a double-blinded, randomized, crossover trial in 37 healthy subjects. Pharmacokinetic data were analyzed in NONMEM®, and the time-concentration relationship of morphine, morphine-3-glucuronide, and morphine-6-glucuronide was parameterized as the transit compartment rate constant (k_tr), clearance (CL), and volume of distribution (V_D). The area under the plasma concentration-time curve (AUC_0-150min) and the maximum plasma concentration (C_max) were also calculated. Pharmacodynamic data were measured as pain tolerance thresholds to mechanical stimulation of the rectum and muscle, as well as tonic cold pain stimulation ("the cold pressor test" where hand was immersed in cold water). Six different single nucleotide polymorphisms in three different genes (OCT1 (n=22), ABCB1 (n=37), and UGT2B (n=22)) were examined.

RESULTS

Neither AUC_0-150min, k_tr, CL, nor V_D were associated with genetic variants in OCT1, ABCB1, and UGT2B7 (all P>0.05). Similarly, the antinociceptive effects of morphine on rectal, muscle, and cold pressor tests were not associated with these genetic variants (all P>0.05).

CONCLUSIONS

In this experimental study in healthy volunteers, we found no association between different genotypes of OCT1, ABCB1, and UGT2B7, and morphine pharmacokinetics and pharmacodynamics. Nonetheless, due to methodological limitations we cannot exclude that associations exist.

Frida Kahlo: Portrait of Chronic Pain

The Mexican artist Frida Kahlo (1907-1954) is one of the most celebrated artists of the 20th century. Although famous for her colorful self-portraits and associations with celebrities Diego Rivera and Leon Trotsky, less known is the fact that she had lifelong chronic pain. Frida Kahlo developed poliomyelitis at age 6 years, was in a horrific trolley car accident in her teens, and would eventually endure numerous failed spinal surgeries and, ultimately, limb amputation. She endured several physical, emotional, and psychological traumas in her lifetime, yet through her art, she was able to transcend a life of pain and disability. Of her work, her self-portraits are conspicuous in their capacity to convey her life experience, much of which was imbued with chronic pain. Signs and symptoms of chronic neuropathic pain and central sensitization of nociceptive pathways are evident when analyzing her paintings and medical history. This article uses a narrative approach to describe how events in the life of this artist contributed to her chronic pain. The purpose of this article is to discuss Frida Kahlo's medical history and her art from a modern pain sciences perspective, and perhaps to increase our understanding of the pain experience from the patient's perspective.

The Cold Pressor Test as a Predictor of Prolonged Postoperative Pain, a Prospective Cohort Study

INTRODUCTION

Presently, it is difficult to predict which patients are at increased risk of ongoing pain problems postoperatively. This study followed a group of patients from the week before their operation until 3 months after it, to identify potential risk variables.

METHODS

Fifty-four patients undergoing moderate-major gynaecological surgery at Christchurch Women's Hospital were recruited and assessed preoperatively over an 11-week period. At this initial assessment, participants were subjected to a cold pressor test (CPT). Telephonic follow-up was conducted at 6 weeks and 3 months postoperatively, to determine pain status. Information regarding the type of operation and surgical approach was collected from hospital records.

RESULTS

Pain threshold (time taken to report the onset of pain), as measured by the CPT, was significantly predictive of prolonged pain outcomes (area under the curve = 0.80, 95 % CI 0.66, 0.95). Pain tolerance (total time taken to end the CPT voluntarily) was similarly predictive but non-significant (area under the curve = 0.69, 95 % CI 0.47, 0.90).

CONCLUSION

The preoperative cold pressor test shows some promise for predicting ongoing postoperative pain. However, more research is needed to determine the clinical significance of these findings in larger samples and how they could be incorporated into clinical practice.

Psychophysical and Patient Factors as Determinants of Pain, Function and Health Status in Shoulder Disorders

Objective:

To estimate the extent to which psychophysical quantitative sensory test (QST) and patient factors (gender, age and comorbidity) predict pain, function and health status in people with shoulder disorders. To determine if there are gender differences for QST measures in current perception threshold (CPT), vibration threshold (VT) and pressure pain (PP) threshold and tolerance.

Design:

A cross-sectional study design.

Setting:

MacHAND Clinical Research Lab at McMaster University.

Subjects:

34 surgical and 10 nonsurgical participants with shoulder pain were recruited.

Method:

Participants completed the following patient reported outcomes: pain (Numeric Pain Rating, Pain Catastrophizing Scale, Shoulder Pain and Disability Index) and health status (Short Form-12). Participants completed QST at 4 standardized locations and then an upper extremity performance-based endurance test (FIT-HaNSA). Pearson r’s were computed to determine the relationships between QST variables and patient factors with either pain, function or health status. Eight regression models were built to analysis QST’s and patient factors separately as predictors of either pain, function or health status. An independent sample t-test was done to evaluate the gender effect on QST.

Results:

Greater PP threshold and PP tolerance was significantly correlated with higher shoulder functional performance on the FIT-HANSA (r =0.31-0.44) and lower self-reported shoulder disability (r = -0.32 to -0.36). Higher comorbidity was consistently correlated (r =0.31-0.46) with more pain, and less function and health status. Older age was correlated to more pain intensity and less function (r =0.31-0.57). In multivariate models, patient factors contributed significantly to pain, function or health status models (r² =0.19-0.36); whereas QST did not. QST was significantly different between males and females [in PP threshold (3.9 vs. 6.2, p < .001) and PP tolerance (7.6 vs. 2.6, p < .001) and CPT (1.6 vs. 2.3, p =.02)].

Conclusion:

Psychophysical dimensions and patient factors (gender, age and comorbidity) affect self-reported and performance-based outcome measures in people with shoulder disorders.

Prognostic value of quantitative sensory testing in low back pain: a systematic review of the literature

Quantitative sensory testing (QST) measures have recently been shown to predict outcomes in various musculoskeletal and pain conditions. The aim of this systematic review was to summarize the emerging body of evidence investigating the prognostic value of QST measures in people with low back pain (LBP). The protocol for this review was prospectively registered on the International Prospective Register of Systematic Reviews. An electronic search of six databases was conducted from inception to October 2015. Experts in the field were contacted to retrieve additional unpublished data. Studies were included if they were prospective longitudinal in design, assessed at least one QST measure in people with LBP, assessed LBP status at follow-up, and reported the association of QST data with LBP status at follow-up. Statistical pooling of results was not possible due to heterogeneity between studies. Of 6,408 references screened after duplicates removed, three studies were finally included. None of them reported a significant association between the QST measures assessed and the LBP outcome. Three areas at high risk of bias were identified which potentially compromise the validity of these results. Due to the paucity of available studies and the methodological shortcomings identified, it remains unknown whether QST measures are predictive of outcome in LBP.

Intra-session absolute and relative reliability of pressure pain thresholds in the low back region of vine-workers: ffect of the number of trials

BACKGROUND

Pressure pain thresholds (PPT) are commonly used to quantify mechanical pain sensitivity of deep structures. Excellent PPT reliability has been previously reported among the low back of healthy subjects. However, there is a lack of studies assessing PPT over the low back of workers exposed to biomechanical risk factors of low back pain. Thus, the purpose of this study was threefold: (1) to evaluate the intra-session absolute and relative reliability as well as minimal detectable change (MDC) values of PPT within 14 locations covering the low back region of vine-workers and (2) to determine the number of trial required to ensure reliable PPT assessments and (3) to assess the effect of modifier factors such as gender, age, body mass index (BMI) and pain intensity on PPT reliability.

METHODS

Twenty-nine vine-workers voluntarily participated in this study. Twenty-two reported low intensity of low-back pain while seven were pain-free. PPTs were assessed among 14 anatomical locations in the lower back region. Three trials were performed on each location with an interval time of at least one minute. Reliability was assessed computing intraclass correlation coefficients (ICC), standard error of measurement (SEM) for all possible combinations between trials. Bland-Altman plots were also generated to assess potential bias in the dataset. Finally, a repeated measure analysis of variance (RM-ANOVA) with the number of trials used as within subject factor was performed on (1) PPT, (2) ICC and (3) SEM values.

RESULTS

ICC ranged from 0.86 to 0.99 for all anatomical locations and for all possible combinations between trials. SEM for comparison between trial 1-2, 2-3, 1-3 and, 1-2-3 ranged from respectively, 36.7-77.5, 27.8-77.7, 50-95.2 and, 39.3-80.8 kPa. ICC and SEM remained similar to the ones obtained for the entire population when taking modifier factors in consideration. The visual analysis of Bland-Altman plots suggested small measurement errors for all anatomical locations and for all possible combinations between trials.

CONCLUSIONS

The assessment of PPTs of the lower back among vine-workers was found to have excellent relative and absolute reliability. Moreover, reliable measurements can be equally achieved when using the mean of three PPT measurement or with the first one.

Heightened Temporal Summation of Pain in Patients with Functional Gastrointestinal Disorders and History of Trauma

BACKGROUND

Individuals with functional gastrointestinal disorders (FGIDs) report experiencing trauma more often than healthy controls, but little is known regarding psychophysical correlates.

PURPOSE

The purpose of this study was to test the hypothesis that adolescents and young adults with FGIDs since childhood and a trauma history (n = 38) would exhibit heightened temporal summation to thermal pain stimuli, an index of central sensitization, and greater clinical symptoms compared to patients with FGIDs and no trauma history (n = 95) and healthy controls (n = 135).

METHODS

Participants completed self-report measures, an experimental pain protocol, and psychiatric diagnostic interview as part of a larger longitudinal study.

RESULTS

FGID + Trauma patients exhibited greater temporal summation than FGID + No Trauma patients and healthy controls. Additionally, FGID + Trauma patients exhibited greater gastrointestinal and non-gastrointestinal symptom severity, number of chronic pain sites, and disability.

CONCLUSIONS

Assessing for trauma history in patients with FGIDs could identify a subset at risk for greater central sensitization and pain-related symptoms.

Is One Trial Sufficient to Obtain Excellent Pressure Pain Threshold Reliability in the Low Back of Asymptomatic Individuals? A Test-Retest Study

The assessment of pressure pain threshold (PPT) provides a quantitative value related to the mechanical sensitivity to pain of deep structures. Although excellent reliability of PPT has been reported in numerous anatomical locations, its absolute and relative reliability in the lower back region remains to be determined. Because of the high prevalence of low back pain in the general population and because low back pain is one of the leading causes of disability in industrialized countries, assessing pressure pain thresholds over the low back is particularly of interest. The purpose of this study study was (1) to evaluate the intra- and inter- absolute and relative reliability of PPT within 14 locations covering the low back region of asymptomatic individuals and (2) to determine the number of trial required to ensure reliable PPT measurements. Fifteen asymptomatic subjects were included in this study. PPTs were assessed among 14 anatomical locations in the low back region over two sessions separated by one hour interval. For the two sessions, three PPT assessments were performed on each location. Reliability was assessed computing intraclass correlation coefficients (ICC), standard error of measurement (SEM) and minimum detectable change (MDC) for all possible combinations between trials and sessions. Bland-Altman plots were also generated to assess potential bias in the dataset. Relative reliability for both intra- and inter- session was almost perfect with ICC ranged from 0.85 to 0.99. With respect to the intra-session, no statistical difference was reported for ICCs and SEM regardless of the conducted comparisons between trials. Conversely, for inter-session, ICCs and SEM values were significantly larger when two consecutive PPT measurements were used for data analysis. No significant difference was observed for the comparison between two consecutive measurements and three measurements. Excellent relative and absolute reliabilities were reported for both intra- and inter-session. Reliable measurements can be equally achieved when using the mean of two or three consecutive PPT measurements, as usually proposed in the literature, or with only the first one. Although reliability was almost perfect regardless of the conducted comparison between PPT assessments, our results suggest using two consecutive measurements to obtain higher short term absolute reliability.

Does central sensitization help explain idiopathic overactive bladder?

The pathophysiological mechanisms underlying overactive bladder syndrome (OAB) can include dysfunction of sensory pathways of the peripheral and central nervous systems, resulting in bladder hypersensitivity. Central sensitization describes an induced state of spinal hypersensitivity that is associated with a variety of chronic pain disorders that share many attributes with OAB, albeit without the presence of pain. As such, the concept of central sensitization might be relevant to understanding the mechanisms and clinical manifestations of OAB syndrome. An understanding of the pathophysiology and clinical manifestations of central sensitization, and the evidence that supports a role of central sensitization in OAB, including the potential implications of mechanisms of central sensitization for the treatment of patients with OAB could provide a novel approach to the treatment of patients with this disease. Such an approach would be especially relevant to those patients with central sensitization-related comorbidities, and has the potential to improve the outcomes of these patients in particular.

Variability in conditioned pain modulation predicts response to NSAID treatment in patients with knee osteoarthritis

Background

Patients with painful knee osteoarthritis (OA) demonstrate hyperalgesia and altered pain-modulatory responses. While some prior work has demonstrated cross-sectional associations between laboratory and clinical pain measures, it is unknown whether individual variability in quantitative sensory testing (QST) responses at baseline can prospectively predict analgesic treatment responses.

Method

Patients with knee OA (n = 35) were compared on QST responses to a demographically-matched pain-free control group (n = 39), after which patients completed a month-long treatment study of diclofenac sodium topical gel (1 %), applied up to 4 times daily.

Results

OA patients demonstrated reduced pain thresholds at multiple anatomic sites, as well as reduced conditioned pain modulation (CPM) and enhanced temporal summation of pain. The most pain-sensitive patients tended to report the most intense and neuropathic OA pain. Following diclofenac treatment, the knee OA cohort showed a roughly 30 % improvement in pain, regardless of the presence or absence of neuropathic symptoms. Baseline CPM scores, an index of endogenous pain-inhibitory capacity, were prospectively associated with treatment-related changes in clinical pain. Specifically, participants with higher CPM at baseline (i.e., better functioning endogenous pain-inhibitory systems) showed more reduction in pain at the end of treatment (p < .05).

Conclusions

These results support prior findings of amplified pain sensitivity and reduced pain-inhibition in OA patients. Moreover, the moderate to strong associations between laboratory-based measures of pain sensitivity and indices of clinical pain highlight the clinical relevance of QST in this sample. Finally, the prospective association between CPM and diclofenac response suggests that QST-based phenotyping may have utility in explaining inter-patient variability in long-term analgesic treatment outcomes.

Trial registration

ClinicalTrials.Gov Identifier: NCT01383954. Registered June 22, 2011.

Is heat pain detection threshold associated with the area of secondary hyperalgesia following brief thermal sensitization? A study of healthy volunteers - design and detailed plan of analysis

Background

Several factors are believed to influence the development and experience of pain.

Human clinical pain models are central tools, in the investigation of basic physiologic pain responses, and can be applied in patients as well as in healthy volunteers. Each clinical pain model investigates different aspects of the human pain response.

Brief thermal sensitization induces a mild burn injury, resulting in development of primary hyperalgesia at the site of stimulation, and secondary hyperalgesia surrounding the site of stimulation. Central sensitization is believed to play an important role in the development of secondary hyperalgesia; however, a possible association of secondary hyperalgesia following brief thermal sensitization and other heat pain models remains unknown. Our aim with this study is to investigate how close the heat pain detection threshold is associated with the size of the area of secondary hyperalgesia induced by the clinical heat pain model: Brief thermal sensitization.

Methods and design

We aim to include 120 healthy participants. The participants will be tested on two separate study days with the following procedures: i) Brief thermal sensitization, ii) heat pain detection threshold and iii) pain during thermal stimulation. Additionally, the participants will be tested with the Pain Catastrophizing Scale and Hospital Anxiety and Depression Scale questionnaires.

We conducted statistical simulations based on data from our previous study, to estimate an empirical power of 99.9 % with α of 0.05. We define that an R² < 0.25 and predictive intervals larger than +/−150 cm² are indications of a weak association.

Discussion

The area of secondary hyperalgesia may serve as a quantitative measure of the central sensitization induced by cutaneous heat stimulation, and thus may be a biomarker of an individual’s pain sensitivity. The number of studies investigating secondary hyperalgesia is growing; however basic knowledge of the physiologic aspects of secondary hyperalgesia in humans is still incomplete. We therefore find it interesting to investigate if HPDT, a known quantitative sensory test, is associated with areas of secondary hyperalgesia following brief thermal sensitization

Trial registration

Clinicaltrials.gov (Identifier: NCT02527395). Danish Research Ethics Committee (Identifier: H-8-2014-012). Danish Data Protection Agency (Identifier: 30-1436).

Electronic supplementary material

The online version of this article (doi:10.1186/s12871-016-0193-2) contains supplementary material, which is available to authorized users.

Responsiveness of electrical nociceptive detection thresholds to capsaicin (8 %)-induced changes in nociceptive processing

Pain disorders can be initiated and maintained by malfunctioning of one or several mechanisms underlying the nociceptive function. Psychophysical procedures allow the estimation of nociceptive detection thresholds using intra-epidermal electrical stimuli. By varying the temporal properties of electrical stimuli, various contributions of nociceptive processes to stimulus processing can be observed. To observe the responsiveness of nociceptive thresholds to changes in nociceptive function, a model of capsaicin-induced nerve defunctionalization was used. Its effect on nociceptive detections thresholds was investigated over a period of 84 days. A cutaneous capsaicin (8 %) patch was applied for 60 min to the upper leg of eight healthy human participants. Single- and double-pulse electrical stimuli were presented in a pseudo-random order using an intra-epidermal electrode. Stimuli and corresponding responses were recorded on both treated and untreated skin areas prior to capsaicin application and on days 2, 7, 28, and 84. Increases in electrical detection thresholds at the capsaicin area were observed on days 2 and 7 for single-pulse stimuli. Detection thresholds corresponding to double-pulse stimuli were increased on days 7 and 28, suggesting a delayed and longer lasting effect on double-pulse stimuli. In the present study, it was demonstrated that the responsiveness of detection thresholds to capsaicin application depends on the temporal properties of electrical stimuli. The observation of capsaicin-induced changes by estimation of detection thresholds revealed different time patterns of contributions of peripheral and central mechanisms to stimulus processing.

Association between Gene Polymorphisms and Pain Sensitivity Assessed in a Multi-Modal Multi-Tissue Human Experimental Model - An Explorative Study

The genetic influence on sensitivity to noxious stimuli (pain sensitivity) remains controversial and needs further investigation. In the present study, the possible influence of polymorphisms in three opioid receptor (OPRM, OPRD and OPRK) genes and the catechol-O-methyltransferase (COMT) gene on pain sensitivity in healthy participants was investigated. Catechol-O-methyltransferase has an indirect effect on the mu opioid receptor by changing its activity through an altered endogenous ligand effect. Blood samples for genetic analysis were withdrawn in a multi-modal and multi-tissue experimental pain model in 40 healthy participants aged 20-65. Seventeen different single nucleotide polymorphisms in different genes (OPRM, OPRK, OPRD and COMT) were included in the analysis. Experimental pain tests included thermal skin stimulation, mechanical muscle and bone stimulation and mechanical, electrical and thermal visceral stimulations. A cold pressor test was also conducted. DNA was available from 38 of 40 participants. Compared to non-carriers of the COMT rs4680A allele, carriers reported higher bone pressure pain tolerance threshold (i.e. less pain) by up to 23.8% (p < 0.015). Additionally, carriers of the C allele (CC/CT) of OPRK rs6473799 reported a 30.4% higher mechanical visceral pain tolerance threshold than non-carriers (TT; p < 0.019). For the other polymorphisms and stimulations, no associations were found (all p > 0.05). In conclusion, COMT rs4680 and OPRK rs6473799 polymorphisms seem to be associated with pain sensitivity. Thus, the findings support a possible genetic influence on pain sensitivity.

Effect of low-frequency deep brain stimulation on sensory thresholds in Parkinson's disease

OBJECTIVE Chronic pain is a major distressing symptom of Parkinson's disease (PD) that is often undertreated. Subthalamic nucleus (STN) deep brain stimulation (DBS) delivers high-frequency stimulation (HFS) to patients with PD and has been effective in pain relief in a subset of these patients. However, up to 74% of patients develop new pain concerns while receiving STN DBS. Here the authors explore whether altering the frequency of STN DBS changes pain perception as measured through quantitative sensory testing (QST). METHODS Using QST, the authors measured thermal and mechanical detection and pain thresholds in 19 patients undergoing DBS via HFS, low-frequency stimulation (LFS), and off conditions in a randomized order. Testing was performed in the region of the body with the most pain and in the lower back in patients without chronic pain. RESULTS In the patients with chronic pain, LFS significantly reduced heat detection thresholds as compared with thresholds following HFS (p = 0.029) and in the off state (p = 0.010). Moreover, LFS resulted in increased detection thresholds for mechanical pressure (p = 0.020) and vibration (p = 0.040) compared with these thresholds following HFS. Neither LFS nor HFS led to changes in other mechanical thresholds. In patients without chronic pain, LFS significantly increased mechanical pain thresholds in response to the 40-g pinprick compared with thresholds following HFS (p = 0.032). CONCLUSIONS Recent literature has suggested that STN LFS can be useful in treating nonmotor symptoms of PD. Here the authors demonstrated that LFS modulates thermal and mechanical detection to a greater extent than HFS. Low-frequency stimulation is an innovative means of modulating chronic pain in PD patients receiving STN DBS. The authors suggest that STN LFS may be a future option to consider when treating Parkinson's patients in whom pain remains the predominant complaint.

Determining Pain Detection and Tolerance Thresholds Using an Integrated, Multi-Modal Pain Task Battery

Human pain models are useful in the assessing the analgesic effect of drugs, providing information about a drug's pharmacology and identify potentially suitable therapeutic populations. The need to use a comprehensive battery of pain models is highlighted by studies whereby only a single pain model, thought to relate to the clinical situation, demonstrates lack of efficacy. No single experimental model can mimic the complex nature of clinical pain. The integrated, multi-modal pain task battery presented here encompasses the electrical stimulation task, pressure stimulation task, cold pressor task, the UVB inflammatory model which includes a thermal task and a paradigm for inhibitory conditioned pain modulation. These human pain models have been tested for predicative validity and reliability both in their own right and in combination, and can be used repeatedly, quickly, in short succession, with minimum burden for the subject and with a modest quantity of equipment. This allows a drug to be fully characterized and profiled for analgesic effect which is especially useful for drugs with a novel or untested mechanism of action.

Validation of simple and inexpensive algometry using sphygmomanometer cuff and neuromuscular junction monitor with standardized laboratory algometer

Background and Aims:

The availability, ergonomics and economics prohibit the routine use of algometers in clinical practice and research by the anesthesiologists. A simple bedside technique of quantitative pain measurement would enable the routine use of algometry. We proposed to validate simple pain provocation using sphygmomanometer cuff and the electric stimulation of neuromuscular junction monitor (TOF-guard, Organon Teknika) to measure pain against a standardized laboratory pressure algometer.

Material and Methods:

Pain detection threshold (Pdt) and pain tolerance threshold (Ptt) were measured in forty healthy volunteers of both genders, using the above three techniques. All measurements were repeated three times. The co-efficient of inter-rater reliability (or consistency) between three independent measurements obtained from each of the techniques was determined by Cronbach's co-efficient alpha (α C). The correlation between the mean Pdt and Ptt values recorded by standardized algometer and the sphygmomanometer technique and nerve stimulator technique was performed using Pearson Correlation. An r >0.5 and a two-tailed significance of <0.05 were considered as good correlation between the standardized algometer and the tested techniques.

Results:

There was a good inter-rater reliability (α C > 0.7) for the three techniques. There was a good correlation with r >0.65 (P < 0.001) between the measurements of standardized pressure algometer and the two techniques being tested as alternatives for algometer to measure pain.

Conclusion:

The sphygmomanometer cuff technique and electrical stimulation with the peripheral nerve stimulator to measure pain threshold and tolerance provide a simple, efficient, repeatable measure of pain intensity and can be used as suitable alternatives to standard algometers.

Cornea nerve fiber quantification and construction of phenotypes in patients with fibromyalgia

Cornea confocal microscopy (CCM) is a novel non-invasive method to detect small nerve fiber pathology. CCM generally correlates with outcomes of skin biopsies in patients with small fiber pathology. The aim of this study was to quantify the morphology of small nerve fibers of the cornea of patients with fibromyalgia in terms of density, length and branching and further phenotype these patients using standardized quantitative sensory testing (QST). Small fiber pathology was detected in the cornea of 51% of patients: nerve fiber length was significantly decreased in 44% of patients compared to age- and sex-matched reference values; nerve fiber density and branching were significantly decreased in 10% and 28% of patients. The combination of the CCM parameters and sensory tests for central sensitization, (cold pain threshold, mechanical pain threshold, mechanical pain sensitivity, allodynia and/or windup), yielded four phenotypes of fibromyalgia patients in a subgroup analysis: one group with normal cornea morphology without and with signs of central sensitization, and a group with abnormal cornea morphology parameters without and with signs of central sensitization. In conclusion, half of the tested fibromyalgia population demonstrates signs of small fiber pathology as measured by CCM. The four distinct phenotypes suggest possible differences in disease mechanisms and may require different treatment approaches.

Cost-Saving Early Diagnosis of Functional Pain in Nonmalignant Pain: A Noninferiority Study of Diagnostic Accuracy

Objectives. We compared two index screening tests for early diagnosis of functional pain: pressure pain measurement by electronic diagnostic equipment, which is accurate but too specialized for primary health care, versus peg testing, which is cost-saving and more easily manageable but of unknown sensitivity and specificity. Early distinction of functional (altered pain perception; nervous sensitization) from neuropathic or nociceptive pain improves pain management. Methods. Clinicians blinded for the index screening tests assessed the reference standard of this noninferiority diagnostic accuracy study, namely, comprehensive medical history taking with all previous findings and treatment outcomes. All consenting patients referred to a university hospital for nonmalignant musculoskeletal pain participated. The main analysis compared the receiver operating characteristic (ROC) curves of both index screening tests. Results. The area under the ROC curve for peg testing was not inferior to that of electronic equipment: it was at least 95% as large for finger measures (two-sided p = 0.038) and at least equally as large for ear measures (two-sided p = 0.003). Conclusions. Routine diagnostic testing by peg, which is accessible for general practitioners, is at least as accurate as specialized equipment. This may shorten time-to-treatment in general practices, thereby improving the prognosis and quality of life.

Changes in Pain Sensitivity and Pain Modulation During Oral Opioid Treatment: The Impact of Negative Affect

OBJECTIVE

Opioids are frequently prescribed for chronic low back pain (CLBP), but there are broad individual differences in the benefits and risks of opioid therapy, including the development opioid-induced hyperalgesia. This study examined quantitative sensory testing (QST) data among a group of CLBP patients undergoing sustained oral opioid treatment. We investigated whether individual differences in psychological characteristics were related to opioid-induced changes in pain perception and pain modulation.

DESIGN

The six-month, open-label trial evaluated patients with low to high levels of negative affect (e.g., symptoms of distress, depression and anxiety); participants underwent QST at baseline (prior to initiating treatment) and during oral opioid treatment.

SETTING

A chronic pain management center.

PATIENTS

The 31 study participants had chronic discogenic back pain, with a pain intensity rating >3/10. Participants were divided into groups with high vs. low levels of Negative Affect (NA).

RESULTS

In the previously-published manuscript describing the clinical outcomes of the trial, high NA patients achieved only about half of the analgesic effect observed in the low NA group (Wasan AD, Michna E, Edwards RR, et al. Psychiatric comorbidity is associated prospectively with diminished opioid analgesia and increased opioid misuse in patients with chronic low back pain. Anesthesiology 2015;123:861-72). The QST findings reported here suggested that tolerance to experimental (cold pressor) pain and conditioned pain modulation tended to decrease in the high NA group over the course of opioid treatment, while temporal summation of mechanical pain declined in the low NA group.

CONCLUSIONS

These results reveal that while the low NA group seemed to exhibit a generally adaptive, analgesic pattern of changes during opioid management, the high NA group showed a pattern more consistent with opioid-induced hyperalgesic processes. A greater susceptibility to hyperalgesia-promoting changes in pain modulation among patients with high levels of distress may contribute to a lower degree of benefit from opioid treatment in high NA patients.

Fixed orthodontic appliances cause pain and disturbance in somatosensory function

This study aimed to assess the short-term effects of orthodontic pain on quantitative sensory testing (QST) in subjects receiving fixed orthodontic treatment. Twenty patients and 12 healthy volunteers (as controls) participated. All 20 patients had bonded AO self-ligating brackets, with a 0.014 super elastic nickel-titanium arch wire placed in the brackets. Pain [self-reported on a visual analog scale (VAS)], and thermal and mechanical thresholds, were tested at six time points--before (baseline), and 2 h, 24 h, 7 d, 14 d, and 30 d after, force application--in the treatment group. The attached gingiva adjacent to the left upper central incisor (21 gingiva) was hypersensitive to cold stimuli (i.e. increased cold detection thresholds were detected) in the treatment group. The pressure pain thresholds of the left upper central incisor (21) and 21 gingiva were significantly reduced. Our results suggest clear signs of sensitization of the trigeminal nociceptive system up to 1 month after force application and orthodontic pain. Quantitative assessment of somatosensory function may help to provide a better understanding and profiling of the underlying neurobiological mechanisms related to orthodontic pain.

A low cortisol response to stress is associated with musculoskeletal pain combined with increased pain sensitivity in young adults: a longitudinal cohort study

Background

In this study, we investigated whether an abnormal hypothalamic-pituitary-adrenal (HPA) axis response to psychosocial stress at 18 years of age is associated with musculoskeletal (MS) pain alone and MS pain combined with increased pain sensitivity at 22 years of age.

Methods

The study sample included 805 participants from the Western Australian Pregnancy Cohort (Raine) Study who participated in the Trier Social Stress Test (TSST) at age 18 years. Number of pain sites, pain duration, pain intensity and pain frequency were assessed at age 22 to measure severity of MS pain. Cold and pressure pain thresholds were determined at age 22. Group-based trajectory modeling was applied to establish cortisol response patterns based on the TSST. Logistic regression was used to study the association of TSST patterns with MS pain alone and MS pain combined with increased cold or pressure pain sensitivity, adjusted for relevant confounding factors. All analyses were stratified by sex.

Results

The mean (standard deviation) age during the TSST was 18.3 (0.3) years, and during MS pain assessment it was 22.2 (0.6). Forty-five percent of the participants were female. Three cortisol response patterns were identified, with cluster 1 (34 % of females, 21 % of males) reflecting hyporesponse, cluster 2 (47 %, 54 %) reflecting intermediate response and cluster 3 (18 %, 24 %) reflecting hyperresponse of the HPA axis. MS pain was reported by 42 % of females and 33 % of males at age 22 years. Compared with females in cluster 2, females in cluster 1 had an increased likelihood of having any MS pain (odds ratio 2.3, 95 % confidence interval 1.0–5.0) and more severe MS pain (2.8, 1.1–6.8) if their cold pain threshold was above the median. In addition, females in cluster 1 had an increased likelihood (3.5, 1.3–9.7) of having more severe MS pain if their pressure pain threshold was below the median. No statistically significant associations were observed in males.

Conclusions

This study suggests that a hyporesponsive HPA axis at age 18 years is associated with MS pain at 22 years in young females with increased pain sensitivity.