Widespread Mechanical Pain Hypersensitivity as Sign of Central Sensitization in Unilateral Epicondylalgia: A Blinded, Controlled Study

Clinical presentation and manual therapy for upper quadrant musculoskeletal conditions

In recent years, increased knowledge of the pathogenesis of upper quadrant pain syndromes has translated to better management strategies. Recent studies have demonstrated evidence of peripheral and central sensitization mechanisms in different local pain syndromes of the upper quadrant such as idiopathic neck pain, lateral epicondylalgia, whiplash-associated disorders, shoulder impingement, and carpal tunnel syndrome. Therefore, a treatment-based classification approach where subjects receive matched interventions has been developed and, it has been found that these patients experience better outcomes than those receiving non-matched interventions. There is evidence suggesting that the cervical and thoracic spine is involved in upper quadrant pain. Spinal manipulation has been found to be effective for patients with elbow pain, neck pain, or cervicobrachial pain. Additionally, it is known that spinal manipulative therapy exerts neurophysiological effects that can activate pain modulation mechanisms. This paper exposes some manual therapies for upper quadrant pain syndromes, based on a nociceptive pain rationale for modulating central nervous system including trigger point therapy, dry needling, mobilization or manipulation, and cognitive pain approaches.

Translational musculoskeletal pain research

Diagnosis and management of musculoskeletal pain is a major clinical challenge. Fundamental knowledge of nociception from deep somatic structures and related mechanisms of sensitisation have been characterised in animals but the translation into clinical sciences is still lacking. Development and refinement of mechanism-based quantitative sensory testing in healthy volunteers and pain patients have provided new opportunities to assess pain and hyperalgesic reactions. The current technologies can provide information about, for example, peripheral and central sensitisation, descending pain control, central integration and structure specific sensitisation. Such a mechanistic approach can be used for differentiated diagnosis and for target validating new and existing analgesics. Mechanistic pain assessment of new compounds under development provides opportunities for target validation in proof-of-concept studies, which generate information to be used for selecting the most optimal patients for later clinical trials. New safe and efficient compounds are highly needed in the area of musculoskeletal pain management.

Increased pain sensitivity is not associated with electrodiagnostic findings in women with carpal tunnel syndrome

OBJECTIVE

To determine the differences in widespread pressure pain and thermal hypersensitivity in women with minimal, moderate, and severe carpal tunnel syndrome (CTS) and healthy controls.

METHODS

A total of 72 women with CTS (19 with minimal, 18 with moderate, and 35 with severe) and 19 healthy age-matched women participated. Pressure pain thresholds were bilaterally assessed over the median, ulnar, and radial nerves, the C5 to C6 zygapophyseal joint, the carpal tunnel, and the tibialis anterior muscle. In addition, warm and cold detection thresholds and heat and cold pain thresholds were bilaterally assessed over the carpal tunnel and the thenar eminence. All outcome parameters were assessed by an assessor blinded to the participant's condition.

RESULTS

No significant differences in pain parameters among patients with minimal, moderate, and severe CTS were found. The results showed that PPT were significantly decreased bilaterally over the median, ulnar, and radial nerve trunks, the carpal tunnel, C5 to C6 zygapophyseal joint, and the tibialis anterior muscle in patients with minimal, moderate, or severe CTS as compared with healthy controls (all, P<0.001). In addition, patients with CTS also showed lower heat pain threshold and reduced cold pain threshold compared with controls (P<0.001). No significant sensory differences between minimal, moderate, or severe CTS were found.

CONCLUSIONS

The similar widespread pressure and thermal hypersensitivity in patients with minimal, moderate, or severe CTS and pain intensity suggests that increased pain sensitivity is not related to electrodiagnostic findings.

Changes in pain sensitivity following spinal manipulation: a systematic review and meta-analysis

Spinal manipulation (SMT) is commonly used for treating individuals experiencing musculoskeletal pain. The mechanisms of SMT remain unclear; however, pain sensitivity testing may provide insight into these mechanisms. The purpose of this systematic review is to examine the literature on the hypoalgesic effects of SMT on pain sensitivity measures and to quantify these effects using meta-analysis. We performed a systematic search of articles using CINAHL, MEDLINE, PsycINFO, and SPORTDiscus from each databases' inception until May 2011. We examined methodological quality of each study and generated pooled effect size estimates using meta-analysis software. Of 997 articles identified, 20 met inclusion criteria for this review. Pain sensitivity testing used in these studies included chemical, electrical, mechanical, and thermal stimuli applied to various anatomical locations. Meta-analysis was appropriate for studies examining the immediate effect of SMT on mechanical pressure pain threshold (PPT). SMT demonstrated a favorable effect over other interventions on increasing PPT. Subgroup analysis showed a significant effect of SMT on increasing PPT at the remote sites of stimulus application supporting a potential central nervous system mechanism. Future studies of SMT related hypoalgesia should include multiple experimental stimuli and test at multiple anatomical sites.

Deep tissue hypersensitivity to pressure pain in individuals with unilateral acute inversion ankle sprain

OBJECTIVE

The objective of this study was to investigate whether pressure hypersensitivity over deep tissues is a feature of acute inversion ankle sprain.

DESIGN

This is a cross-sectional study.

SETTING

No study has previously investigated peripheral and central sensitization mechanisms in a clinical acute pain model such as inversion ankle sprain.

PATIENTS

Twenty individuals with unilateral inversion ankle sprain (10 women/10 men, age: 31 ± 7 years) and 19 comparable healthy controls (11 women/8 men, age: 30 ± 6 years) participated in this study.

OUTCOMES

Pressure pain thresholds (PPTs) over anterior talofibular, calcaneofibular, and deltoid ligaments; the lateral and medial malleolus; the tibialis anterior muscle; second metacarpal; and median, radial, and ulnar nerves were bilaterally assessed.

RESULTS

The analysis of variance (ANOVA) revealed that PPT levels over the affected anterior talofibular (P = 0.048) and calcaneofibular (P = 0.002) ligaments, and over the affected lateral malleolus (P < 0.001) were lower compared with the non-affected side within patients and both sides in controls. The patients also showed bilateral lower PPT levels over the deltoid ligament than controls (P < 0.05). No significant differences for PPT over the medial malleolus; the second metacarpal; the tibialis anterior muscle; and the median, ulnar, radial nerves were found. Significant negative correlations between intensity of ongoing pain and PPT over the anterior talofibular and deltoid ligaments were found: the higher the pain intensity, the lower the PPT.

CONCLUSIONS

This study showed the presence of localized pressure pain hypersensitivity over ankle ligaments in patients with unilateral acute inversion ankle sprain, confirming the presence of localized peripheral sensitization.

An increased response to experimental muscle pain is related to psychological status in women with chronic non-traumatic neck-shoulder pain

Background

Neck-shoulder pain conditions, e.g., chronic trapezius myalgia, have been associated with sensory disturbances such as increased sensitivity to experimentally induced pain. This study investigated pain sensitivity in terms of bilateral pressure pain thresholds over the trapezius and tibialis anterior muscles and pain responses after a unilateral hypertonic saline infusion into the right legs tibialis anterior muscle and related those parameters to intensity and area size of the clinical pain and to psychological factors (sleeping problems, depression, anxiety, catastrophizing and fear-avoidance).

Methods

Nineteen women with chronic non-traumatic neck-shoulder pain but without simultaneous anatomically widespread clinical pain (NSP) and 30 age-matched pain-free female control subjects (CON) participated in the study.

Results

NSP had lower pressure pain thresholds over the trapezius and over the tibialis anterior muscles and experienced hypertonic saline-evoked pain in the tibialis anterior muscle to be significantly more intense and locally more widespread than CON. More intense symptoms of anxiety and depression together with a higher disability level were associated with increased pain responses to experimental pain induction and a larger area size of the clinical neck-shoulder pain at its worst.

Conclusion

These results indicate that central mechanisms e.g., central sensitization and altered descending control, are involved in chronic neck-shoulder pain since sensory hypersensitivity was found in areas distant to the site of clinical pain. Psychological status was found to interact with the perception, intensity, duration and distribution of induced pain (hypertonic saline) together with the spreading of clinical pain. The duration and intensity of pain correlated negatively with pressure pain thresholds.

Thermal and pressure pain sensitivity in patients with unilateral shoulder pain: comparison of involved and uninvolved sides

STUDY DESIGN

Cross-sectional.

BACKGROUND

In the examination of patients with unilateral shoulder pain, pain provocation testing to compare the involved and uninvolved sides has been considered useful. However, side-to-side comparisons of experimental pain sensitivity in patients with unilateral shoulder pain are not widely reported in the literature.

OBJECTIVES

To compare experimental pain sensitivity between the involved and uninvolved sides in patients with unilateral shoulder pain.

METHODS

In consecutive patients seeking operative treatment for shoulder pain, sensitivity measures of bilateral pressure pain threshold at the shoulder and forearm, and thermal pain threshold, tolerance, and temporal summation at the forearm, were examined. Pressure sensitivity was tested with a Fischer pressure algometer, and thermal sensitivity with a computer-controlled Medoc neurosensory analyzer. The involved and uninvolved sides were compared with an analysis of variance. Influence of sex and location of testing were considered as covariates in the analysis.

RESULTS

Fifty-nine consecutively recruited participants completed experimental pain sensitivity testing. Participants reported significantly lower pressure pain thresholds in the involved side compared to the uninvolved side (F1,56 = 4.96, P = .030). In addition, female compared to male participants demonstrated lower pressure pain thresholds in the bilateral shoulder regions (F1,56 = 10.84, P = .002). There was no difference in thermal pain sensitivity between sides. Average clinical pain intensity was negatively correlated with pressure pain threshold at the involved local site (r = -0.284, P = .029), indicating an influence of clinical pain intensity on local pressure pain.

CONCLUSION

The results of this study provide evidence for higher experimental pressure pain sensitivity in the involved side of patients with unilateral shoulder pain and no difference between sides for thermal pain sensitivity. Females demonstrated higher pain sensitivity than males to pressure stimuli at the local shoulder region but not at the distal regions. Future studies should incorporate multiple stimuli when describing the pain profile of clinical populations.

Central sensitization: implications for the diagnosis and treatment of pain

Nociceptor inputs can trigger a prolonged but reversible increase in the excitability and synaptic efficacy of neurons in central nociceptive pathways, the phenomenon of central sensitization. Central sensitization manifests as pain hypersensitivity, particularly dynamic tactile allodynia, secondary punctate or pressure hyperalgesia, aftersensations, and enhanced temporal summation. It can be readily and rapidly elicited in human volunteers by diverse experimental noxious conditioning stimuli to skin, muscles or viscera, and in addition to producing pain hypersensitivity, results in secondary changes in brain activity that can be detected by electrophysiological or imaging techniques. Studies in clinical cohorts reveal changes in pain sensitivity that have been interpreted as revealing an important contribution of central sensitization to the pain phenotype in patients with fibromyalgia, osteoarthritis, musculoskeletal disorders with generalized pain hypersensitivity, headache, temporomandibular joint disorders, dental pain, neuropathic pain, visceral pain hypersensitivity disorders and post-surgical pain. The comorbidity of those pain hypersensitivity syndromes that present in the absence of inflammation or a neural lesion, their similar pattern of clinical presentation and response to centrally acting analgesics, may reflect a commonality of central sensitization to their pathophysiology. An important question that still needs to be determined is whether there are individuals with a higher inherited propensity for developing central sensitization than others, and if so, whether this conveys an increased risk in both developing conditions with pain hypersensitivity, and their chronification. Diagnostic criteria to establish the presence of central sensitization in patients will greatly assist the phenotyping of patients for choosing treatments that produce analgesia by normalizing hyperexcitable central neural activity. We have certainly come a long way since the first discovery of activity-dependent synaptic plasticity in the spinal cord and the revelation that it occurs and produces pain hypersensitivity in patients. Nevertheless, discovering the genetic and environmental contributors to and objective biomarkers of central sensitization will be highly beneficial, as will additional treatment options to prevent or reduce this prevalent and promiscuous form of pain plasticity.

Generalized expansion of nociceptive reflex receptive fields in chronic pain patients

Widespread central hypersensitivity is present in chronic pain and contributes to pain and disability. According to animal studies, expansion of receptive fields of spinal cord neurons is involved in central hypersensitivity. We recently developed a method to quantify nociceptive receptive fields in humans using spinal withdrawal reflexes. Here we hypothesized that patients with chronic pelvic pain display enlarged reflex receptive fields. Secondary endpoints were subjective pain thresholds and nociceptive withdrawal reflex thresholds after single and repeated (temporal summation) electrical stimulation. 20 patients and 25 pain-free subjects were tested. Electrical stimuli were applied to 10 sites on the foot sole for evoking reflexes in the tibialis anterior muscle. The reflex receptive field was defined as the area of the foot (fraction of the foot sole) from which a muscle contraction was evoked. For the secondary endpoints, the stimuli were applied to the cutaneous innervation area of the sural nerve. Medians (25-75 percentiles) of fraction of the foot sole in patients and controls were 0.48 (0.38-0.54) and 0.33 (0.27-0.39), respectively (P=0.008). Pain and reflex thresholds after sural nerve stimulation were significantly lower in patients than in controls (P<0.001 for all measurements). This study provides for the first time evidence for widespread expansion of reflex receptive fields in chronic pain patients. It thereby identifies a mechanism involved in central hypersensitivity in human chronic pain. Reverting the expansion of nociceptive receptive fields and exploring the prognostic meaning of this phenomenon may become future targets of clinical research.

Widespread mechanical pain hypersensitivity as a sign of central sensitization after breast cancer surgery: comparison between mastectomy and lumpectomy

OBJECTIVE

To investigate the differences in widespread pressure pain hypersensitivity after two surgery approaches for breast cancer: mastectomy or lumpectomy.

DESIGN

A cross-sectional blinded study.

SETTING

Widespread pressure pain hypersensitivity has been suggested as a sign of central sensitization. No study has previously investigated the presence of widespread pain pressure hypersensitivity after breast cancer surgery.

PATIENTS

Twenty-one women (age: 52±9 years old) who had received lumpectomy after breast cancer, 21 women (mean age: 50±10 years old) who had received mastectomy surgery after breast cancer, and 21 healthy women (age: 51±10 years old) participated.

OUTCOME MEASURES

Pressure pain thresholds (PPT) were bilaterally assessed over C5-C6 zygapophyseal joint, deltoid muscle, second metacarpal, and the tibialis anterior muscle.

RESULTS

Women with mastectomy had greater intensity of neck (t= -2.897; P=0.006) and shoulder/axillary (t= -2.609; P=0.013) pain as compared with those who received lumpectomy. The results showed that PPT were significantly decreased bilaterally over the C5-C6 zygapophyseal joint, deltoid muscle, second metacarpal, and tibialis anterior muscle in both lumpectomy and mastectomy groups as compared with healthy women in all points (P<0.001), without differences between both breast cancer groups (P=0.954). No significant differences in the magnitude of PPT levels between both breast cancer groups were found (all, P>0.450). PPT levels over some areas were negatively associated with the intensity of pain in the mastectomy, but not lumpectomy, group.

CONCLUSION

The current study found widespread pressure pain hyperalgesia in women who received breast cancer surgery suggesting central spreading sensitization. The degree of central sensitization was similar between lumpectomy and mastectomy surgery.

Specific mechanical pain hypersensitivity over peripheral nerve trunks in women with either unilateral epicondylalgia or carpal tunnel syndrome

STUDY DESIGN

Case-control study with blinded examiner.

OBJECTIVE

To investigate if pressure pain sensitivity is related to specific nerve trunks in the upper extremity of patients with either unilateral lateral epicondylalgia (LE) or carpal tunnel syndrome (CTS).

BACKGROUND

In the clinical setting, patients with LE tend to exhibit radial nerve trunk tenderness, whereas patients with CTS exhibit median nerve tenderness. No studies have investigated if specific nerve pressure pain hypersensitivity exists in patients with either LE or CTS.

METHODS

Sixteen women with unilateral LE (mean±SD age, 43±7 years), 17 women with unilateral CTS (43±6 years), and 17 healthy women (43±6 years) were included in this study. Pressure pain thresholds (PPT) were bilaterally assessed over the median, ulnar, and radial nerve trunks, as well as over the C5-6 zygapophyseal joints, by an examiner blinded to the subjectsí condition. A mixed-model analysis of variance was used to evaluate differences in PPT among groups (LE, CTS, or controls) and between sides (affected/nonaffected or dominant/nondominant).

RESULTS

The individuals in both the LE and CTS groups demonstrated lower PPT bilaterally over the median (group, P<.001; side, P=.437), radial (group, P<.001; side, P=.556), and ulnar (group, P<.001; side, P=.938) nerve trunks as compared to controls. Additionally, radial (P<.001) and ulnar (P=.005) nerves were more sensitive bilaterally in patients with LE than in patients with CTS. The median nerve was more sensitive bilaterally in patients with CTS than patients with LE (P=.002). Lower PPT over the cervical spine (group, P<.001; side, P=.233) were found bilaterally in both the LE and CTS groups. Further, patients with CTS exhibited lower cervical PPT than patients with LE (P<.001). PPT was negatively correlated with both pain intensity and duration of symptoms in both the LE and CTS groups (P<.001).

CONCLUSIONS

Bilateral mechanical nerve pain hypersensitivity is related to specific and particular nerve trunks in women with either unilateral LE or CTS. Our results suggest the presence of central and peripheral sensitization mechanisms in individuals with either LE or CTS.

Pressure pain sensitivity mapping in experimentally induced lateral epicondylalgia

PURPOSE

The aim of this study was to apply topographical techniques to investigate changes in pressure pain sensitivity after induction of delayed onset muscle soreness (DOMS) in the elbow region in healthy subjects.

METHODS

Pressure pain thresholds (PPT) were assessed over 12 points forming a 3 x 4 matrix (4 points in the superior part, 4 points in the middle, and 4 points in the lower part around the lateral epicondyle) over the dominant elbow in 13 healthy men, and pressure sensitivity maps were calculated. DOMS, as a model for lateral epicondylalgia (LE), was induced by repetitive high-level eccentric contractions of the wrist extensor muscles. PPT maps were assessed before, immediately after, and 24 h after eccentric exercise (DOMS).

RESULTS

The two-way repeated-measure ANOVA detected significant differences in mean PPT for the measurement points (F = 5.96, P < 0.001), with lower PPT over the points located over the extensor carpi radialis brevis muscle. There was also a significant effect of time (F = 121.3, P < 0.001) but no time x point location interaction (F = 0.7, P = 0.8). PPT were lower 24 h after (P < 0.001) but not immediately after (P > 0.05) eccentric exercise.

CONCLUSIONS

The study provides new key information regarding mechanical pain hyperalgesia in experimentally induced LE. Topographical pressure pain sensitivity maps from the elbow region revealed heterogeneously distributed mechanical sensitivity before and during DOMS. The most sensitive localizations for PPT assessment correspond to the muscle belly of the extensor carpi radialis brevis. Our results support the implication of the extensor carpi radialis brevis muscle in LE.

Generalized mechanical nerve pain hypersensitivity in children with episodic tension-type headache

OBJECTIVES

The objective of this study was to analyze the presence of generalized pressure pain hypersensitivity over nerve tissues in trigeminal and nontrigeminal regions in children with frequent episodic tension-type headache (FETTH).

METHODS

Thirty children, 7 boys and 23 girls (mean age: 8.8 +/- 1.7 years) with FETTH and 50 age- and gender-matched healthy children (14 boys, 36 girls; mean age: 8.5 +/- 2.1 years; P = .743) were recruited. Pressure pain thresholds (PPTs) were bilaterally assessed over supra-orbital (V1), infra-orbital (V2), mental (V3), median (C5), radial (C6), and ulnar (C7) nerves by an assessor who was blinded to the patient's condition.

RESULTS

The analysis of variance showed that PPT levels were significantly bilaterally decreased over both trigeminal (supra-orbital, infra-orbital, and mental) and nontrigeminal (median, ulnar, and radial) nerves in children with FETTH as compared with control subjects (all sites, P < .001). There was a greater magnitude of PPT decrease within trigeminal nerves as compared with nontrigeminal nerves (P < .03). PPTs over infra-orbital (r(s) = -0.4, P < .05) and radial (r(s) = -0.5, P < .01) nerves were negatively correlated with the duration of headache attacks (P < .05).

CONCLUSIONS

Our study revealed bilateral and generalized pressure hypersensitivity over both trigeminal and nontrigeminal nerves in children with FETTH. Diffuse hypersensitivity of peripheral nerves evidences the presence of hyperexcitability of the central nervous system in children with FETTH.

Sustained nociceptive mechanical stimulation of latent myofascial trigger point induces central sensitization in healthy subjects

The aim of the study is to test if sustained nociceptive mechanical stimulation (SNMS) of latent myofascial trigger points (MTrPs) induces widespread mechanical hyperalgesia. SNMS was obtained by inserting and retaining an intramuscular electromyographic (EMG) needle within a latent MTrP or a nonMTrP in the finger extensor muscle for 8 minutes in 12 healthy subjects. Pain intensity (VAS) and referred pain area induced by SNMS were recorded. Pressure pain threshold (PPT) was measured immediately before and after, and 10-, 20-, and 30-minutes after SNMS at the midpoint of the contralateral tibialis anterior muscle. Surface and intramuscular EMG during SNMS were recorded. When compared to nonMTrPs, maximal VAS and the area under VAS curve (VASauc) were significantly higher and larger during SNMS of latent MTrPs (both, P < .05); there was a significant decrease in PPT 10 minutes, 20 minutes, and 30 minutes postSNMS of latent MTrPs (all, P < .05). Muscle cramps following SNMS of latent MTrPs were positively associated with VASauc (r = .72, P = .009) and referred pain area (r = .60, P = .03). Painful stimulation of latent MTrPs can initiate widespread central sensitization. Muscle cramps contribute to the induction of local and referred pain.

PERSPECTIVE

This study shows that MTrPs are one of the important peripheral pain generators and initiators for central sensitization. Therapeutic methods for decreasing the sensitivity and motor-unit excitability of MTrPs may prevent the development of muscle cramps and thus decrease local and referred pain.

Sensitization in patients with painful knee osteoarthritis

Pain is the dominant symptom in osteoarthritis (OA) and sensitization may contribute to the pain severity. This study investigated the role of sensitization in patients with painful knee OA by measuring (1) pressure pain thresholds (PPTs); (2) spreading sensitization; (3) temporal summation to repeated pressure pain stimulation; (4) pain responses after intramuscular hypertonic saline; and (5) pressure pain modulation by heterotopic descending noxious inhibitory control (DNIC). Forty-eight patients with different degrees of knee OA and twenty-four age- and sex-matched control subjects participated. The patients were separated into strong/severe (VAS>or=6) and mild/moderate pain (VAS<6) groups. PPTs were measured from the peripatellar region, tibialis anterior (TA) and extensor carpi radialis longus muscles before, during and after DNIC. Temporal summation to pressure was measured at the most painful site in the peripatellar region and over TA. Patients with severely painful OA pain have significantly lower PPT than controls. For all locations (knee, leg, and arm) significantly negative correlations between VAS and PPT were found (more pain, more sensitization). OA patients showed a significant facilitation of temporal summation from both the knee and TA and had significantly less DNIC as compared with controls. No correlations were found between standard radiological findings and clinical/experimental pain parameters. However, patients with lesions in the lateral tibiofemoral knee compartment had higher pain ratings compared with those with intercondylar and medial lesions. This study highlights the importance of central sensitization as an important manifestation in knee OA.

Bilateral, wide-spread, mechanical pain sensitivity in children with frequent episodic tension-type headache suggesting impairment in central nociceptive processing

Introduction: The aim was to investigate bilateral, wide-spread pressure pain hyperalgesia in symptomatic (trigeminocervical) and non-symptomatic (pain-free distant) regions in children with frequent episodic tension-type headache (FETTH).

Methods: Twenty-five children, 6 boys and 19 girls (mean age, 8.9 ± 1.8 years) with FETTH and 50 age- and sex-matched healthy children (12 boys, 38 girls; mean age: 8.8 ± 1.7 years) were recruited. Pressure pain thresholds (PPTs) were bilaterally assessed over temporalis muscle, upper trapezius muscle, second metacarpal and tibialis anterior muscles in a blinded design.

Results: The results showed that PPT levels were significantly decreased bilaterally over the temporalis, upper trapezius and tibialis muscles, and the second metacarpal in children with FETTH as compared to controls (all sites, P < 0.001). No significant differences in the magnitude of PPT decrease between the upper trapezius muscle, second metacarpal and tibialis anterior muscles were found. PPT over both upper trapezius muscles were negatively correlated with the history and intensity of headache (rs = −0.415; P = 0.045).

Conclusions: The findings revealed bilateral, wide-spread pressure pain hypersensitivity in children with FETTH suggesting that wide-spread central sensitisation is involved in children with this headache pain condition.