Pressure pain threshold changes after repeated mechano-nociceptive stimulation of the trapezius muscle: possible influence of previous pain experience

Effect of percutaneous electrical stimulation with high-frequency alternating currents at 30 kHz on the sensory-motor system

Background

Unmodulated high-frequency alternating currents (HFAC) are employed for producing peripheral nerves block. HFAC have been applied in humans with frequencies up to 20 kHz, whether transcutaneously, percutaneously, or via surgically-implanted electrodes. The aim of this study was to assess the effect of percutaneous HFAC, applied with ultrasound-guided needles at 30 kHz, on the sensory-motor nerve conduction of healthy volunteers.

Methods

A parallel, double-blind, randomized clinical trial with a placebo control was conducted. Percutaneous HFAC at 30 kHz or sham stimulation was applied via ultrasound-guided needles in 48 healthy volunteers (n = 24 in each group) for 20 min. The assessed outcome variables were pressure pain threshold (PPT), mechanical detection threshold (MDT), maximal finger flexion strength (MFFS), antidromic sensory nerve action potential (SNAP), hand temperature, and subjective sensations by the participants. The measurements were recorded pre-intervention, during the stimulation (at 15 min), immediately post-intervention (at 20 min), and 15 min after the end of treatment.

Results

The PPT increased in the active group compared with sham stimulation, both during the intervention [14.7%; 95% confidence interval (CI): 4.4-25.0], immediately post-intervention (16.9%; 95% CI: -7.2-26.5), and 15 min after the end of the stimulation (14.3%; 95% CI: 4.4-24.3) (p < 0.01). The proportion of participants who reported feelings of numbness and heaviness was significantly higher in the active group (46 and 50%, respectively) than in the sham group (8 and 18%, respectively) (p < 0.05). No intergroup differences were observed in the remaining outcome variables. No unexpected adverse effects derived from the electrical stimulation were reported.

Conclusion

Percutaneous stimulation with HFAC at 30 kHz applied to the median nerve increased the PPT and subjective perception of numbness and heaviness. Future research should evaluate its potential therapeutic effect in people with pain.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT04884932, identifier NCT04884932.

Identifying Patients at High Risk of Chronic Pain After Video-Assisted Thoracoscopic Surgery Using Thermal Quantitative Sensory Testing

OBJECTIVE

To examine whether perioperative thermal quantitative sensory testing could be used to identify patients at high risk of chronic pain after video-assisted thoracoscopic surgery (VATS).

DESIGN

A single-center, prospective, observational study.

SETTING

At the Peking University People's Hospital.

PARTICIPANTS

A total of 111 patients scheduled to undergo VATS were enrolled.

INTERVENTIONS

Quantitative sensory testing was conducted at the anterior intercostal incision prior to surgery and after chest tube removal.

MEASUREMENTS AND MAIN RESULTS

The patient's chronic pain was assessed at 3 months after surgery using a questionnaire. The incidence of chronic pain was 35 out of 107 evaluable patients (32.7%). Among the 35 patients with chronic pain, 26 had features characteristic of neuropathic pain (74.3%). Compared to the patients without chronic pain, subjects with chronic pain had a significantly greater perioperative change in cold pain threshold (CPT; p = 0.032), but not cold detection threshold, warm detection threshold, and hot pain threshold . In the multivariate regression, perioperative CPT change was associated with chronic pain after VATS (odds ratio = 1.043, p = 0.026).

CONCLUSIONS

Chronic pain after VATS is typically neuropathic. The change in perioperative CPT at the incision site may help to identify patients at higher risk of chronic pain after VATS.

Pressure pain threshold mappings of the infraspinatus muscle in chronic unilateral shoulder pain patients do not reflect generalized hypersensitivity

OBJECTIVES

Increased mechanical sensitivity has been observed on the unaffected side in chronic pain conditions, suggesting generalized or widespread hypersensitivity. However, this cannot be considered as a universal response since this hypersensitivity is inconsistent across muscle pain pathologies. The aim of this study was to assess generalized hypersensitivity in chronic unilateral shoulder pain, using pressure pain threshold (PPT) mappings of the infraspinatus muscle. The proposed evaluation is based on the assessment of PPT on a limited subset of sites, reducing potential habituation or sensitization effects.

METHODS

Twenty-nine patients with unilateral shoulder pain (USP) and twenty-seven healthy volunteers were recruited. PPT was assessed using a manual pressure algometer. Six sites distributed over the infraspinatus muscle were assessed, and three repetitions were performed at each site. Mappings were derived using two-dimensional interpolation.

RESULTS

Lower PPT values were found in the symptomatic side in comparison with the asymptomatic side at all assessment sites (estimated difference: 1.42 ± 0.10 kgf/cm², p < 0.001), but there were no differences among the asymptomatic side of USP patients and any of the sides in healthy volunteers (largest estimated difference: 0.17 ± 0.28 kgf/cm², p = 0.927). Furthermore, the medial region of the infraspinatus muscle showed higher mechanical sensitivity in both healthy volunteers and USP patients.

CONCLUSIONS

These results suggest that USP does not induce generalized hypersensitivity, in contrast with previously reported findings. Physiotherapists could take these results into account for the assessment and treatment of patients with USP.

Robotic Stroking on the Face and Forearm: Touch Satiety and Effects on Mechanical Pain

Background: Slow stroking touch is generally perceived as pleasant and reduces thermal pain. However, the tactile stimuli applied tend to be short-lasting and typically applied to the forearm. This study aimed to compare the effects of a long-lasting brushing stimulus applied to the facial region and the forearm on pressure pain thresholds (PPTs) taken on the hand. Outcome measurements were touch satiety and concurrent mechanical pain thresholds of the hand. Methods: A total of 24 participants were recruited and randomized to receive continuous stroking, utilizing a robotic stimulator, at C-tactile (CT) favorable (3 cm/s) and non-favorable (30 cm/s) velocities applied to the right face or forearm. Ratings of touch pleasantness and unpleasantness and PPTs from the hypothenar muscle of the right hand were collected at the start of stroking and once per minute for 5 min. Results: A reduction in PPTs (increased pain sensitivity) was observed over time (P < 0.001). However, the increase in pain sensitivity was less prominent when the face was stroked compared to the forearm (P = 0.001). Continuous stroking resulted in a significant interaction between region and time (P = 0.008) on pleasantness ratings, with a decline in ratings observed over time for the forearm, but not on the face. Unpleasantness ratings were generally low. Conclusion: We observed touch satiety for 5 min of continuous robotic brushing on the forearm confirming previous studies. However, we did not observe any touch satiety for brushing the face. Mechanical pain sensitivity, measured in the hand, increased over the 5-min period but less so when paired with brushing on the face than with brushing on the forearm. The differential effects of brushing on the face and forearm on touch satiety and pain modulation may be by the differences in the emotional relevance and neuronal pathways involved.

Who is healthy? Aspects to consider when including healthy volunteers in QST--based studies-a consensus statement by the EUROPAIN and NEUROPAIN consortia

Clinical and human experimental pain studies often include so-called "healthy" controls in investigations of sensory abnormalities, using quantitative sensory testing (QST) as an outcome measure. However, the criteria for what is considered "healthy" vary among the different studies and between study centers and investigators, partly explaining the high variability of the results. Therefore, several aspects should be considered during inclusion of healthy volunteers in QST-based trials to have homogenous groups of healthy controls with less variability between human experimental studies, so that results are less likely to be false negative or false positive because of subject-related factors. The EUROPAIN and NEUROPAIN consortia aimed to define factors influencing the variability in selection of healthy subjects in QST-based studies before the start of both projects and to give recommendations how to minimize it based on the current literature and expertise of the participants. The present suggestions for inclusion criteria of healthy volunteers into QST-based trials describe a 2-level approach including standardized questionnaires enabling the collection of relevant information on sociodemographic data, medical history, current health status, coping strategies in dealing with pain, and the motivation of the volunteer to participate in the study. These suggestions are believed to help researchers interpret their results in comparison with others and improve the quality of clinical studies including healthy volunteers as controls or in human experimental pain studies. They aim to reduce any confounding factors. Furthermore, the acquired information will allow post hoc analyses of variance for different potential influencing factors.

Jaw dysfunction is associated with neck disability and muscle tenderness in subjects with and without chronic temporomandibular disorders

Purpose. Tender points in the neck are common in patients with temporomandibular disorders (TMD). However, the correlation among neck disability, jaw dysfunction, and muscle tenderness in subjects with TMD still needs further investigation. This study investigated the correlation among neck disability, jaw dysfunction, and muscle tenderness in subjects with and without chronic TMD. Participants. Forty females between 19 and 49 years old were included in this study. There were 20 healthy controls and 20 subjects who had chronic TMD and neck disability. Methods. Subjects completed the neck disability index and the limitations of daily functions in TMD questionnaires. Tenderness of the masticatory and cervical muscles was measured using an algometer. Results. The correlation between jaw disability and neck disability was significantly high (r = 0.915, P < 0.05). The correlation between level of muscle tenderness in the masticatory and cervical muscles with jaw dysfunction and neck disability showed fair to moderate correlations (r = 0.32–0.65). Conclusion. High levels of muscle tenderness in upper trapezius and temporalis muscles correlated with high levels of jaw and neck dysfunction. Moreover, high levels of neck disability correlated with high levels of jaw disability. These findings emphasize the importance of considering the neck and its structures when evaluating and treating patients with TMD.

Comparison of the short-term outcomes between trigger point dry needling and trigger point manual therapy for the management of chronic mechanical neck pain: a randomized clinical trial

STUDY DESIGN

Randomized clinical study.

OBJECTIVES

To compare the effects of trigger point (TrP) dry needling (DN) and TrP manual therapy (MT) on pain, function, pressure pain sensitivity, and cervical range of motion in subjects with chronic mechanical neck pain.

BACKGROUND

Recent evidence suggests that TrP DN could be effective in the treatment of neck pain. However, no studies have directly compared the outcomes of TrP DN and TrP MT in this population.

METHODS

Ninety-four patients (mean ± SD age, 31 ± 3 years; 66% female) were randomized into a TrP DN group (n = 47) or a TrP MT group (n = 47). Neck pain intensity (11-point numeric pain rating scale), cervical range of motion, and pressure pain thresholds (PPTs) over the spinous process of C7 were measured at baseline, postintervention, and at follow-ups of 1 week and 2 weeks after treatment. The Spanish version of the Northwick Park Neck Pain Questionnaire was used to measure disability/function at baseline and the 2-week follow-up. Mixed-model, repeated-measures analyses of variance (ANOVAs) were used to determine if a time-by-group interaction existed on the effects of the treatment on each outcome variable, with time as the within-subject variable and group as the between-subject variable.

RESULTS

The ANOVA revealed that participants who received TrP DN had outcomes similar to those who received TrP MT in terms of pain, function, and cervical range of motion. The 4-by-2 mixed-model ANOVA also revealed a significant time-by-group interaction (P<.001) for PPT: patients who received TrP DN experienced a greater increase in PPT (decreased pressure sensitivity) than those who received TrP MT at all follow-up periods (between-group differences: posttreatment, 59.0 kPa; 95% confidence interval [CI]: 40.0, 69.2; 1-week follow-up, 69.2 kPa; 95% CI: 49.5, 79.1; 2-week follow-up, 78.9 kPa; 95% CI: 49.5, 89.0).

CONCLUSION

The results of this clinical trial suggest that 2 sessions of TrP DN and TrP MT resulted in similar outcomes in terms of pain, disability, and cervical range of motion. Those in the TrP DN group experienced greater improvements in PPT over the cervical spine. Future trials are needed to examine the effects of TrP DN and TrP MT over long-term follow-up periods.

LEVEL OF EVIDENCE

Therapy, level 1b.

An improvement of mechanical pain sensitivity measurement method: the smaller sized probes may detect heterogeneous sensory threshold in healthy male subjects

OBJECTIVE

On the basis of our experience in the application of the mechanical algometer and a number of pilot experiments, we speculated that 0.1- and 0.01-cm(2) probes might improve the measurement of mechanical pain sensitivity relative to the conventional 1-cm(2) probe. Here, we examined the accuracy, feasibility, and applicability of these probes in detecting the mechanical pain sensitivity.

DESIGN

Mechanical pain threshold and tolerance tests were performed on subjects using the three probes of 1, 0.1, and 0.01 cm(2) in random order. We compared the application of these probes.

SETTING

The study was set at the Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.

SUBJECTS

Fifty healthy male Han Chinese subjects were recruited.

OUTCOME MEASURES

We compared the qualities of stimulus-evoked pain, test stability, the measuring time, the subjects' acceptance level of the procedure, the validity of pain measurement, and the arduousness of the task for the investigator among the three different size probes.

RESULTS

Compared with the conventional 1-cm(2) probe, the 0.01- and 0.1-cm(2) probes resulted in the subjects responding to stimulus-evoked pain more quickly, accurately, and consistently, and also made the measurement more comfortable for investigators. Up to 80% of the subjects reported the pain quality as a pricking sensation when the 0.01-cm(2) probe was used.

CONCLUSION

The use of the 0.1-cm(2) probe might be more suitable as an optimized method for the detection of pressure pain sensitivity in clinical studies. In addition, the 0.01-cm(2) probe could potentially serve as an alternative to the weighted needle pinprick, providing continuous quantizing detection for pricking pain sensitivity.

Sensory functions in the foot soles in victims of generalized torture, in victims also beaten under the feet (falanga) and in healthy controls - A blinded study using quantitative sensory testing

Background

Falanga torture (beatings on the foot soles) produces local chronic pain and severe walking difficulties. We have previously reported signs of neuropathic pain in the feet of falanga victims. The objective here was to clarify underlying pain mechanisms by quantifying sensory impairments in the feet of torture victims who had experienced both generalized torture and those who had been exposed to falanga in addition. An ethnically matched control group was available.

Methods

We employed quantitative sensory testing (QST) by investigators blinded to whether the patients, 32 male torture victims from the Middle East, had (n=15), or had not (n=17) been exposed to falanga. Pain intensity, area and stimulus dependence were used to characterize the pain as were interview data on sensory symptoms. QST included thresholds for touch, cold, warmth, cold-pain, heat-pain, deep pressure pain and wind-up to cutaneous noxious stimuli in the foot soles. Clinical data on anxiety and depression were retrieved.

Results

Almost all falanga victims had moderate or strong pain in their feet and in twice as large an area of their foot soles as other torture victims. One-third of the latter had no pain in their feet and many reported slight pain; in spite of this, there were no differences in foot sole QST data between the tortured groups. A comparison with normal data indicated that both tortured groups had hypoesthesia for all cutaneous sensory fibre groups except those transmitting cold and heat pain, in addition to deep mechano-nociceptive hyperalgesia.

Conclusion

A comparison of the QST data between victims having been exposed to generalized torture and victims who in addition had been exposed to falanga, showed no differences on the group level. The sensory disturbances in relation to our control group are compatible with central sensitization and de-sensitization, pointing to a core role of central mechanisms. A further analysis to create individual sensory profiles from our measurements is in progress.

Deep tissue hyperalgesia after computer work

Background and purpose

A growing number of people are using computers. Shoulder and neck pain occur commonly during computer work. Peripheral and central sensitization may play a major role in establishing and maintaining several chronic pain conditions. We have previously reported that a 90 min simulated computer office-work induced substantial pain in the shoulders and neck. We hypothesized that the development of pain during the computer work may be related to sensitization. The aim of the present study was to examine if the 90 min computer work induced deep tissue muscle hyperalgesia manifested as altered pressure pain thresholds (PPTs).

Methods

Twenty-two subjects with chronic shoulder and neck pain (pain group) and 26 healthy and pain free subjects (reference group) performed a standardized computer office-work task with use of a computer-mouse and with time pressure and high precision demands continuously for 90 min. The pressure pain threshold was measured with a pressure algometer in shoulder and forearm muscles (bilaterally in upper trapezius and extensor carpi radialis), and at sternum, before and 15 min and 30 min after the computer work task.

Results

The PPTs before starting the computer work were not different between the groups at any of the five locations. In both groups, the PPTs in the active and inactive side of the upper trapezius as well as in the extensor carpi radialis of the forearm operating the computer mouse were significantly reduced after the 90 min computer work compared with the pre-work levels. In the pain group, also the PPT in the inactive resting forearm was significantly reduced. The changes seen in PPTs from pre-to post-work were not significantly different between the groups, except for the inactive resting forearm where the groups exhibited different time course.

Conclusion

A decrease in pressure pain thresholds of involved muscles suggests that computer office-work can induce deep tissue hyperalgesia within 90 min. The development of pain during the computer work indicates peripheral sensitization as the predominant mechanism. Decreased pressure pain thresholds also in sites distant from pain areas may indicate a contribution from central sensitization in the subjects with chronic shoulder and neck pain.

Implications

The lasting pain after work and the reduced PPTs both in involved and distant musculature may indicate need for frequent pauses during computer work, especially when performed with time pressure and high precision demands, in order to avoid pain to increase and sustain after work, and thus to prevent the possibility of pain to become chronic.

Pressure pain sensitivity maps of the neck-shoulder and the low back regions in men and women

Background

Musculoskeletal pain in the low back and neck-shoulder regions is a major problem among the working population all over the world. The prevalence of musculoskeletal pain is found to be higher among women. Women also have lower pressure pain thresholds (PPTs) than men. Pressure pain topography aims at mapping the spatial distribution of PPT within a muscle in an attempt to track changes in mechanical sensitivity. In order to assess gender differences in the pain topography, it is necessary to map the distribution in both healthy men and women. The aim of this study was to assess PPT maps from the cervico-thoracic and lumbar regions in men and women.

Methods

Eleven men and eleven women without any known musculoskeletal disorders participated in the study. PPT was measured twice at 36 points over the trapezius muscle of the dominant arm, at 36 points over the trapezius muscle on the contralateral side and at 12 points over the spine between the left and right trapezius. Further, 11 points were measured over the erector spinae muscle on the left side of the spine between the first and the fifth lumbar vertebrae, 11 on the right side and 5 points on the spine itself. The measurements on each trapezius muscle were divided according to anatomical subdivisions. Three-way and two-way ANOVAs were used to analyse the differences in PPTs with the following factors: gender, locations and sub-divisions (only for cervico-thoracic region).

Results

There were no differences between left and right side in neither the cervico-thoracic nor the lumbar region, but there were (large effect) differences between the subdivisions in the trapezius with the lowest values in the upper part (P < 0.001; partial η² = 0.19). Women had (small effect) lower PPT in both cervico-thoracic and lumbar regions (P ≤ 0.001; partial η² = 0.02 for both regions), but gender had no effect on neither location nor subdivisions.

Conclusions

The pain topography was not found to be different between genders in the cervico-thoracic and lumbar regions. This study can be used as basis for further clinical studies on musculoskeletal disorders.

Gender and site of injection do not influence intensity of hypertonic saline-induced muscle pain in healthy volunteers

The aim of the study was to determine whether the same stimulus to different muscles results in comparable pain and whether gender has any influence on the pain. We compared the quality and intensity of muscle pain induced by a hypertonic saline injection into the tibialis anterior (leg) muscle to that after an injection into the lumbar erector spinae (back) muscle in both male (n=10) and female (n=10) volunteers. Hypertonic or isotonic saline was injected into the leg and back muscles and pain intensity (visual analogue scale, VAS) and pain quality (McGill Pain Questionnaire) were measured. Pressure pain tolerance around the site of injection and on the contralateral side was measured. Hypertonic saline injection induced significant muscle pain in the back and leg compared to isotonic saline (P<0.05, ANOVA). The site of injection did not influence the quality of pain but there was a gender bias in the descriptive words chosen (chi(2) test, P<0.05) and female subjects were more sensitive to pressure than male subjects. Experimentally induced muscle pain is equivalent in intensity and quality in the leg and back muscle. Gender does not influence muscle pain intensity but does influence sensitivity to pressure and the description of pain.

Clinical findings in men with chronic pain after falanga torture

OBJECTIVES

To explore clinical findings in men with chronic pain after falanga torture as compared with controls, and to try to understand the nature of the pain mechanisms responsible.

METHODS

Eleven male torture victims from the Middle East with chronic pain after falanga, and 11 age, sex, and ethnically matched controls with no history of torture were recruited. All participants were interviewed regarding pain characteristics in the feet and lower legs at rest and when walking. Structural changes and motor and sensory function were clinically assessed according to a standardized protocol. The walking pattern was observed for compensatory gait patterns.

RESULTS

The torture victims had pain in their feet and lower legs and a compensated gait pattern, usually with severe pain during walking. Reduced light touch and thermal sensation, tactile dysesthesia, allodynia, and tenderness on palpation were common findings. Structural changes in the feet were found in more than half of the victims, but did not correlate with pain reports. These clinical findings were nonexistent or seen only rarely in controls.

DISCUSSION

We found clear clinical signs of nerve injury in the feet. The sensory findings indicated 2 neuropathic pain mechanisms, one dominated by a peripheral pain generator and other by irritative phenomena (dysesthesia, allodynia), indicating central sensitization. It is reasonable to assume that these changes are due to the falanga exposure. A nociceptive contribution cannot be excluded. It is important to perform an individual diagnostic analysis to facilitate adequate treatment.