Pathophysiology of pain

Biphasic Hormetic-like Effect of Lebecetin, a C-type Lectin of Snake Venom, on Formalin-induced Inflammation in Mice

BACKGROUND

Integrins, important extracellular matrix (ECM) receptor proteins, are affected by inflammation and can participate in the maintenance of many painful conditions. Although they are ubiquitous and changeable across all cell types, the roles of these cell adhesion molecules in pathological pain have not been fully explored.

OBJECTIVE

We evaluated the effects of the subcutaneous injection of lebecetin, a C-type lectin isolated from Macrovipera lebetina snake venom, previously reported to inhibit α5β1 and αv integrin activity, on different components of inflammation induced by the formalin administration in the hind paw of mice.

METHODS

The formalin-induced nocifensive behavior, edema, and histopathological changes in the hind paw associated with cytokine, iNOS, and COX2 expression, nociceptive-specific neuron activity, and microglial activation analysis in the spinal cord were evaluated in mice receiving vehicle or lebecetin pretreatment.

RESULTS

Lebecetin inhibited the nocifensive responses in the formalin test, related edema, and cell infiltration in the injected paw in a biphasic, hormetic-like, and dose-dependent way. According to that hormetic trend, a reduction in pro-inflammatory cytokines IL-6, IL-8, and TNF-alpha and upregulation of the anti-inflammatory cytokine IL-10 in the spinal cord were found with the lowest doses of lebecetin. Moreover, COX2 and iNOS expression in serum and spinal cord followed the same biphasic pattern of cytokines. Finally, nociceptive neurons sensitization and activated microglia were normalized in the dorsal horn of the spinal cord by lebecetin.

CONCLUSION

These findings implicate specific roles of integrins in inflammation and tonic pain, as well as in the related central nervous system sequelae.

Pain Education in the Management of Patients with Chronic Low Back Pain: A Systematic Review

New prospective of chronic low back pain (CLBP) management based on the biopsychosocial model suggests the use of pain education, or neurophysiological pain education, to modify erroneous conceptions of disease and pain, often influenced by fear, anxiety and negative attitudes. The aim of the study is to highlight the evidence on the outcomes of a pain education-oriented approach for the management of CLBP. The search was conducted on the Pubmed, Scopus, Pedro and Cochrane Library databases, leading to 2673 results until September 2021. In total, 13 articles published in the last 10 years were selected as eligible. A total of 6 out of 13 studies support a significant reduction in symptoms in the medium term. Disability is investigated in only 11 of the selected studies, but 7 studies support a clear reduction in the medium-term disability index. It is difficult to assess the effectiveness of the treatments of pain education in patients affected by CLBP, due to the multimodality and heterogeneity of the treatments administered to the experimental group. In general, methods based on pain education or on cognitive-behavioral approaches, in association with physical therapy, appear to be superior to physiotherapeutic interventions alone in the medium term.

A high-dosage microneedle for programmable lidocaine delivery and enhanced local long-lasting analgesia

Considering the staggering global prevalence of local pain affecting hundreds of million individuals, it is of great significance to develop advanced dosage forms or delivery systems for analgesic therapy to fulfill clinical applicability. In this study, a hydrogel microneedles (MNs) system made out of gelatin-methacryloyl (GelMA) was designed to deliver lidocaine hydrochloride (LiH) in a sustained manner, and the drug loading capacity of the GelMA MNs was increased considerably by using the backing layer reservoir. The in vitro and in vivo tests showed that the fabricated GelMA MNs are strong enough for reliable skin application, and achieve high drug delivery efficiency as compared with the commercial lidocaine patches. The Spared-nerve injury (SNI) model of rats was also prepared to test behavioral pain sensitivity in response to mechanical stimuli, which proved that the LiH/GelMA MNs can enhance and prolong the anesthetic effect of LiH. In addition, with biosafety evaluation in rats, the MNs treated site restored to normal appearance within several hours of application and no dermatosis-related side effects or behavior disorders were observed during the experiment. Together these results indicated that the use of GelMA MNs for transdermal delivery of LiH is an effective, safe and simple treatment method to provide a better choice for local long-lasting analgesia.

Effectiveness of Kinesiotaping in Reducing Postoperative Knee Edema and Pain Compared to Other Standard Treatments: A Critically Appraised Topic

Focused Clinical Question: Does the application of kinesiotape compared with standard treatments result in greater/faster postoperative edema reduction after total knee replacement or anterior cruciate ligament repair?Clinical Bottom Line: There was sufficient evidence to support the application of kinesiotape to reduce postoperative edema brought on by a total knee replacement or anterior cruciate ligament repair. Patients who received kinesiotaping, applied to the skin with a pattern to enhance lymphatic drainage, showed significant decreases in postoperative knee circumference measurements and pain levels. Kinesiotaping application under these acute conditions offers an evidence-based approach for clinicians to optimize the physiological environment and promote progress through a patient’s phases of healing.

COMPARATIVE ANALGESIC EFFECTS OF SINGLE-DOSE PREOPERATIVE ADMINISTRATION OF PARACETAMOL (ACETAMINOPHEN) 500 mg PLUS CODEINE 30 mg AND IBUPROFEN 400 mg ON PAIN AFTER THIRD MOLAR SURGERY

BACKGROUND

Efficacy and rapid onset of postsurgical oral pain relief are critical to improve clinical outcomes and reduce the risk of excessive dosing with analgesic drugs.

PURPOSE

To compare analgesic effects of preoperative administration of paracetamol 500 mg plus codeine 30 mg in single-tablet and effervescent formulation to ibuprofen 400 mg, and placebo in the management of moderate to severe postoperative pain after mandibular third molar surgery.

MATERIALS AND METHODS

One hundred twenty healthy outpatients aged 15-29 years undergoing surgical removal of 1 bony impacted mandibular third molar were enrolled in this, single-center, prospective, randomized, triple-blind parallel-group, placebo-controlled, clinical trial. Study participants were randomly assigned to three treatment arms. According to the concealed allocation, each patient 30 minutes before surgery received paracetamol 500 mg plus codeine 30 mg (group APAP/COD), ibuprofen 400 mg (group IBU) or placebo (group PLA). Rescue therapy allowed in the postoperative period was paracetamol 500 mg plus codeine 30 mg in groups APAP/COD and PLA and ibuprofen 400 mg in group IBU. Patients recorded on Numerical Rating Scale-11 (NRS-11) the pain intensity, total number of postoperative-supplement medications and time of the first intake, until 12-hours after surgery and over extra 2 days, RESULTS: Over postoperative 3 days, patients in the APAP/COD group (2.33 ± 1.99) displayed significantly (P< .001) less pain intensity than IBU (3.43 ± 2.47) and placebo (3.57 ± 2.62) groups. The first-day postoperative pain was significantly (P < .001) higher in group PLA than in groups APAP/COD and IBU, but not between the latter 2 groups. However, at 2 hours postdose, the IBU group displayed average pain intensity lower than APAP/COD group (P> .05). On the next 2 days, pain intensity was significantly (P< .001) lower in group APAP/COD than in groups IBU and PLA but failed to reach statistical significance between groups IBU and PLA. Although the time to the first using rescue therapy was longer (445.88 ± 159.96 minute) in group IBU, compared to groups APAP/COD (392.67 ± 138.90 minutes) and PLA (323.00 ± 143.95 minutes), the number of supplemented tablets was significantly higher in group IBU (2.89 ± 2.13) than in groups APAP/COD (1.24 ± 1.79) (P= .001) and PLA (1.53 ± 1.67) (P = .008). No adverse events were registered for all groups.

CONCLUSIONS

Within the limits of the present study, over postoperative 3 days, a statistically significant intensity pain reduction and decreased rescue therapy consumption were recorded in the paracetamol-codeine group than to ibuprofen group. Nevertheless, lower pain intensity at 2 hours postdose and longer time using rescue therapy was found in the ibuprofen group without statistical significance. No adverse events occurred over the studied period.

Role of Primary Afferents in Arthritis Induced Spinal Microglial Reactivity

Increased afferent input resulting from painful injury augments the activity of central nociceptive circuits via both neuron-neuron and neuron-glia interactions. Microglia, resident immune cells of the central nervous system (CNS), play a crucial role in the pathogenesis of chronic pain. This study provides a framework for understanding how peripheral joint injury signals the CNS to engage spinal microglial responses. During the first week of monosodium iodoacetate (MIA)-induced knee joint injury in male rats, inflammatory and neuropathic pain were characterized by increased firing of peripheral joint afferents. This increased peripheral afferent activity was accompanied by increased Iba1 immunoreactivity within the spinal dorsal horn indicating microglial activation. Pharmacological silencing of C and A afferents with co-injections of QX-314 and bupivacaine, capsaicin, or flagellin prevented the development of mechanical allodynia and spinal microglial activity after MIA injection. Elevated levels of ATP in the cerebrospinal fluid (CSF) and increased expression of the ATP transporter vesicular nucleotide transporter (VNUT) in the ipsilateral spinal dorsal horn were also observed after MIA injections. Selective silencing of primary joint afferents subsequently inhibited ATP release into the CSF. Furthermore, increased spinal microglial reactivity, and alleviation of MIA-induced arthralgia with co-administration of QX-314 with bupivacaine were recapitulated in female rats. Our results demonstrate that early peripheral joint injury activates joint nociceptors, which triggers a central spinal microglial response. Elevation of ATP in the CSF, and spinal expression of VNUT suggest ATP signaling may modulate communication between sensory neurons and spinal microglia at 2 weeks of joint degeneration.

Effects of ibuprofen administration timing on oral surgery pain: A randomized clinical trial

OBJECTIVE

This study aimed to compare the analgesic effect of ibuprofen 400 mg given 30 min before or immediately after third molars surgery under local anaesthesia.

MATERIALS AND METHODS

The single-centre, randomized, split-mouth, triple-blind, clinical trial involved 38 outpatients, for a total of 76 bilateral symmetrical fully bone impacted mandibular third molars. Each patient was undergone to separate surgical sessions for the right and left side, and ibuprofen was randomly administered 30 min before or immediately after the intervention. Study participants recorded pain intensity using Numerical Rating Scale-11, the timing of rescue therapy intake and overall tablets consumption over 3 days.

RESULTS

The overall pain intensity score was lower in the group receiving ibuprofen immediately after (3.13 ± 2.46) than before (3.58 ± 2.40) surgery, with statistically significant differences only on the second and third days. The mean time to the first using rescue therapy was longer in the postoperative (598.33 ± 422.62 min) than in the preoperative (406.25 ± 149.79 min) analgesic treatment group (p = .123). The number of supplemented ibuprofen tablets did not differ (p = .530) between both groups.

CONCLUSIONS

Within the limits of the present study, ibuprofen administration immediately after surgery seemed to be more effective than preoperative administration.

Evidence-Based Strategies for the Prevention of Chronic Post-Intensive Care and Acute Care-Related Pain

Chronic pain is prevalent in intensive care survivors and in patients who require acute care treatments. Many adverse consequences have been associated with chronic post-intensive care and acute care-related pain. Hence, interest in interventions to prevent these pain disorders has grown. To improve the understanding of the mechanisms of action of these interventions and their potential impacts, this article outlines the pathophysiology involved in the transition from acute to chronic pain, the epidemiology and consequences of chronic post-intensive care and acute care- related pain, and risk factors for the development of chronic pain. Pharmacological, nonpharmacological, and multimodal preventive interventions specific to the targeted populations and their levels of evidence are presented. Nursing implications for preventing chronic pain in patients receiving critical and acute care are also discussed.

Contribution of Inflammation and Bone Destruction to Pain in Arthritis: A Study in Murine Glucose-6-Phosphate Isomerase-Induced Arthritis

OBJECTIVE

Arthritis is often characterized by inflammation and bone destruction. This study was undertaken to investigate the contribution of inflammation and bone destruction to pain.

METHODS

Inflammation, bone resorption, pain-related behaviors, and molecular markers (activating transcription factor 3 [ATF-3], p-CREB, and transient receptor potential vanilloid channel 1) in sensory neurons were measured in murine glucose-6-phosphate isomerase (G6PI)-induced arthritis, a model of rheumatoid arthritis. Depletion of Treg cells before immunization changed self-limiting arthritis into nonremitting arthritis with pronounced bone destruction. Zoledronic acid (ZA) was administered to reduce bone resorption.

RESULTS

Compared to nondepleted mice, Treg cell-depleted mice exhibited arthritis with more severe bone destruction and higher guarding scores (P < 0.05; n = 10 mice per group) as well as more persistent thermal hyperalgesia (P < 0.05), but displayed similar mechanical hyperalgesia at the hindpaws (n = 18-26 mice per group). These pain-related behaviors, as well as an up-regulation of the neuronal injury marker ATF-3 in sensory neurons (studied in 39 mice), appeared before the clinical score (inflammation) became positive and persisted in Treg cell-depleted and nondepleted mice. In the late stage of arthritis, Treg cell-depleted mice treated with ZA showed less bone resorption (<50%; P < 0.01) and less thermal hyperalgesia (P < 0.01) than Treg cell-depleted mice without ZA treatment (n = 15 mice per group), but ZA treatment did not reduce the clinical score and local mechanical hyperalgesia.

CONCLUSION

Pain-related behaviors precede and outlast self-limiting arthritis. In nonremitting arthritis with enhanced bone destruction, mainly local thermal, but not local mechanical, hyperalgesia was aggravated. The up-regulation of ATF-3 indicates an early and persisting affection of sensory neurons by G6PI-induced arthritis.

Quantitative sensory testing response patterns to capsaicin- and ultraviolet-B-induced local skin hypersensitization in healthy subjects: a machine-learned analysis

The comprehensive assessment of pain-related human phenotypes requires combinations of nociceptive measures that produce complex high-dimensional data, posing challenges to bioinformatic analysis. In this study, we assessed established experimental models of heat hyperalgesia of the skin, consisting of local ultraviolet-B (UV-B) irradiation or capsaicin application, in 82 healthy subjects using a variety of noxious stimuli. We extended the original heat stimulation by applying cold and mechanical stimuli and assessing the hypersensitization effects with a clinically established quantitative sensory testing (QST) battery (German Research Network on Neuropathic Pain). This study provided a 246 × 10-sized data matrix (82 subjects assessed at baseline, following UV-B application, and following capsaicin application) with respect to 10 QST parameters, which we analyzed using machine-learning techniques. We observed statistically significant effects of the hypersensitization treatments in 9 different QST parameters. Supervised machine-learned analysis implemented as random forests followed by ABC analysis pointed to heat pain thresholds as the most relevantly affected QST parameter. However, decision tree analysis indicated that UV-B additionally modulated sensitivity to cold. Unsupervised machine-learning techniques, implemented as emergent self-organizing maps, hinted at subgroups responding to topical application of capsaicin. The distinction among subgroups was based on sensitivity to pressure pain, which could be attributed to sex differences, with women being more sensitive than men. Thus, while UV-B and capsaicin share a major component of heat pain sensitization, they differ in their effects on QST parameter patterns in healthy subjects, suggesting a lack of redundancy between these models.

Double-blind placebo-controlled randomized clinical trial of ginger ( Zingiber officinale Rosc.) addition in migraine acute treatment

BACKGROUND

Previous studies have demonstrated the analgesic effects of ginger in different conditions, but evidence about its efficacy in migraine treatment is scarce.

OBJECTIVE

This study aimed to evaluate the potential of ginger to improve acute migraine as an add-on strategy to standard treatment.

METHODS

A double-blind placebo-controlled randomized clinical trial in the emergency room of a general hospital was conducted. Patients who sought medical care at the time of migraine attack were enrolled in this study. Only adults with episodic migraine (one to six migraine attacks per month) with or without aura were included. Sixty participants were randomized into two groups in which they received 400 mg of ginger extract (5% active ingredient) or placebo (cellulose), in addition to an intravenous drug (100 mg of ketoprofen) to treat the migraine attack. Patients filled a headache diary before, 0.5 h, 1 h, 1.5 h and 2 h after the medication. Pain severity, functional status, migraine symptoms and treatment satisfaction were also recorded.

RESULTS

Patients treated with ginger showed significantly better clinical response after 1 h ( p = 0.04), 1.5 h ( p = 0.01) and 2 h ( p = 0.04). Furthermore, ginger treatment promoted reduction in pain and improvement on functional status at all times assessed.

CONCLUSIONS

The addition of ginger to non-steroidal anti-inflammatory drugs may contribute to the treatment of migraine attack. This trial is registered at ClinicalTrials.gov (NCT02568644).

A Systematic Review: Mindfulness Intervention for Cancer-Related Pain

Moderate-to-severe pain is a common problem experienced by patients with cancer. Although analgesic drugs are effective, adverse side effects are common and some analgesic drugs are addictive. Nonpharmacological treatment may be a way to treat cancer pain without causing negative side effects. Mindfulness is used as an effective nonpharmacological treatment to improve quality of life (QoL) and to address psychological problems including distress, anxiety, stress, and depression. However, the effect of mindfulness on pain severity has not been sufficiently investigated. Therefore, a systematic review was undertaken to describe the effectiveness of mindfulness interventions for pain and its underlying pathophysiologic mechanisms. The search was conducted in PubMed, Ovid MEDLINE, and CINAHL and included only empirical studies published from 2008 to 2017. Search terms included mindfulness, mindfulness-based intervention, meditation, cancer, pain, and cancer-related pain. Six studies met the search criteria. These studies tested several types of intervention including mindfulness-based stress reduction, mindfulness-based cognitive therapy, meditation with massage, and mindful awareness practices. Study outcomes include improved pain severity, anxiety, stress, depression, and QoL. However, most studies reviewed were conducted in the United States and Denmark. Further research is needed to test culturally appropriate mindfulness interventions to reduce pain.

The impact of opioid analgesic prescription uptake on the costs of recovery from injury: Evidence from compensable orthopaedic road trauma patients

Long-term opioid prescribing after compensable orthopaedic injury may contribute to the 'long right tail' in the cost of recovery. The aim of this study was to estimate the effect of prescription opioid uptake on injury compensation cost, using orthopaedic road traffic injury claims data from Victoria, Australia. We used a maximum likelihood estimation that accounts for potential endogeneity associated with opioid uptake, utilizing information on the doctor's differential propensity to prescribe opioids when treating other compensable injury patients. Our results suggest that opioid recipients incurred significantly greater hospital costs, income compensation payments, and medical and paramedical expenses. Overall, income compensation was the primary driver of the claim cost difference between opioid recipients and non-recipients. The findings imply that there is scope to impose restrictions on long-term opioid usage, and to encourage the use of alternative pain relief medicines.

Patients with type 2 diabetes demonstrate proprioceptive deficit in the knee

AIM

To investigate proprioceptive discrepancies in the lower extremity in persons with type 2 diabetes mellitus (T2DM).

METHODS

In this cross-sectional study, a total of 46 older persons were divided into a T2DM group (n = 23) and a control group who did not have T2DM (n = 23). Participants were given a brief warm up with stretching exercises. Diabetic neuropathy scores were collected prior to proprioceptive testing. For proprioceptive testing, participants performed leg extensions to randomized target positions of 15°, 30°, 45, 60° degrees of elevation in the sagittal plane, each target was repeated a total of four times. Subjects were guided to target positions in the absence of visual feedback via auditory cues from a custom JPS application. When the participant entered the target position, they memorized the location of their limb in space and subsequently attempted to re-locate this position in space. Proprioceptive errors were measured from the target positioned, target remembered, target repositioned protocol.

RESULTS

Proprioceptive accuracy was lower in the diabetic group at all levels of target angle than the control group (P < 0.05). The diabetic group had 46% greater inaccuracy than the control group at all levels of target position. Diabetics also reported greater neuropathy scores than controls in the past 12 mo P < 0.01.

CONCLUSION

Deficits in lower limb localization and greater diabetic neuropathy scores were identified in this study. Our findings may be associated with deafferentation as peripheral neuropathy is a common complication with the disease. These findings may help to explain the declining balance function in the older persons with T2DM which is also commonly reported.

Mechanisms of Osteoarthritic Pain. Studies in Humans and Experimental Models

Pain due to osteoarthritis (OA) is one of the most frequent causes of chronic pain. However, the mechanisms of OA pain are poorly understood. This review addresses the mechanisms which are thought to be involved in OA pain, derived from studies on pain mechanisms in humans and in experimental models of OA. Three areas will be considered, namely local processes in the joint associated with OA pain, neuronal mechanisms involved in OA pain, and general factors which influence OA pain. Except the cartilage all structures of the joints are innervated by nociceptors. Although the hallmark of OA is the degradation of the cartilage, OA joints show multiple structural alterations of cartilage, bone and synovial tissue. In particular synovitis and bone marrow lesions have been proposed to determine OA pain whereas the contribution of the other pathologies to pain generation has been studied less. Concerning the peripheral neuronal mechanisms of OA pain, peripheral nociceptive sensitization was shown, and neuropathic mechanisms may be involved at some stages. Structural changes of joint innervation such as local loss and/or sprouting of nerve fibers were shown. In addition, central sensitization, reduction of descending inhibition, descending excitation and cortical atrophies were observed in OA. The combination of different neuronal mechanisms may define the particular pain phenotype in an OA patient. Among mediators involved in OA pain, nerve growth factor (NGF) is in the focus because antibodies against NGF significantly reduce OA pain. Several studies show that neutralization of interleukin-1β and TNF may reduce OA pain. Many patients with OA exhibit comorbidities such as obesity, low grade systemic inflammation and diabetes mellitus. These comorbidities can significantly influence the course of OA, and pain research just began to study the significance of such factors in pain generation. In addition, psychologic and socioeconomic factors may aggravate OA pain, and in some cases genetic factors influencing OA pain were found. Considering the local factors in the joint, the neuronal processes and the comorbidities, a better definition of OA pain phenotypes may become possible. Studies are under way in order to improve OA and OA pain monitoring.

Analgesic Effects of Locally Administered Ketorolac-based Analgesics After Breast Surgery: A Meta-Analysis of Randomized Controlled Trials

OBJECTIVE

Reducing postoperative pain following breast surgery is crucial for rapid recovery and shortening hospital stay. Ketorolac, a nonsteroidal anti-inflammatory drug, has been used as a postoperative analgesic in many surgical procedures. We conducted a systemic review and meta-analysis on the efficacy of locally administered ketorolac-based analgesics in managing pain after breast surgery.

METHODS

We searched the PubMed, Embase, Cochrane Library, Scopus, and ClinicalTrials.gov registry for randomized control trials (RCTs) published up to September 2016. The primary outcome was pain level assessed using a visual analog scale (VAS) at 1 and 6 hours following breast surgery.

RESULTS

We reviewed 4 RCTs with 255 patients. For meta-analysis, VAS at 1 and 6 hours of 3 similar RCTs were compared. At 1 hour, VAS scores were significantly lower in patients administered a ketorolac solution [weighted mean difference (WMD)=-2.04; 95% confidence interval (CI): -3.08 to -1.00] or ketorolac-bupivacaine solution (WMD=-2.30; 95% CI, -4.07 to -0.54) than in controls. At 6 hours, the ketorolac-bupivacaine solution reduced VAS scores significantly (WMD=-1.40; 95% CI, -2.48 to -0.32) compared with controls. However, at 1 hour, the ketorolac solution was significantly more effective than the bupivacaine solution was (WMD=-1.70; 95% CI, -2.81 to -0.59).

DISCUSSION

The effects of ketorolac-based analgesics vary as per the surgery and disease type. Locally administered ketorolac-based analgesics decreased postoperative pain in breast surgery patients, and the effect of local ketorolac was better than local bupivacaine. Therefore, ketorolac-based analgesics demonstrate considerable local infiltration during pain management after breast surgery.

The interfaces between vitamin D, sleep and pain

The role of vitamin D in osteomineral metabolism is well known. Several studies have suggested its action on different biological mechanisms, such as nociceptive sensitivity and sleep-wake cycle modulation. Sleep is an important biological process regulated by different regions of the central nervous system, mainly the hypothalamus, in combination with several neurotransmitters. Pain, which can be classified as nociceptive, neuropathic and psychological, is regulated by both the central and peripheral nervous systems. In the peripheral nervous system, the immune system participates in the inflammatory process that contributes to hyperalgesia. Sleep deprivation is an important condition related to hyperalgesia, and recently it has also been associated with vitamin D. Poor sleep efficiency and sleep disorders have been shown to have an important role in hyperalgesia, and be associated with different vitamin D values. Vitamin D has been inversely correlated with painful manifestations, such as fibromyalgia and rheumatic diseases. Studies have demonstrated a possible action of vitamin D in the regulatory mechanisms of both sleep and pain. The supplementation of vitamin D associated with good sleep hygiene may have a therapeutic role, not only in sleep disorders but also in the prevention and treatment of chronic pain conditions.

A small yet comprehensive subset of human experimental pain models emerging from correlation analysis with a clinical quantitative sensory testing protocol in healthy subjects

BACKGROUND

Picturing the complexity of pain in human experimental settings has increased the predictivity for clinical pain but requires increasingly complex test batteries. This raises problems in studies in which time is objectively limited, for example by the course of action of an analgesic drug. We addressed the selection of a small yet comprehensive set of pain tests for the use in such a situation.

METHOD

Nineteen different pain measures from 'classical' pain models (n = 9) and a clinically established QST-pain test battery (n = 10), were obtained from 72 healthy volunteers (34 men). The nonparametric correlation structure among the various pain measures was analysed using Ward clustering.

RESULTS

Four clusters emerged, each consisting of highly correlated pain measures. The pain model groups emerged comprised (I) pain thresholds and tolerances to blunt pressure or electrical pain; (II) pain thresholds to thermal stimuli; (III) pain measures obtained following application of punctate mechanical, intranasal CO2 chemical or cutaneous laser heat stimuli; and (IV) detection thresholds to thermal stimuli. The first three clusters agreed with an immediate mechanistic interpretation as reflecting C-fibre mediated pain, thermal pain and Aδ-fibre mediated pain, respectively, whereas the last cluster contained non-painful measures and was disregarded.

CONCLUSIONS

When basing a selection of a small comprehensive set of pain models on the assumption that highly correlated pain measures account for redundant results and therefore, one member of each group suffices an economic yet comprehensive pain study, results suggest inclusion of established C-fibre, Aδ-fibre mediated and thermal pain measures.

Nociception and role of immune system in pain

Both pain and inflammation are protective responses. However, these self-limiting conditions (with well-established negative feedback loops) become pathological if left uncontrolled. Both pain and inflammation can interact with each other in a multi-dimensional manner. These interactions are known to create an array of 'difficult to manage' pathologies. This review explains in detail the role of immune system and the related cells in peripheral sensitization and neurogenic inflammation. Various neuro-immune interactions are analyzed at peripheral, sensory and central nervous system levels. Innate immunity plays a critical role in central sensitization and in establishing acute pain as chronic condition. Moreover, inflammatory mediators also exhibit psychological effects, thus contributing towards the emotional elements associated with pain. However, there is also a considerable anti-inflammatory and analgesic role of immune system. This review also attempts to enlist various novel pharmacological approaches that exhibit their actions through modification of neuro-immune interface.

Expression of Prostaglandin E2 Enzymes in the Synovium of Arthralgia Patients at Risk of Developing Rheumatoid Arthritis and in Early Arthritis Patients

Objective

Arthralgia may precede the development of synovial inflammation in autoantibody-positive individuals at risk of developing rheumatoid arthritis (RA). A major pathway involved in pain is the prostaglandin (PG) E₂ pathway. We investigated this pathway in the synovium of individuals with RA-specific autoantibodies and in early arthritis patients.

Methods

Nineteen autoantibody-positive individuals (IgM-rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies) with arthralgia (n=15) and/or a positive family history of RA (n=8), who had been prospectively followed for at least 2 years, were included. In addition, we included early arthritis patients (disease-modifying antirheumatic drug naïve) who after 2 years follow up fulfilled classification criteria for RA (n=63), spondyloarthritis (SpA; n=14), or had unclassified arthritis (UA; n=27). In all subjects we assessed pain and performed synovial biopsy sampling by mini-arthroscopy at baseline. Tissue sections were examined by immunohistochemistry to detect and quantify PGE₂ pathway enzymes expression levels (mPGES-1; COX-1 and -2; 15-PGDH).

Results

In both study groups synovial expression of PGE₂ enzymes was not clearly related to pain sensation. Expression levels at baseline were not associated with the development of arthritis after follow up (6 out of 19 autoantibody-positive individuals). However, in early SpA patients the expression levels of mPGES-1 and COX-1 were significantly increased compared to RA and UA patients.

Conclusion

Pain in autoantibody-positive individuals without synovial inflammation who are at risk of developing RA and in early arthritis patients may be regulated by pathways other than the PGE₂ pathway or originate at sites other than the synovium. In contrast, in SpA, the PGE2 pathway may be inherently linked to the pathophysiology/etiology of the disease.

Nociception at the diabetic foot, an uncharted territory

The diabetic foot is characterised by painless foot ulceration and/or arthropathy; it is a typical complication of painless diabetic neuropathy. Neuropathy depletes the foot skin of intraepidermal nerve fibre endings of the afferent A-delta and C-fibres, which are mostly nociceptors and excitable by noxious stimuli only. However, some of them are cold or warm receptors whose functions in diabetic neuropathy have frequently been reported. Hence, it is well established by quantitative sensory testing that thermal detection thresholds at the foot skin increase during the course of painless diabetic neuropathy. Pain perception (nociception), by contrast, has rarely been studied. Recent pilot studies of pinprick pain at plantar digital skinfolds showed that the perception threshold was always above the upper limit of measurement of 512 mN (equivalent to 51.2 g) at the diabetic foot. However, deep pressure pain perception threshold at musculus abductor hallucis was beyond 1400 kPa (equivalent to 14 kg; limit of measurement) only in every fifth case. These discrepancies of pain perception between forefoot and hindfoot, and between skin and muscle, demand further study. Measuring nociception at the feet in diabetes opens promising clinical perspectives. A critical nociception threshold may be quantified (probably corresponding to a critical number of intraepidermal nerve fibre endings), beyond which the individual risk of a diabetic foot rises appreciably. Staging of diabetic neuropathy according to nociception thresholds at the feet is highly desirable as guidance to an individualised injury prevention strategy.

Emerging concepts of pain therapy based on neuronal mechanisms

Current pain treatment is successful in many patients, but nevertheless numerous problems have to be solved because still about 20% of the people in the population suffer from chronic pain. A major aim of pain research is, therefore, to clarify the neuronal mechanisms which are involved in the generation and maintenance of different pain states and to identify the mechanisms which can be targeted for pain treatment. This volume on pain control addresses neuronal pain mechanisms at the peripheral, spinal, and supraspinal level which are thought to significantly contribute to pain and which may be the basis for the development of new treatment principles. This introductory chapter addresses the types of pain which are currently defined based on the etiopathologic considerations, namely physiologic nociceptive pain, pathophysiologic nociceptive pain, and neuropathic pain. It briefly describes the structures and neurons of the nociceptive system, and it addresses molecular mechanisms of nociception which may become targets for pharmaceutical intervention. It will provide a frame for the chapters which address a number of important topics. Such topics are the concept of hyperalgesic priming, the role of voltage-gated sodium channels and nerve growth factor (NGF) in different inflammatory and neuropathic pain states, the hyperalgesic effects of NGF in different tissues, the contribution of proteinase-activated receptors (PARs) to the development of pain in several chronic pain conditions, the role of spinal NO and of glial cell activation in the generation and maintenance of inflammatory and neuropathic pain, the potential role of spinal inhibitory interneurons, the endogenous endocannabinoid system, and the importance of nonneuronal immune mechanisms in opioid signaling in the control of pain, the influence of spinal mechanisms on the expression of peripheral inflammation, the role of the amygdala and their connections to the medial prefrontal cortex in pain states, the experimental methods to test central sensitization of the nociceptive system in humans, and differences and similarities of the neuronal systems of pain and itch. Finally it will be discussed that both the concentration on single key molecules of nociception and the interference with disease-related mediators may provide novel approaches of pain treatment.

Effect of painless diabetic neuropathy on pressure pain hypersensitivity (hyperalgesia) after acute foot trauma

Introduction and objective

Acute injury transiently lowers local mechanical pain thresholds at a limb. To elucidate the impact of painless (diabetic) neuropathy on this post-traumatic hyperalgesia, pressure pain perception thresholds after a skeletal foot trauma were studied in consecutive persons without and with neuropathy (i.e. history of foot ulcer or Charcot arthropathy).

Design and methods

A case–control study was done on 25 unselected clinical routine patients with acute unilateral foot trauma (cases: elective bone surgery; controls: sprain, toe fracture). Cases were 12 patients (11 diabetic subjects) with severe painless neuropathy and chronic foot pathology. Controls were 13 non-neuropathic persons. Over 1 week after the trauma, cutaneous pressure pain perception threshold (CPPPT) and deep pressure pain perception threshold (DPPPT) were measured repeatedly, adjacent to the injury and at the opposite foot (pinprick stimulators, Algometer II^®).

Results

In the control group, post-traumatic DPPPT (but not CPPPT) at the injured foot was reduced by about 15–25%. In the case group, pre- and post-operative CPPPT and DPPPT were supranormal. Although DPPPT fell post-operatively by about 15–20%, it remained always higher than the post-traumatic DPPPT in the control group: over musculus abductor hallucis 615 kPa (kilopascal) versus 422 kPa, and over metatarsophalangeal joint 518 kPa versus 375 kPa (medians; case vs. control group); CPPPT did not decrease post-operatively.

Conclusion

Physiological nociception and post-traumatic hyperalgesia to pressure are diminished at the foot with severe painless (diabetic) neuropathy. A degree of post-traumatic hypersensitivity required to ‘pull away’ from any one, even innocuous, mechanical impact in order to avoid additional damage is, therefore, lacking.

Hemopressin, an inverse agonist of cannabinoid receptors, inhibits neuropathic pain in rats

Direct-acting cannabinoid receptor ligands are well known to reduce hyperalgesic responses after nerve injury, although their psychoactive side effects have damped enthusiasm for their therapeutic development. Hemopressin (Hp) is a nonapeptide that selectively binds CB1 cannabinoid receptors (CB1 receptors) and exerts antinociceptive action in inflammatory pain models. We investigated the effect of Hp on neuropathic pain in rats subjected to chronic constriction injury (CCI) of the sciatic nerve, and explored the mechanisms involved. Oral administration of Hp inhibits mechanical hyperalgesia of CCI-rats up to 6h. Hp treatment also decreases Egr-1 immunoreactivity (Egr-1Ir) in the superficial layer of the dorsal horn of the spinal cord of CCI rats. The antinociceptive effect of Hp seems to be independent of inhibitory descending pain pathway since methysergide (5HT1A receptor antagonist) and yohimbine (α-2 adrenergic receptor antagonist) were unable to prevent Hp antinociceptive effect. Hp decreased calcium flux on DRG neurons from CCI rats, similarly to that observed for AM251, a CB1 receptor antagonist. We also investigated the effect of Hp on potassium channels of CCI rats using UCL 1684 (a blocker of Ca(2+)-activated K(+) channels) which reversed Hp-induced antinociception. Furthermore, concomitant administration of URB-584 (FAAH inhibitor) but not JZL-184 (MAGL inhibitor) potentiates antinociceptive effect of Hp in CCI rats indicating an involvement of anadamide on HP-induced antinociception. Together, these data demonstrate that Hp displays antinociception in pain from neuropathic etiology through local effects. The release of anandamide and the opening of peripheral K(+) channels are involved in the antinociceptive effect.

Intra-Articular Analgesia and Steroid Reduce Pain Sensitivity in Knee OA Patients: An Interventional Cohort Study

Objectives. To assess the effects of intra-articular therapy on pain sensitivity in the knee and surrounding tissues in knee OA patients. Methods. Twenty-five knee OA patients with symptomatic knee OA were included in this interventional cohort study. Pressure pain thresholds (PPT) were recorded before, immediately after, and two weeks after ultrasound guided intra-articular injection of lidocaine combined with glucocorticosteroid. Computer-controlled and manual pressure algometers were used to assess PPT on the knee, vastus lateralis, tibialis anterior, and the extensor carpi radialis longus muscles (control site). Results. Significantly increased PPTs were found following intra-articular injection, at both the knee (P < 0.0001) and the surrounding muscles (P < 0.042). The treatment effects were sustained for two weeks, and at some points the effect was even greater at two weeks (P < 0.026). Albeit not statistically significant, a similar trend was observed at the control site. Conclusions. Intra-articular anesthesia, combined with glucocorticosteroid, reduced pain sensitivity in both the knee and surrounding muscles for at least two weeks.

Novel anti-nociceptive effects of cardamonin via blocking expression of cyclooxygenase-2 and transglutaminase-2

Recently, we reported that Alpinia katsumadai (AK) has anti-nociceptive activity in vivo and that cardamonin (CDN) from AK suppresses the activity and expression of transglutaminase-2 (Tgase-2). However, it remains unknown whether CDN contributes to the anti-nociceptive activities of AK in vivo. We examined the anti-inflammatory effects of CDN in MG63 osteoblast-like cells and Raw264.7 macrophage-like cells treated with interleukin-1β treatment. CDN suppressed the expression of Tgase-2, cyclooxygenase-2 (COX-2), and p65 (nuclear factor-κB) in a concentration-dependent manner, and restored the expression of IκB in MG63 and Raw264.7 cells. However, CDN did not inhibit the activity of COX-2. Gene silencing of Tgase-2 reduced the COX-2 expression in MG63 cells. Phenylbenzoquinone (PBQ)-induced writhing, carrageenan-induced hyperalgesia, and rota-rod test were used to evaluate the anti-nociceptive activity in vivo. CDN (3-30 mg/kg, orally administered) significantly inhibited PBQ-induced writhing. CDN also produced a significant, dose-dependent increase in the withdrawal response latencies in carrageenan-induced hyperalgesia. The effects of CDN on PBQ-induced writhing were not caused by impaired motor functions. These results suggest that CDN might be helpful in controlling the pain from inflammatory diseases.

Common biological pathways underlying the psychoneurological symptom cluster in cancer patients

BACKGROUND

A symptom cluster is a group of symptoms that occur together and are interrelated. The clinical implication of symptom cluster research is to use the clustering patterns of symptoms to understand the mechanisms for these symptoms and develop management strategies targeted at multiple symptoms.

OBJECTIVE

The purposes of this review were to summarize the evidence for a psychoneurological symptom cluster in cancer patients, to provide information regarding the underlying biological mechanisms for each of the psychoneurological symptoms within the cluster, and to propose possible common biological pathways that may underlie this cluster.

METHODS

A systematic review of the literature was conducted.

RESULTS

Empirical evidence exists to support a cluster of psychoneurological symptoms (ie, depressive symptoms, cognitive disturbance, fatigue, sleep disturbance, pain). At a molecular level, common biological pathways (ie, proinflammatory cytokines, hypothalamic-pituitary-adrenal axis, and monoamine neurotransmission system) may underlie the development of symptoms within this cluster. Activation of proinflammatory cytokines is proposed as a first stage of mechanistic pathway. However, other biological factors, such as lowered estrogen or hemoglobin levels, may influence psychoneurological cluster.

CONCLUSION

Additional studies are needed to confirm the roles of cytokines as well as other biological factors in the development of the psychoneurological cluster and to determine the biomarkers to identify the subgroups of cancer patients who are at greatest risk for this cluster.

IMPLICATIONS FOR PRACTICE

This information can be used by researchers and clinicians to guide the selection of symptom management strategies that are ideally targeted to the biological mechanisms that underlie this symptom cluster.

AGH is a new hemoglobin alpha-chain fragment with antinociceptive activity

Limited proteolysis of certain proteins leads to the release of endogenous bioactive peptides. Hemoglobin-derived peptides such as hemorphins and hemopressins are examples of intracellular protein-derived peptides that have antinociceptive effects by modulating G-protein coupled receptors activities. In the present study, a previously characterized substrate capture assay that uses a catalytically inactive form of the thimet oligopeptidase was combined with isotopic labeling and mass spectrometry in order to identify new bioactive peptides. Indeed, we have identified the peptide AGHLDDLPGALSAL (AGH), a fragment of the hemoglobin alpha-chain, which specifically bind to the inactive thimet oligopeptidase in the substrate capture assay. Previous peptidomics studies have identified the AGH as well as many other natural peptides derived from hemoglobin alpha-chain containing this sequence, further suggesting that AGH is a natural endogenous peptide. Pharmacological assays suggest that AGH inhibits peripheral inflammatory hyperalgesic responses through indirect activation of mu opioid receptors, without having a central nervous system activity. Therefore, we have successfully used the substrate capture assay to identify a new endogenous bioactive peptide derived from hemoglobin alpha-chain.

Antinociceptive and anti-inflammatory potential of extract and isolated compounds from the leaves of Salvia officinalis in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia officinalis L. has been used as a traditional herbal medicine for gastric disturbances and inflammatory processes. This study investigated the toxicological, antinociceptive and anti-inflammatory effects of the hydroalcoholic extract (HE) from leaves of Salvia officinalis and its isolated compounds in mice.

MATERIALS AND METHODS

Mice were treated with HE before the induction of nociceptive response by chemical agents (acetic-acid, formalin, glutamate, capsaicin and cinnamaldehyde). Total leukocytes and plasma extravasation induced by acetic acid and paw oedema induced by glutamate, capsaicin and cinnamaldehyde were also measured. The antinociceptive effect of carnosol and ursolic acid/oleanolic acid were evaluated on formalin and cinnamaldehyde models.

RESULTS

In the acute toxicity test the value of estimated LD50 for HE was 44.7579 g/kg. Oral administration of HE (10, 30 and 100 mg/kg) inhibited the number of writhings, total leukocytes and plasma extravasation induced by acetic acid. In the formalin test, HE reduced both neurogenic and inflammatory phases, effect that was affected by naloxone. The glutamate-, capsaicin- and cinnamaldehyde-induced nociception and paw oedema were reduced by HE at doses that did not affect the locomotor activity of mice in the open field test. Carnosol (10mg/kg) and ursolic acid/oleanolic acid (30 mg/kg) inhibited the inflammatory phase of formalin and the nociception and mechanical allodynia induced by cinnamaldehyde.

CONCLUSIONS

These results demonstrate that HE presents significant anti-inflammatory and also antinociceptive effects on chemical behavioral models of nociception that involves an opioid mechanism. In addition, carnosol and ursolic acid/oleanolic acid contained in this plant appears to contribute for the antinociceptive property of the extract, possibly through a modulatory influence on TRPA1-receptors. However, further studies regarding the precise site and the mechanism of action of HE and carnosol and ursolic acid/oleanolic acid merited exploring further.

Update on peripheral mechanisms of pain: beyond prostaglandins and cytokines

The peripheral nociceptor is an important target of pain therapy because many pathological conditions such as inflammation excite and sensitize peripheral nociceptors. Numerous ion channels and receptors for inflammatory mediators were identified in nociceptors that are involved in neuronal excitation and sensitization, and new targets, beyond prostaglandins and cytokines, emerged for pain therapy. This review addresses mechanisms of nociception and focuses on molecules that are currently favored as new targets in drug development or that are already targeted by new compounds at the stage of clinical trials--namely the transient receptor potential V1 receptor, nerve growth factor, and voltage-gated sodium channels--or both.

NMDA receptor antagonists for the treatment of neuropathic pain

OBJECTIVE

The N-methyl-D-Aspartate (NMDA) receptor has been proposed as a primary target for the treatment of neuropathic pain. The aim of the present study was to perform a meta-analysis evaluating the effects of (individual) NMDA receptor antagonists on neuropathic pain, and the response (sensitivity) of individual neuropathic pain disorders to NMDA receptor antagonist therapy.

DESIGN

PubMed (including MEDLINE), EMBASE and CENTRAL were searched up to October 26, 2009 for randomized placebo controlled trials (RCTs) on neuropathic pain. The methodological quality of the included trials was independently assessed by two authors using the Delphi list. Fixed or random effects model were used to calculate the summary effect size using Hedges' g.

SETTING

NA.

PATIENTS

The patients used for the study were neuropathic pain patients.

INTERVENTIONS

The interventions used were NMDA receptor antagonists.

OUTCOME MEASUREMENTS

The outcome of measurements was the reduction of spontaneous pain.

RESULTS

Twenty-eight studies were included, meeting the inclusion criteria. Summary effect sizes were calculated for subgroups of studies evaluating ketamine IV in complex regional pain syndrome (CRPS), oral memantine in postherptic neuralgia and, respectively, ketamine IV, and oral memantine in postamputation pain. Treatment with ketamine significantly reduced pain in postamputation pain (pooled summary effect size: -1.18 [confidence interval (CI) 95% -1.98, -0.37], P = 0.004). No significant effect on pain reduction could be established for ketamine IV in CRPS (-0.65 [CI 95% -1.47, 0.16], P = 0.11) oral memantine in postherptic neuralgia (0.03 [CI 95% -0.51, 0.56], P = 0.92) and for oral memantine in postamputation pain (0.38 [CI 95% -0.21, 0.98], P = 0.21).

CONCLUSIONS

Based on this systematic review, no conclusions can yet be made about the efficacy of NMDA receptor antagonists on neuropathic pain. Additional RCTs in homogenous groups of pain patients are needed to explore the therapeutic potential of NMDA receptor antagonists in neuropathic pain.

Gait analysis and pain response of two rodent models of osteoarthritis

The purpose of this study was to compare the gait parameters recorded on the CatWalk and the mechanical sensitivity with von Frey filaments of two putative models of osteoarthritis over a one month period, and to evaluate the effect of celecoxib on these parameters. Animals underwent either a surgical sectioning of the anterior cruciate ligament with partial medial menisectomy (ACLT+pMMx) to create a joint instability model or received an intra-articular injection of monoiodoacetate (MIA) as a putative inflammatory joint pain model. Animals were assessed for four consecutive weeks and knee joints were then evaluated histologically. Spinal cord lumbar enlargements were harvested for selected neuropeptide analysis (substance P (SP) and calcitonin gene related peptide (CGRP)). With the MIA model, significant changes persisted in selected dynamic gait parameters throughout the study in the injured limb as well as with the von Frey filaments. The ACLT+pMMx model in contrast showed no clear differential response between both hind limb for both gait parameters and pain-related behavior with von Frey filaments occurred only on the last day of the study. Neuropeptide analysis of spinal cord lumbar enlargements revealed a significant increase in CGRP concentration in both models and an increase in SP concentration only in the MIA model. Histological evaluation confirmed the presence of articular cartilage lesions in both models, but they were much more severe in the MIA model. Celecoxib had an effect on all selected gait parameters at the very beginning of the study and had an important alleviating effect on mechanical allodynia. These results suggest that the MIA model may be more appropriate for the evaluation of short term pain studies and that celecoxib may modulate mechanical allodynia through central sensitization mechanisms.

Physiology and pharmacology of the vanilloid receptor

The identification and cloning of the vanilloid receptor 1 (TRPV1) represented a significant step for the understanding of the molecular mechanisms underlying the transduction of noxious chemical and thermal stimuli by peripheral nociceptors. TRPV1 is a non-selective cation channel gated by noxious heat, vanilloids and extracellular protons. TRPV1 channel activity is remarkably potentiated by pro-inflammatory agents, a phenomenon that is thought to underlie the peripheral sensitisation of nociceptors that leads to thermal hyperalgesia. Cumulative evidence is building a strong case for the involvement of this receptor in the etiology of both peripheral and visceral inflammatory pain, such as inflammatory bowel disease, bladder inflammation and cancer pain. The validation of TRPV1 receptor as a key therapeutic target for pain management has thrust intensive drug discovery programs aimed at developing orally active antagonists of the receptor protein. Nonetheless, the real challenge of these drug discovery platforms is to develop antagonists that preserve the physiological activity of TRPV1 receptors while correcting over-active channels. This is a condition to ensure normal pro-prioceptive and nociceptive responses that represent a safety mechanism to prevent tissue injury. Recent and exciting advances in the function, dysfunction and modulation of this receptor will be the focus of this review.

Arthrogenic lameness of the fetlock: synovial fluid markers of inflammation and cartilage turnover in relation to clinical joint pain

REASONS FOR PERFORMING THE STUDY

Joint pain is one of the most common causes of lameness in the horse but its pathogenesis is poorly understood.

OBJECTIVES

To investigate which synovial fluid markers may be related to the presence of clinically detectable joint pain in the horse.

METHODS

Concentrations of structural (CPII, C2C, GAG) and inflammatory markers (PGE2, LTB4, CysLTs, bradykinin and substance P) were measured in fetlock joint fluid from 22 horses in which lameness was localised to the fetlock region by perineural anaesthesia. Levels of these markers were then compared in horses that responded (n = 15) to those that did not (n = 7) to subsequent intra-articular anaesthesia (IAA).

RESULTS

Of all markers analysed, only substance P levels were significantly higher (P = 0.0358) in synovial fluid of horses that showed a positive response to IAA compared to those with a negative response to IAA. Notably, while PGE2 levels were found to be elevated in all 22 lame horses compared to sound controls (P = 0.0025), they were not related to the response to IAA.

CONCLUSIONS

While levels of PGE2 are elevated in synovial fluid of lame horses that respond to perineural anaesthesia, only substance P is related to joint pain as detected by the response to intra-articular anaesthesia.

POTENTIAL RELEVANCE

Substance P is associated with clinically detectable joint pain in the horse. Elevated levels of PGE2 in fetlock-lame horses, regardless of their response to IAA, indicate that either this mediator does not reflect intra-articular pain or that IAA might have limitations in differentiating between intra- and peri-articular sources of pain. Either way, a negative response to IAA may not exclude intra-articular pathology.