Pain trajectories and neuropathic pain symptoms following lung cancer surgery: A prospective cohort study.

BACKGROUND: Persistent postsurgical pain (PPSP) after lung cancer surgery is common and current definitions are based on evaluations at a single time point after surgery. Pain intensity and symptoms may however fluctuate and change over time, and be impacted by multiple and shifting factors. Studies of postoperative recovery patterns and transition from acute to chronic pain are needed for further investigation of preventive measures and treatments to modify unfavourable recovery paths. METHODS: In this explorative study, 85 patients undergoing surgery due to either presumptive or confirmed lung cancer reported pain intensities bi-monthly for 12 months. Pain trajectories during recovery were investigated, using group-based trajectory modelling. Associations with possible risk factors for PPSP, including clinical variables and anxiety and depression score (HADS), were also explored. RESULTS: A trajectory model containing three 12-month pain recovery groups was computed. One group without PPSP fully recovered (50%) within two to three months. Another group with mild-intensity PPSP followed a protracted recovery trajectory (37%), while incomplete recovery was observed in the last group (13%). Acute postoperative pain and younger age were associated with a less favourable recovery trajectory. More neuropathic pain symptoms were observed in patients with incomplete recovery. CONCLUSIONS: Three clinically relevant recovery trajectories were identified, based on comprehensive pain tracking. Higher acute postoperative pain intensity was associated with an unfavourable pain recovery trajectory. SIGNIFICANCE STATEMENT: Understanding the transition from acute to chronic postoperative pain and identifying preoperative risk factors is essential for the development of targeted treatments and the implementation of preventive measures. This study (1) identified distinct recovery trajectories based on frequent pain assessment follow-ups for 12 months after surgery and (2) evaluated risk factors for unfavourable postoperative pain recovery paths. Findings suggest that early higher postoperative pain intensity is associated with an unfavourable long-term recovery path.

Quantitative sensory testing, psychological profiles and clinical pain in patients with psoriatic arthritis and hand osteoarthritis experiencing pain of at least moderate intensity.

BACKGROUND: Chronic pain is the hallmark symptom of joint diseases. This study examined the differences in quantitative sensory testing between patients with psoriatic arthritis (PsA), hand osteoarthritis (hand-OA) and a pain-free control group and differences between patients with and without concomitant fibromyalgia (cFM). METHODS: All patients and pain-free controls were assessed using pressure pain thresholds (PPT), temporal summation of pain (TSP), conditioned pain modulation (CPM) and clinical pain intensities. Psychological distress was assessed with the Hospital Anxiety and Depression Scale, Pain Catastrophizing Scale, and Pittsburgh Sleep Quality Index. Disability was assessed with the Health Assessment Questionnaire and pain quality with the painDETECT questionnaire. cFM was identified using the revised 2016 American College of Rheumatology diagnostic criteria. RESULTS: Patients with hand-OA (n = 75) or PsA (n = 58) had statistically significant lower PPTs and CPM, greater TSP, and higher scores of psychological distress (p < 0.05) than controls (n = 20). Patients with cFM (58%) had higher scores of depression (p = 0.001), anxiety (p = 0.004), catastrophizing (p = 0.012), disability (p < 0.001), higher painDETECT score (p = 0.001), TSP (p = 0.027), and reduced sleep quality (p = 0.021) when compared to patients without cFM. CONCLUSION: Patients with hand-OA and PsA exhibited signs of pain sensitization and a higher degree of psychological distress and disability than pain-free individuals. Patients with cFM had greater TSP, painDETECT score, disability, catastrophizing, and reduced sleep quality, than patients without, indicating greater degree of pain sensitization, psychological burden, and disability. STATEMENT OF SIGNIFICANCE: This paper shows that a significant proportion of patients with hand osteoarthritis and psoriatic arthritis with moderate pain intensity have significantly increased signs of pain sensitization and markers of psychological distress. A large proportion of these patients fulfil the criteria for concomitant fibromyalgia and these patients show even greater propensity towards pain sensitization and psychological distress.

The evolving landscape of publishing in the field of pain: An automated bibliometric analysis from 1975 to 2020.

BACKGROUND: The aims of this bibliometric analysis were (1) a longitudinal analysis of the publication landscape in the field of pain (1975-2020) and (2) to characterize the overall publication profiles for two selected journals: European Journal of Pain and PAIN® utilizing an automated approach. METHODS: Database searches in Scopus extracted all journals with 'pain' in their title. For the two specific journals, papers were manually/automatically profiled into preclinical, human and translational studies. RESULTS: A gross list of 64 journals in the field of pain consisting of both active and ceased journals in Scopus were included in this analysis which identified 62,565 papers with approximately 4000 papers published/year. These papers include 2759 and 9156 papers in Eur. J. Pain and PAIN®, respectively. Currently, there are 24 active 'pain' journals. Authors/paper increase from 2 to 7 indicating a development from mono-disciplinary to multi-disciplinary studies. The overall publication profiles assessing preclinical, human (experimental/clinical) and translational papers in Eur. J. Pain and PAIN® were almost similar (14%, 75% and 10% versus 26%, 63% and 10%). Papers have changed over the years from mono-disciplinary studies (e.g. behavioural studies) to multi-disciplinary studies (e.g. combined behavioural and cell studies). After optimization, the search model matched the manual screening by 100%, 98% and 96% for the preclinical, clinical and healthy volunteer categories. CONCLUSIONS: Over the last 45 years, more than 60,000 pain-related papers have been published. Papers develop over the years from mono-disciplinary to multi-disciplinary studies. The overall publication profile including preclinical, human (experimental/clinical) and translational papers was almost similar in Eur. J. Pain and PAIN®. SIGNIFICANCE: The bibliometric analysis of a pain journal provides information on which specific areas of research are published, how this may have changed over the years and how a journal is positioned compared with other journals in the field.

Subgrouping of facilitatory or inhibitory conditioned pain modulation responses in patients with chronic knee pain. Explorative analysis from a multicentre trial.

BACKGROUND: Facilitatory and inhibitory conditioned pain modulation (CPM) responses are observed in healthy volunteers and chronic pain patients, but the clinical implications for phenotyping are unknown. This study aimed to subgroup and compare chronic knee pain patients according to their CPM responses. METHODS: This explorative, cross-sectional study included 127 patients with chronic knee pain (osteoarthritis or following total knee arthroplasty). Individual CPM responses were categorized as facilitatory (test stimuli pain intensity increased when conditioning stimuli were applied), as inhibitory (test stimuli pain intensity decreased) or as no change (defined as less than 5.3% change in pain intensity). Outcomes were clinical pain intensities, temporal summation, widespread pain, self-reported physical function, PainDETECT questionnaire and Pain Quality Assessment Scale. Data were analysed as comparisons between the inhibitory and the facilitatory groups and using multivariate linear regression models. RESULTS: Fifty-four patients had facilitatory CPM responses, 49 had inhibitory CPM responses, and 24 showed no change in CPM response. A between-group difference was observed for self-reported physical function, with the facilitatory CPM group reporting better function (54.4 vs. 46.0, p = 0.028) and the facilitatory CPM group reported more deep pain sensations (3.2 vs. 2.0, p = 0.021). The remaining outcomes showed no between-group differences. Higher clinical pain intensity and facilitated temporal summation were associated in the facilitated CPM group but not in the inhibitory CPM group. CONCLUSION: These explorative findings indicated that quantitative clinical and experimental differences exist between facilitatory or inhibitory CPM responses in a chronic knee pain patient population. Differences in patients' CPM responses should be further investigated to unravel possible clinical importance. SIGNIFICANCE: Our findings confirm that conditioned pain modulation consist of inhibitory and facilitatory responders among a patient population with chronic knee pain. This explorative study indicates that patients with either facilitatory or inhibitory conditioned pain modulation could exhibit differences in pain outcomes. Subgrouping of chronic pain patients depending on individual conditioned pain modulation responses could be considered in phenotyping patients prior to inclusion in clinical trials or used for personalizing the management regime.

Reflections from the 2021 OARSI clinical trial symposium: Considerations for understanding biomarker assessments in osteoarthritis drug development - Should future studies focus on disease activity, rather than status?

Objective: Osteoarthritis (OA) is heterogeneous disease, for which drug development has proven to be challenging, both facilitated and hampered by changing guidelines. This is evident by the current lack of approved treatments, which improve joint function and delay joint failure. There is a need to bring together key stakeholders to discuss, align and enhance the processes for OA drug development to benefit patients. Design: To facilitate drug development, the Osteoarthritis Research Society International (OARSI) initiated a series of annual clinical trials symposia (CTS). The aim of these symposia was to bring together academics, translational and clinical scientists, regulators, drug developers, and patient advocacy groups to share, refine and enhance the drug development process for the benefit of patients. Results: OARSI is now considered the leading organization to facilitate open dialogue between all these stakeholders, in the intersection of understanding of the pathologies and drug development. Clearly, such a pivotal task needs an annual forum to allow stakeholders to share and discuss information, as possible solutions are joint efforts rather than a single stakeholder contribution. Conclusions: The main topic of the 2021 CTS was how to improve clinical studies to help patients through overcoming barriers to development of new disease modifying treatments for OA. One key aspect was the focus on definitions of disease activity, status and the definitions of "illness vs disease". There is a clear medical need to couple a given disease activity with the optimal intervention for the right patient.

Sensory, Motor, and Psychosocial Characteristics of Individuals With Chronic Neck Pain: A Case-Control Study.

OBJECTIVE: Given the complex and unclear etiology of neck pain, it is important to understand the differences in central sensitization as well as psychosocial factors in individuals with chronic neck pain and healthy controls. The purpose of this study was to benchmark differences in central sensitization, psychosocial factors, and range of motion between people with nonspecific chronic neck pain and healthy controls and to analyze the correlation between pain intensity, neck disability, and psychosocial factors in people with chronic neck pain. METHODS: Thirty individuals with chronic neck pain and 30 healthy controls were included in this case-control study. Outcome measures were as follows: central sensitization (pressure pain threshold, temporal summation, and conditioned pain modulation), psychosocial factors (depressive symptoms, pain catastrophizing, and quality of life), and active cervical range of motion. RESULTS: People with neck pain had lower local pressure pain threshold, a decrease in conditioned pain modulation, more depressive symptoms, greater pain catastrophizing, lower quality of life, and reduced range of motion for neck rotation when compared with healthy controls. In people with neck pain, moderate correlations were observed between pain intensity and quality of life (ρ = -0.479), disability and pain catastrophizing (ρ = 0.379), and disability and quality of life (ρ = -0.456). CONCLUSIONS: People with neck pain have local hyperalgesia, impaired conditioning pain modulation, depressive symptoms, pain catastrophizing, low quality of life, and reduced active range of motion during neck rotation, which should be taken into account during assessment and treatment. IMPACT: This study shows that important outcomes, such as central sensitization and psychosocial factors, should be considered during assessment and treatment of individuals with nonspecific chronic neck pain. In addition, pain intensity and neck disability are correlated with psychosocial factors.

Quantitative sensory testing in feline osteoarthritic pain - a systematic review and meta-analysis.

Quantitative sensory testing (QST) is a psychophysical test used to quantify somatosensory sensation under normal or pathological conditions including osteoarthritis (OA). OBJECTIVE: This study aimed to conduct a systematic review and meta-analysis of studies using QST in healthy and osteoarthritic cats, registered at Systematic Review Research Facility (#26-06-2017). DESIGN: Hierarchical models with random intercepts for each individual study extracted through the systematic review were fit to subject-level data; QST measures were contrasted between healthy and osteoarthritic cats. Four bibliographic databases were searched; quality and risk of bias assessment were performed using pre-established criteria. RESULTS: Six articles were included; most were of high quality and low risk of bias. Punctate tactile threshold (n = 70) and mechanical temporal summation (n = 35) were eligible for analysis. Cats with OA have lower punctate tactile threshold [mean difference (95%HDI): -44 (-60; -26) grams] and facilitated temporal summation of pain [hazard ratio (95%HDI): 5.32 (2.19; 14) times] when compared with healthy cats. The effect of sex and body weight on sensory sensitivity remained inconclusive throughout all analyses. Due to the correlation between age and OA status, it remains difficult to assess the effect of OA on sensory sensitivity, independently of age. CONCLUSIONS: Clear and transparent reporting using guidelines are warranted. Similar to people, centralized sensitization is a feature of OA in cats. Future studies should try to elucidate the age effect on feline OA. Research with natural OA in cats is promising with potential to benefit feline health and welfare, and improve translatability to clinical research.

Cost-effectiveness of 12 weeks of supervised treatment compared to written advice in patients with knee osteoarthritis: a secondary analysis of the 2-year outcome from a randomized trial.

OBJECTIVE: To assess the 24-month cost-effectiveness of supervised treatment compared to written advice in knee osteoarthritis (OA). DESIGN: 100 adults with moderate-severe OA not eligible for total knee replacement (TKR) randomized to a 12-week individualized, supervised treatment (exercise, education, diet, insoles and pain medication) or written advice. Effectiveness was measured as change in quality-adjusted life years (QALYs) from baseline to 24 months, including data from baseline, 3, 6, 12 and 24 months, while healthcare costs and transfer payments were derived from national registries after final follow-up. Incremental costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs) were calculated. A sensitivity analysis resampling existing data was conducted and the probability of cost-effectiveness was estimated using a 22,665 Euros/QALY threshold. In a sensitivity analysis, cost-effectiveness was calculated for different costs of the supervised treatment (actual cost in study; cost in private practice; and in-between cost). RESULTS: Average costs were similar between groups (6,758 Euros vs 6,880 Euros), while the supervised treatment were close to being more effective (incremental effect (95% CI) of 0.075 (-0.005 to 0.156). In the primary analysis excluding deaths, this led the supervised treatment to be cost-effective, compared to written advice. The sensitivity analysis demonstrated that the results were sensitive to changes in the cost of treatment, but in all scenarios the supervised treatment was cost-effective (ICERs of 6,229 to 20,688 Euros/QALY). CONCLUSIONS: From a 24-month perspective, a 12-week individualized, supervised treatment program is cost-effective compared to written advice in patients with moderate-severe knee OA not eligible for TKR. TRIAL REGISTRATION: ClinicalTrials.gov number: NCT01535001.

Acquisition of a simple motor skill: task-dependent adaptation and long-term changes in the human soleus stretch reflex.

Changing the H reflex through operant conditioning leads to CNS multisite plasticity and can affect previously learned skills. To further understand the mechanisms of this plasticity, we operantly conditioned the initial component (M1) of the soleus stretch reflex. Unlike the H reflex, the stretch reflex is affected by fusimotor control, comprises several bursts of activity resulting from temporally dispersed afferent inputs, and may activate spinal motoneurons via several different spinal and supraspinal pathways. Neurologically normal participants completed 6 baseline sessions and 24 operant conditioning sessions in which they were encouraged to increase (M1up) or decrease (M1down) M1 size. Five of eight M1up participants significantly increased M1; the final M1 size of those five participants was 143 ± 15% (mean ± SE) of the baseline value. All eight M1down participants significantly decreased M1; their final M1 size was 62 ± 6% of baseline. Similar to the previous H-reflex conditioning studies, conditioned reflex change consisted of within-session task-dependent adaptation and across-session long-term change. Task-dependent adaptation was evident in conditioning session 1 with M1up and by session 4 with M1down. Long-term change was evident by session 10 with M1up and by session 16 with M1down. Task-dependent adaptation was greater with M1up than with the previous H-reflex upconditioning. This may reflect adaptive changes in muscle spindle sensitivity, which affects the stretch reflex but not the H reflex. Because the stretch reflex is related to motor function more directly than the H reflex, M1 conditioning may provide a valuable tool for exploring the functional impact of reflex conditioning and its potential therapeutic applications. NEW & NOTEWORTHY Since the activity of stretch reflex pathways contributes to locomotion, changing it through training may improve locomotor rehabilitation in people with CNS disorders. Here we show for the first time that people can change the size of the soleus spinal stretch reflex through operant conditioning. Conditioned stretch reflex change is the sum of task-dependent adaptation and long-term change, consistent with H-reflex conditioning yet different from it in the composition and amount of the two components.

Antipruritic effects of transient heat stimulation on histaminergic and nonhistaminergic itch.

BACKGROUND: Chronic itch is notoriously difficult to treat. Counterstimuli are able to inhibit itch, but this principle is difficult to apply in clinical practice, and the mechanisms behind counterstimulation-induced itch suppression in humans are unclear. OBJECTIVES: Firstly, to analyse the stimulus-response effects of transient heat stimuli on histaminergic and nonhistaminergic itch, and secondly, to investigate whether the antipruritic effect depends on homotopic (peripheral mediation) or heterotopic (central mediation) counterstimulation relative to the itch provocation site. METHODS: Eighteen healthy volunteers participated (eight female, mean age 25·7 ± 0·8 years). Itch was evoked on premarked areas of the volar forearms, by either histamine (1% solution) or cowhage (35-40 spicules). In addition to the itch provocations (experiment 1), 5-s homotopic heat stimuli at 32, 40, 45 or 50 °C were applied. In experiment 2, heat stimuli were applied either homotopically, intrasegmentally (next to the provocation site) or extrasegmentally (dorsal forearm). Itch intensity was evaluated throughout the procedures using a digital visual analogue scale. RESULTS: Homotopic counterstimuli inhibited histaminergic itch by 41·3% at 45 °C (P < 0·01) and by 76·7% at 50 °C (P < 0·001). Cowhage-induced itch was less prone to counterstimulation and was significantly diminished only at 50 °C, by 43·6% (P = 0·009). Counterstimulations applied heterotopically were not able to inhibit itch significantly. CONCLUSIONS: Itch pathway-specific effects of counterstimuli were observed between homo- and heterotopic stimulation. Histaminergic itch was robustly inhibited by short-term homotopic noxious heat stimuli for up to 10 min. Nonhistaminergic itch was only weakly inhibited. The inhibitory effects exerted by the short-term heat stimuli only occurred following homotopic counterstimulation.

Potential diagnostic value of a type X collagen neo-epitope biomarker for knee osteoarthritis.

OBJECTIVE: Phenotypic changes of chondrocytes toward hypertrophy might be fundamental in the pathogenesis of osteoarthritis (OA), of which type X collagen (Col10) is a well-known marker. The purpose was to develop a specific immunoassay for blood quantification of a newly identified neo-epitope of type Col10 to assess its diagnostic value for radiographic knee OA. METHODS: A neo-epitope of Col10 was identified in urine samples from OA patients. A monoclonal antibody against the neo-epitope was produced in Balb/C mice. The enzyme responsible for the cleavage was identified. Immunohistochemical detection of this neo-epitope was performed on human OA cartilage. An immunoassay (Col10neo) was developed and quantified in two clinical studies: the C4Pain-003 and the NYU OA progression study. Receiver operating characteristic curve (ROC) curve analysis was carried out to evaluate the discriminative power of Col10neo between OA and rheumatoid arthritis (RA). RESULTS: A neo-epitope specific mAb was produced. The Cathepsin K-generated neo-epitope was localized to the pericellular matrix of chondrocytes, while its presence was extended and more prominent in superficial fibrillation in the cartilage with advanced degradation. In the C4Pain study, a higher level of Col10neo was seen in subjects with greater KL grade. The group of the highest tertile of Col10neo included more subjects with KL3-4. In the NYU study, Col10neo was statistically higher in OA than control or RA. ROC curve analysis revealed area under the curve was 0.88 (95% CI 0.81-0.94). CONCLUSION: Our findings indicate that Col10neo linked to hypertrophic chondrocytes could be used as a diagnostic biochemical marker for knee OA.

Electrical stimulation for evoking offset analgesia: A human volunteer methodological study.

BACKGROUND: Offset analgesia (OA) is a disproportionally large decrease in the pain perception in response to a small decrease in the stimulation intensity. Traditionally, heat stimulation has been used to evoke OA. The aim of this study was to investigate whether OA could be evoked by electrical stimulation. METHODS: Healthy volunteers (N = 24) underwent two OA-experimental sessions consisting of heat stimuli intensities of 48-49-48 °C (traditional OA-paradigm) and electrical stimuli at 150%-180%-150% of the electrical pain perception (EPP) threshold. The three stimuli were delivered for 5 s (STIM1), 5 s (STIM2) and 20 s (STIM3), respectively. The sessions were randomized to the dominant or nondominant volar forearm. Two control sessions were performed with 30 s constantly heat (48 °C) and electrical stimuli (150% of the EPP) (CONTROL-STIM). In all sessions, the pain intensities were constantly rated on a Visual Analog Scale (VAS, 0-10). RESULTS: Significantly reduced STIM3 VAS ratings as compared to the CONTROL-STIM were reported for heat (1.81 ± 0.54; p < 0.001) and electrical (2.12 ± 0.42; p < 0.001) stimuli. The degrees of OA produced by heat and electrical stimuli were similar. A significantly positive correlation was found between thermal and electrical OA-effects (r = 0.48, p < 0.02). CONCLUSIONS: These findings demonstrate that electrical stimulation can elicit significant OA in humans indicating that the peripheral receptors can be bypassed and still evoke OA. Application of the electrical OA model may be of interest for further basic and clinical investigations as a potential new biomarker for central pain inhibition and provide the option to back-translate the technology to animals to understand the underlying neurobiology. SIGNIFICANCE: Electrical stimulation can elicit offset analgesia in humans, indicating that this perceptual modification can be obtained even bypassing peripheral receptors.

Total knee replacement and non-surgical treatment of knee osteoarthritis: 2-year outcome from two parallel randomized controlled trials.

OBJECTIVES: To compare 2-year outcomes of total knee replacement (TKR) followed by non-surgical treatment to that of non-surgical treatment alone and outcomes of the same non-surgical treatment to that of written advice. DESIGN: In two randomized trials, 200 (mean age 66) adults with moderate to severe knee osteoarthritis (OA), 100 eligible for TKR and 100 not eligible for TKR, were randomized to TKR followed by non-surgical treatment, non-surgical treatment alone, or written advice. Non-surgical treatment consisted of 12 weeks of supervised exercise, education, dietary advice, use of insoles, and pain medication. The primary outcome was the mean score of the Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales, covering pain, symptoms, activities of daily living (ADL), and quality of life (QOL). RESULTS: Patients randomized to TKR had greater improvements than patients randomized to non-surgical treatment alone (difference of 18.3 points (95% CI; 11.3 to 25.3)), who in turn improved more than patients randomized to written advice (difference of 7.0 points (95% CI; 0.4 to 13.5)). Among patients eligible for TKR, 16 (32%) from the non-surgical group underwent TKR during 2 years and among those initially ineligible, seven patients (14%) from the non-surgical group and ten (20%) from the written advice group underwent TKR. CONCLUSIONS: TKR followed by non-surgical treatment is more effective on pain and function than non-surgical treatment alone, which in turn is more effective than written advice. Two out of three patients with moderate to severe knee OA eligible for TKR delayed surgery for at least 2 years following non-surgical treatment. TRIAL REGISTRATION: ClinicalTrials.gov numbers NCT01410409 and NCT01535001.

Aggrecanase degradation of type III collagen is associated with clinical knee pain.

There is a lack of biochemical markers for non-invasive and objective assessment of symptomatic osteoarthritis (OA). Aggrecanase activity has been shown to be associated with joint deterioration and symptomatic disease through the degradation of extracellular matrix proteins, such as type III collagen. Our study aimed to identify and develop a novel biomarker by measuring an aggrecanase-mediated type III collagen neoepitope, and correlate levels of this biomarker with OA joint pain. Mass spectrometric analysis of purified type III collagen, degraded by the aggrecanase A Disintigrin and Metalloproteinase with Thrombospondin motif (ADAMTS), revealed a fragment generated by ADAMTS-1, -4 and -8. A monoclonal antibody was raised against the neoepitope of this fragment (COL3-ADAMTS) and a competitive ELISA was developed and tested; using serum samples from a cross-sectional cohort of patients with different degrees of knee OA (n = 261). The COL3/ADAMTS ELISA was technically robust and specific for the ADAMTS-1, -4 and -8 generated neoepitope. COL3/ADAMTS was released form cytokine stimulated synovial cultures, indicating a biologic link between the marker and synovium. In OA patients, serum COL3/ADAMTS was independently associated with pain scores (rho = -0.13-0.17, p < 0.05). This association was associated significantly with the presence of radiographic OA. Together, these data indicate that COL3/ADAMTS could be a marker of early osteoarthritis and the underlining pathology.

Predicting drug efficacy in chronic low back pain by quantitative sensory tests.

BACKGROUND: Drugs are prescribed for chronic low back pain without knowing in advance whether a patient will respond to them or not. Quantitative sensory tests (QST) can discriminate patients according to sensory phenotype, possibly reflecting underlying mechanisms of pain processing. QST may therefore be a screening tool to identify potential responders to a certain drug. The aim of this study was to investigate whether QST can predict analgesic effects of oxycodone, imipramine and clobazam in chronic low back pain. METHODS: Oxycodone 15 mg (n = 50), imipramine 75 mg (n = 50) and clobazam 20 mg (n = 49) were compared to active placebo tolterodine 1 mg in a randomized, double-blinded, crossover fashion. Electrical, pressure and thermal QST were performed at baseline and after 1 and 2 h. Pain intensity was assessed on a 0-10 numeric rating scale every 30 min for up to 2 h. The ability of baseline QST to predict pain reduction after 2 h was analysed using linear mixed models. Genetic variants of drug-metabolizing enzymes and genes affecting pain sensitivity were examined as covariables. RESULTS: No predictor of analgesic effect was found for oxycodone and clobazam. Thermal QST was associated with analgesic effect of imipramine: patients more sensitive to heat or cold were more likely to experience an effect of imipramine. Pharmacogenetic variants and pain-related candidate genes were not associated with drug efficacy. CONCLUSIONS: Thermal QST have the potential to predict imipramine effect in chronic low back pain. Oxycodone and clobazam effects could not be predicted by any of the selected QST or genetic variants. SIGNIFICANCE: Predicting drug efficacy in chronic low back pain remains difficult. There is some evidence that patients more sensitive to heat and cold pain respond better to imipramine.

Pain and sensitization after total knee replacement or nonsurgical treatment in patients with knee osteoarthritis: Identifying potential predictors of outcome at 12 months.

BACKGROUND: This study is a secondary analysis of 12-month follow-ups from two parallel, randomized controlled trials (RCT) in painful knee osteoarthritis patients. RCT1: Total knee replacement (TKR) followed by nonsurgical treatment compared with nonsurgical treatment. RCT2: Nonsurgical treatment compared with usual care. The aims were to investigate (1) possible predictors of treatment outcome after TKR and nonsurgical interventions at 12 months, (2) associations between pain intensity and pressure pain thresholds (PPTs) (pain sensitization) at baseline and after 12 months and (3) possible gender differences. METHOD: Each RCT included 100 patients. Pain intensities, PPTs and number of painful sites were assessed at baseline and after 12 months. RESULTS: In all groups, pain improved and pain sensitization decreased. In RCT1, the TKR group had the greatest improvements in pain. In RCT2 the nonsurgical group had the greatest improvement, with no between-group differences in PPTs. Lower PPTs at baseline predicted higher pain after TKR. Baseline pain intensity and PPT levels were associated with the number of painful sites. Subjects with the highest pain and lowest PPTs at baseline showed the largest relative improvement in pain and sensitization but were still experiencing highest absolute pain and lowest PPTs after 12 months (combined cohorts). CONCLUSION: Low PPTs at baseline predicted worse pain outcome after TKR, but did not predict outcome after nonsurgical interventions. The number of painful sites was weakly associated with pain and PPTs, and the higher pain/lower PPTs, the higher pain/lower PPTs at 12 months with females showing the lowest PPT values. SIGNIFICANCE: Human experimental pain assessment was used to assess the degree of pain sensitization in patients with painful knee osteoarthritis. High sensitization before TKR predicted worse outcome. Outcome after nonsurgical interventions could not be predicted.

Offset analgesia: The role of peripheral and central mechanisms.

BACKGROUND: Offset Analgesia (OA) can be evoked by a three-heat-stimulus train (T1-T2-T3), with T1 (5 s) and T3 (20 s) having the same temperature (e.g. 48 °C) and T2 (5 s) being slightly higher (1-3 °C). OA is defined as a disproportional pain reduction caused by the slight temperature decrease from T2 to T3. As the pain modulatory mechanisms behind OA are still poorly understood, the current study aimed to investigate the role of peripheral and central mechanisms by applying heat stimuli to the same location and to different unilateral and bilateral locations. METHOD: Young healthy volunteers participated in the study. A 'standard-OA' paradigm (48-49-48 °C) was applied to the non-dominant volar forearm (T1-T2-T3 applied on the same location). 'Unilateral-OA' trials were applied on three different locations of the non-dominant volar forearm (the same dermatome). 'Bilateral-OA' trials were applied by shifting T1-T2-T3 between dominant and non-dominant volar forearms. A constant stimulus of 48 °C was applied as control for the evoked pain. The pain intensities were continuously recorded using an electronic visual analogue scale. RESULTS: The largest pain intensity reduction was reported for the 'standard-OA' paradigm (p < 0.001) compared with the control stimulus. Both 'Unilateral-OA' and 'Bilateral-OA' trials caused a significant pain reduction (p < 0.05) compared with the control; however, the pain reduction was less than that evoked by 'standard-OA' (p < 0.05). CONCLUSION: This study showed that OA could be elicited when the stimuli were applied both to the same and to different locations (ipsi- and contralateral) indicating that peripheral as well as central mechanisms are involved in mediating OA. SIGNIFICANCE: This study investigated offset analgesia by applying thermal painful stimuli to the ipsi- and bilateral forearms in healthy subjects and found that both peripheral and central mechanisms seem to mediate offset analgesia.

γ-Aminobutyric acid (GABA) oral rinse reduces capsaicin-induced burning mouth pain sensation: An experimental quantitative sensory testing study in healthy subjects.

BACKGROUND: In burning mouth patients, analgesia after oral administration of clonazepam may result from modulation of peripheral γ-aminobutyric acid (GABA) receptors. METHODS: The effect of oral administration of test solutions (water, 0.5 mol/L or 0.05 mol/L GABA, 1% lidocaine) was investigated for the amelioration of pain and sensitivity induced by application of capsaicin (1%, 2 min) to the tongue of thirty healthy male and female subjects in this four-session, randomized, placebo-controlled, double-blinded, cross-over study. Intra-oral quantitative sensory testing was used to assess cold (CDT), warm (WDT) and mechanical (MDT) detection thresholds as well as mechanical (MPT) and heat (HPT) pain thresholds. Capsaicin-induced pain intensity was continuously rated on a 0-10 electronic visual analogue scale (VAS). The area under the VAS curve (VASAUC) after rinsing was calculated for each solution. RESULTS: Capsaicin application on the tongue evoked burning pain with a peak of 4.8/10, and significantly increased CDT and MDT while significantly decreasing WDT, HPT, and MPT. The VASAUC was significantly smaller after oral rinse with 0.05 mol/L GABA, 0.5 mol/L GABA, and 1% lidocaine than after oral rinse with water. Rinse with 0.5 mol/L or 0.05 mol/L GABA were similarly effective in decreasing VASAUC. Rinsing with either 1% lidocaine, 0.5 mol/L or 0.05 mol/L GABA also significantly attenuated the effects of capsaicin on WDT and HPT in a treatment independent manner. There were no sex-related differences in these effects of GABA. CONCLUSIONS: Capsaicin-induced burning tongue pain and decreases in WDT and HPT can be ameliorated by rinsing the mouth with lidocaine and GABA solutions. SIGNIFICANCE: Rinsing the mouth with an oral GABA containing solution ameliorated burning pain and increased heat sensitivity produced by application of capsaicin to the tongue. This finding suggests that GABA can act as a local analgesic agent in the oral cavity.

Assessment and manifestation of central sensitisation across different chronic pain conditions.

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