Somatosensory perception in a remote pain-free area and function of diffuse noxious inhibitory controls (DNIC) in patients suffering from long-term trapezius myalgia.

In patients with localized musculoskeletal pain, spread of pain and tenderness outside the primarily painful area and sometimes even generalization of pain have been reported, the latter possibly indicating a dysfunction of endogenous pain modulatory systems. The purpose of the study was to use patients with long-term trapezius myalgia as a model to investigate the possible influence of a localized muscle pain on somatosensory processing in a remote pain-free area and the effect of heterotopic noxious conditioning stimulation (HNCS) on 'diffuse noxious inhibitory controls' (DNIC) related mechanisms. Altered somatosensory processing may indicate subclinical derangement of endogenous modulatory systems. Ten patients with long-term (> or = 1 year) trapezius myalgia and 10 age- and sex-matched healthy controls participated. Pressure pain sensitivity, low threshold mechanoreceptive function and thermal sensitivity, including thermal pain, were assessed at the right thigh before, during and following HNCS. Pain was induced in the forearm by the tourniquet test. At rest allodynia to pressure was found at the thigh in conjunction with hypoaesthesia to cold (p<0.03 and p<0.01 respectively), in patients compared with controls. During HNCS, the sensitivity to pressure pain and suprathreshold heat pain decreased in patients and controls alike (p<0.02 and p<0.04 respectively) and returned to baseline following HNCS. In conclusion, in a remote non-painful area allodynia to pressure and hypoaesthesia to cold were found in conjunction with preserved function of DNIC-related mechanisms. Whether altered central somatosensory processing at rest may indicate a predisposition for further spread of pain is at present unclear.     

Somatosensory perception and function of diffuse noxious inhibitory controls (DNIC) in patients suffering from rheumatoid arthritis.

The purpose was to investigate the influence of ongoing pain from an inflammatory nociceptive pain with two different disease durations on somatosensory functions and the effect of heterotopic noxious conditioning stimulation (HNCS) on 'diffuse noxious inhibitory controls' (DNIC) related mechanisms. Eleven patients with rheumatoid arthritis of a short duration (<1 year) (RA1), and 10 patients with rheumatoid arthritis of longer duration (>5 years) (RA5) as well as 21 age- and sex-matched healthy controls participated. Pressure pain sensitivity, low threshold mechanoreceptive function and thermal sensitivity, including thermal pain, were assessed over a painful and inflamed joint as well as in a pain-free area, i.e. the right thigh before HNCS (cold-pressor test) and repeated at the thigh only during and following HNCS. In RA1 and RA5 allodynia to pressure was seen over the joint (p<0.02 and p<0.001 respectively) in conjunction with hypoaesthesia to light touch (p<0.02) and hyperaesthesia to innocuous cold (p<0.05) in RA5. At the thigh, allodynia to pressure was found in RA5 (p<0.002). During HNCS, the sensitivity to pressure pain decreased in patients and controls alike (p<0.001). In conclusion, over an inflamed joint allodynia to pressure was found in both RA groups, with additional sensory abnormalities in RA5. In a non-painful area, allodynia to pressure was found in RA5, suggesting altered central processing of somatosensory functions in RA5 patients. The response to HNCS was similar in both RA groups and controls, indicating preserved function of DNIC-related mechanisms.     

Time dependent differences in pain sensitivity during unilateral ischemic pain provocation in healthy volunteers.

Plurisegmental endogenous pain inhibitory mechanisms related to diffuse noxious inhibitory controls (DNIC) were demonstrated in animal experiments to act on multireceptive neurons of the entire cord outside the conditioned segment without any side differences. Human experiments have demonstrated altered pain sensitivity to pressure, heat and electrical stimulation during heterotopic noxious conditioning stimulation (HNCS). The purpose of the study was to examine if side and/or time differences in pain thresholds and suprathreshold pain sensitivity for pressure and heat, respectively, could be detected during HNCS. Perception thresholds to pressure and heat pain as well as the sensitivity to suprathreshold pressure (SPP) and heat pain (SHP) were assessed in 18 healthy volunteers bilaterally at the thighs before, during and following ischemia-induced pain of the left forearm (HNCS). The assessments started with either the right (10 subjects) or the left thigh (8 subjects). During HNCS the pressure pain threshold increased significantly (p<0.001) on both sides alike. No significant difference in the magnitude of the altered pressure pain threshold was seen between sides for the first or the lastly assessed side. On the lastly assessed side only SPP and SHP increased significantly on both sides alike (p<0.02 and p<0.03, respectively), without magnitude differences between sides. During unilateral HNCS of the left arm, a time factor was demonstrated only for alterations in suprathreshold pain sensitivity, without any differences in magnitude between sides. Therefore, the results have implications for future design of HNCS-related experimental and clinical studies.     

Different patterns of blood flow response in the trapezius muscle following needle stimulation (acupuncture) between healthy subjects and patients with fibromyalgia and work-related trapezius myalgia.

Needle stimulation (acupuncture) has recently been shown to increase blood flow in the tibialis anterior muscle and overlying skin in healthy subjects (HS) and patients with fibromyalgia (FM). The aim of the present study was to examine the effect of needle stimulation on local blood flow in the trapezius muscle and overlying skin in HS and two groups of patients suffering from chronic pain in the trapezius muscle, i.e., FM and work-related trapezius myalgia (TM) patients. Two modes of needling, deep muscle stimulation (Deep) and subcutaneous needle insertion (SC), were performed at the upper part of the shoulder and blood flow was monitored for 60 min post-stimulation. Blood flow changes were measured non-invasively by using a new application of photoplethysmography. Increased blood flow in the trapezius muscle and overlying skin was found in all three groups following both Deep and SC. In HS, Deep was superior to SC in increasing skin and muscle blood flow, whereas in FM, SC was as effective as, or even more effective, than Deep. In the severely affected TM patients, no differences were found between the stimuli, and generally, a lesser blood flow response to the stimuli was found. At Deep, the muscle blood flow increase was significantly larger in HS, compared to the two patient groups. Positive correlations were found between muscle blood flow at Deep and pressure pain threshold in the trapezius muscle, neck movement and pain experienced at the stimulation, and negative correlations were found with spontaneous pain-related variables, symptom duration and age, pointing to less favorable results with worsening of symptoms, and to the importance of nociceptor activation in blood flow increase. It was hypothesized that the different patterns of muscle blood flow response to the needling may mirror a state of increased sympathetic activity and a generalized hypersensitivity in the patients. The intensity of stimulation should be taken into consideration when applying local needle stimulation (acupuncture) in order to increase the trapezius muscle blood flow in chronic pain conditions.     

The influence of pain intensity on somatosensory perception in patients suffering from subacute/chronic lateral epicondylalgia.

A confounding factor in the analysis of chronic pain patients is the finding of signs of somatosensory disturbances not only in neuropathic pain patients but also in a subgroup of patients with musculoskeletal pain. The purpose was to investigate if patients suffering from subacute/chronic lateral epicondylalgia demonstrated altered sensibility, and if this was affected by pain intensity. At the start of the experiment, quantitative sensory testing (QST) (thermal, pressure pain, touch) was performed in the local pain area and in the area of pain referral. QST was repeated following pain provocation (weight lifting). A local anaesthetic was then injected into the lateral epicondyle and QST was repeated in the area of pain referral. The contralateral arm was assessed, treated and injected in the same way. At the baseline assessment there was no difference in sensibility between sides, with the exception of a significantly lowered threshold to noxious heat (p<0.04) in the area of pain referral, present during the whole experiment. In the affected arm only, weight lifting resulted in significantly increased pain intensity in the local (p<0.01) and referred (p<0.01) pain areas, respectively. Repeated muscle contractions resulted in altered somatosensory functions in both the affected arm and the unaffected arm, consequently not dependent on ongoing pain in the assessed area. Tactile perception thresholds increased significantly following pain provocation in the area of pain referral (p<0.04) only and normalized following injection of local anaesthetic (p<0.02), indicating that the sensitivity to light touch was altered by the nociceptive input from the affected arm.     

Quantitative sensory testing in the German Research Network on Neuropathic Pain (DFNS): Somatosensory abnormalities in 1236 patients with different neuropathic pain syndromes

Neuropathic pain is accompanied by both positive and negative sensory signs. To explore the spectrum of sensory abnormalities, 1236 patients with a clinical diagnosis of neuropathic pain were assessed by quantitative sensory testing (QST) following the protocol of DFNS (German Research Network on Neuropathic Pain), using both thermal and mechanical nociceptive as well as non-nociceptive stimuli.     

Somatosensory function in patients with and without pain after traumatic peripheral nerve injury

Why traumatic injuries to the peripheral nervous system infrequently result in neuropathic pain is still unknown. The aim of this study was to examine the somatosensory system in patients with traumatic peripheral nerve injury with and without pain to try to unravel possible links to mechanisms underlying development and maintenance of pain. Eighteen patients with spontaneous ongoing pain and 16 patients without pain after unilateral partial peripheral traumatic nerve injury were studied. In the area of partial denervation and in the corresponding contralateral area perception thresholds to warmth, cold, light touch, pressure pain, cold‐ and heat pain were assessed as were pain intensities at suprathreshold heat pain stimulation. Comparing sides patients with pain reported allodynia to cold (p = 0.03) and pressure (p = 0.016) in conjunction with an increase in the perception threshold to non‐painful warmth (p = 0.024) on the injured side. Pain‐free patients reported hypoesthesia to light touch (p = 0.002), cold (p = 0.039) and warmth (p = 0.001) on the injured side. There were no side differences in stimulus–response functions using painful heat stimuli in any of the groups. In addition, no significant difference could be demonstrated in any sensory modality comparing side‐to‐side differences between the two groups. In conclusion, increased pain sensitivity to cold and pressure was found on the injured side in pain patients, pointing to hyperexcitability in the pain system, a finding not verified by a more challenging analysis of side‐to‐side differences between patients with and without pain.     

Abnormalities of somatosensory perception in patients with painful osteoarthritis normalize following successful treatment.

To investigate the effect of chronic nociceptive pain on somatosensory perception, quantitative sensibility testing was performed in the most painful area and the homologous contralateral side in 14 patients with painful osteoarthritis of the hip. Twelve patients were reassessed in a painfree state 6-14 months following surgery. Von Frey filaments were used to test low-threshold mechanoreceptive function. Pressure pain sensitivity was assessed with a pressure algometer and thermal sensitivity with a Thermotest. Sex- and age-matched controls were examined in the corresponding areas at similar time intervals. There was no statistically significant difference between groups in the sensitivity to light touch and innocuous cold in either session. Compared to controls, patients had increased sensitivity to pressure pain in the most painful area (p < 0.002), bilaterally increased sensitivity to innocuous warmth (p < 0.03), cold pain (p< 0.05) and a tendency toward bilaterally increased sensitivity to heat pain (p = 0.054) before surgery. In the painful area, patients' sensitivity to pressure pain decreased (p < 0.04) and, remaining within normal limits, sensitivity to light touch increased (p < 0.006) compared to values prior to surgery. No statistically significant differences between the groups were seen following surgery, indicating that the sensibility changes had been maintained by chronic nociceptive pain.     

The influence of experimental pain intensity in the local and referred pain area on somatosensory perception in the area of referred pain

The aim of this study was to investigate the influence of experimental pain intensity in the local and referred pain area on somatosensory perception thresholds in the area of referred pain. Pain was induced by intramuscular electrical stimulation of the left infraspinatus muscle in 12 healthy individuals. The stimulation corresponded to the local pain threshold ("mild local pain"), the referred pain threshold ("mild referred pain"), and a pain intensity corresponding to 2 on a 10-point category scale in the referred pain area ("moderate referred pain"). Quantitative sensory testing was performed to assess perception thresholds in the referred pain area and the homologous contralateral area before and during stimulation. Perception thresholds to light touch (LTTs), pressure pain (PPTs), and to innocuous as well as noxious warmth and cold were assessed. During stimulation the LTTs increased in the referred pain area compared to baseline, uninfluenced by pain intensity. Perception thresholds to innocuous cold and warmth increased bilaterally during the stimulation, without relation to pain intensity. Heat pain thresholds were not affected. Compared to baseline, PPTs increased bilaterally during stimulation corresponding to "mild local pain" and "mild referred pain", respectively, and a further increase was seen during "moderate referred pain". The decreased sensitivity to innocuous cold, warmth, and pressure pain was bilateral, indicating activation of endogenous net inhibitory mechanisms interacting bilaterally. We found no influence of pain intensity on somatosensory thresholds restricted to the referred pain area and light touch was the only affected modality in the referred pain area only.     

Experimental muscle pain provokes long-lasting alterations of thermal sensitivity in the referred pain area.

This study explores thermal sensitivity and thermal nociception for signs of central sensitization in the area of referred muscle pain. Two groups of 24 healthy subjects (ss) each, and with mean ages of, respectively, 27 and 55 years, were first trained in quantitative sensory testing and pain rating. Then, in a second session, referred pain was evoked by injection of 6% hypertonic saline into the infraspinatus muscle. Cold and warm thresholds, synthetic heat threshold (SHT--evoked by an alternating pattern of adjacent cold and warmth), and thermal pain thresholds were measured within the referred pain area at a rate of 1/20 min for 60-120 min. All ss of both groups experienced referred pain mostly in the upper arm and of medium intensity. Pain lasted for approximately 12min with a shorter duration in the older group (p<0.02). The cold threshold increased significantly (p<0.001), and the warm threshold slightly, after the injection and remained high for the whole observation period (i.e. lower and higher temperatures were necessary to elicit cold and warmth, respectively). Threshold recovery was more delayed in the older age group. Of those 28 ss in whom cold pain threshold could be followed during the whole observation period, 18 ss showed an immediate threshold decrease of average 6 degrees C which outlasted the observation period. Four ss responded with a threshold increase. Heat pain thresholds were not affected in the referred pain area. Average synthetic heat threshold did not change; there were, however, distinct and lasting individual threshold shifts in either direction. Ss with lowered cold pain thresholds or evident threshold shifts for synthetic heat had also higher pain ratings. The results demonstrate that experimental muscle pain can induce long-lasting changes in thermal sensitivity and nociception. The unexpected cold threshold increase may tentatively be explained as an expression of long-term depression. The decrease of cold pain threshold or SHT in subgroups of ss may indicate central sensitization. However, the observed changes in this experiment do not provide an unambiguous indicator for central sensitization which seems to be rather individual and might depend on pain intensity and proneness to express central mechanisms of sensitization. Therefore in clinical pain states the individual pattern of sensory abnormalities has to be analysed and interpreted in addition to the pain parameters to assess central involvement.     

Dysfunction of endogenous pain inhibition during exercise with painful muscles in patients with shoulder myalgia and fibromyalgia

The aim of this study was to investigate how exercise influenced endogenous pain modulation in healthy controls, shoulder myalgia patients and fibromyalgia (FM) patients. Twenty-one healthy subjects, 20 shoulder myalgia patients and 20 FM patients, all females, participated. They performed standardized static contractions, that is, outward shoulder rotation (m. infraspinatus) and knee extension (m. quadriceps). Pressure pain thresholds (PPTs) were determined bilaterally at m. infraspinatus and m. quadriceps. During contractions PPTs were assessed at the contracting muscle, the resting homologous contralateral muscle and contralaterally at a distant site (m. infraspinatus during contraction of m. quadriceps and vice versa). Myalgia patients had lower PPTs compared to healthy controls at m. infraspinatus bilaterally (p < 0.01), but not at m. quadriceps. FM patients had lower PPTs at all sites compared to healthy controls (p < 0.001) and myalgia patients (p < 0.001). During contraction of m. infraspinatus PPTs increased compared to baseline at the end of contraction in healthy controls (all sites: p < 0.003), but not in myalgia or FM patients. During contraction of m. quadriceps PPTs increased compared to baseline at the end of contraction in healthy controls (all sites: p < 0.001) and myalgia patients (all sites: p < 0.02), but not in FM patients. In conclusion, we found a normal activation of endogenous pain regulatory mechanisms in myalgia patients during contraction of the non-afflicted m. quadriceps, but a lack of pain inhibition during contraction of the painful m. infraspinatus. FM patients failed to activate their pain inhibitory mechanisms during all contractions.     

Homotopic stimulation can reduce the area of allodynia in patients with neuropathic pain

Allodynia is a common, troublesome feature of neuropathic pain conditions. In a previous study of postherpetic neuralgia we observed that repeated tactile stimulation appeared to reduce the size of the area of allodynia in some patients. We have undertaken a pragmatic clinical study to characterise this phenomenon in neuropathic pain patients with a range of different aetiologies.Neuropathic pain patients with a discrete area of tactile allodynia were recruited (n = 20). We assessed the sensitive area using punctate and dynamic tactile stimuli, and thermal quantitative sensory testing. On two separate testing visits, the patients had repeated (10× over 1 min) noxious heat or cotton bud strokes applied to the affected site or contralaterally.Tactile stimulation of the affected area evoked pain (median 7 NRS) and a reduction (>30%) in the area of allodynia in 9/18 patients (maximum −48 ± 9%, after 20 min), although the intensity of allodynic pain was unchanged. This effect persisted for over 1 h and was present the following day in all patients tested (n = 5/5). No subjects showed an increase in area after allodynic stimulation. There was no change in heat pain threshold at a distant site following allodynic stimulation, suggesting no activation of diffuse noxious inhibitory control. Repeated thermal noxious stimulation (median NRS 7) could also elicit changes (>30%) in the area of allodynia in some patients (reductions in 7/20, increases in 3/20).Thus, we have found that a brief period of homotopic painful stimulation can reduce the area of allodynia in around half of patients with established neuropathic pains.     

Long-term consequences of early infant injury and trauma upon somatosensory processing.

Long-term consequences of early infant injury upon somatosensory processing were tested in school aged children. The aim was to test whether the long-term changes in sensitivity reported in animal models, in regions both local to and distant from the injury site, could be observed in humans. To do this we used quantitative sensory testing (QST) in children aged 9-12 years who had undergone cardiac surgery in infancy. Cutaneous mechanical and thermal thresholds were measured at the thoracic scar region and at control contralateral thoracic and reference thenar areas in this early surgery group (n=9), and compared with thresholds at the same regions in age and gender-matched controls (n=9). The results showed that the cardiac surgery group was significantly less sensitive to von Frey hair tactile stimulation in the non-injured thenar area than the control group; mean threshold 5.02, SD+/-1.59 compared to 2.76, SD+/-0.79 (von Frey hair number, p=0.04). In addition, their lateral thoracotomy scar areas were significantly less sensitive to von Frey hair stimulation (mean=9.82, SD+/-1.97, p<0.001) and to cooling and warming than any other site tested. Eight of the nine children in the early surgery group did not perceive warmth on their scars and were only able to detect uncomfortable heat as the temperature was raised. Three of these children felt a paradoxical cold prior to the hot sensation and all reported subtle abnormalities in everyday sensations. Questionnaires revealed perceived differences in pain perception, individual aberrant sensations and pain interfering with daily life that warrant further study. We conclude that tissue injured in early infancy remains measurably altered to mechanical and thermal stimulation in later life. These findings are consistent with the results of animal studies that early infant injury has not only local, but also global long-term consequences upon sensory processing.     

Comparison of muscle and joint pressure-pain thresholds in patients with complex regional pain syndrome and upper limb pain of other origin

Pain localized in the deep tissues occurs frequently in complex regional pain syndrome (CRPS). In addition, hyperalgesia to blunt pressure over muscles is common in CRPS, but it often appears in limb pain of other origin as well. Considering that 3-phase bone scintigraphy (TPBS) reveals periarticular enhanced bone metabolism in CRPS, joint-associated hyperalgesia to blunt pressure might be a more specific finding than hyperalgesia over muscles. In 34 patients with upper limb pain (18 CRPS, 16 non-CRPS; diagnosed in accordance to the Budapest criteria) and in 18 healthy controls, pressure-pain thresholds (PPT) were assessed bilaterally over the thenar (PPT_Thenar), the metacarpophalangeal (PPT_MCP), and the proximal interphalangeal (PPT_PIP) joints using a pressure algometer (Somedic, Sweden). Beforehand, all patients had received TPBS for diagnostic purposes independently of the study. Region-of-interest (ROI) ratios (mineralization phase) for the MCP and PIP, excluding fracture sites, were correlated with the PPT. In CRPS, all ROI ratios were significantly increased and all PPT of the affected hand were decreased compared to non-CRPS (PPT_Thenar: 243 ± 150 kPa vs 358 ± 197 kPa, PPT_MCP: 80 ± 67 kPa vs 159 ± 93 kPa, PPT_PIP: 80 ± 56 kPa vs 184 ± 110 kPa; P < .01) and controls (PPT_Thenar: 478 ± 106 kPa, PPT_MCP: 254 ± 50 kPa, PPT_PIP: 275 ± 76 kPa; P < .01). A PPT_Thenar below 293 kPa revealed 77% sensitivity but only 63% specificity, whereas a PPT_PIP below 102 kPa had 82% sensitivity and 94% specificity to identify CRPS. Only in CRPS were PPT_MCP and PPT_PIP correlated significantly inversely with the ROI ratio (MCP: r = −0.439, PIP: r = −0.447). PPT_PIP shows higher specificity for CRPS type I than PPT_Thenar without loss of sensitivity. Therefore, measurement of joint PPT could be a noninvasive diagnostic tool reflecting increased bone metabolism assessed by TPBS as a sign of bone pathophysiology.     

Alterations in endogenous pain modulation in endurance athletes: An experimental study using quantitative sensory testing and the cold-pressor task

There is evidence for long-term alterations in pain tolerance among athletes compared with normally active controls. However, scientific data on pain thresholds in this population are inconsistent, and the underlying mechanisms for the differences remain unclear. Therefore, we assessed differences and similarities in pain perception and conditioned pain modulation (CPM) at rest in endurance athletes and normally active controls.     

Persistent pain in postmastectomy patients: Comparison of psychophysical,medical, surgical,and psychosocial characteristics between patients with and without pain

Persistent postmastectomy pain (PPMP) is a major individual and public health problem. Increasingly, psychosocial factors such as anxiety and catastrophizing are being revealed as crucial contributors to individual differences in pain processing and outcomes. Furthermore, differences in patients’ responses to standardized quantitative sensory testing (QST) may aid in the discernment of who is at risk for acute and chronic pain after surgery. However, characterization of the variables that differentiate those with PPMP from those whose acute postoperative pain resolves is currently incomplete. The purpose of this study was to investigate important surgical, treatment-related, demographic, psychophysical, and psychosocial factors associated with PPMP by comparing PPMP cases with PPMP-free controls. Pain was assessed using the breast cancer pain questionnaire to determine the presence and extent of PPMP. Psychosocial and demographic information were gathered via phone interview, and women underwent a QST session. Consistent with most prior research, surgical and disease-related variables did not differ significantly between cases and controls. Furthermore, treatment with radiation, chemotherapy, or hormone therapy was also not more common among those with PPMP. In contrast, women with PPMP did show elevated levels of distress-related psychosocial factors such as anxiety, depression, catastrophizing, and somatization. Finally, QST in nonsurgical body areas revealed increased sensitivity to mechanical stimulation among PPMP cases, while thermal pain responses were not different between the groups. These findings suggest that an individual’s psychophysical and psychosocial profile may be more strongly related to PPMP than their surgical treatment.     

Deep pain thresholds in the distal limbs of healthy human subjects.

Pressure pain thresholds (PPTs) in distal limbs have been under-investigated despite their potential clinical importance. Therefore, we compared PPTs over nail bed, bony prominences, and muscle in distal parts of upper and lower limbs. We investigated 12 healthy subjects using three handheld devices: a spring-loaded, analogue pressure threshold meter (PTM) with two operating ranges, and an electronic Algometer. PPTs were determined with three series of ascending stimulus intensities with a ramp of about 50 kPa/s. PPTs were normally distributed in logarithmic space. PPTs over different tissues varied significantly (ANOVA, p<0.001): mean thresholds and 95% confidence intervals were 615 kPa (266-1424 kPa) over the nail bed, 581 kPa (271-1245 kPa) over bony prominences, and 520 kPa (246-1100 kPa) over muscles. PPTs on the foot were higher than on the hand (ANOVA, p<0.01), except over muscles. PPTs were significantly lower with the Algometer than with PTMs (ANOVA, p<0.01); again these differences were least when testing over muscle. There was no significant right-left difference (ANOVA, p=0.33). In spite of considerable variability across subjects, reproducibility within subjects was high (correlation coefficients>0.90). For within-subject comparisons, threshold elevations beyond 33-43% would be abnormal (95% confidence intervals), whereas only deviations from the group mean by at least a factor of two would be abnormal with respect to absolute normative values. PPTs over distal muscles were comparable to published values on proximal limb and trunk muscles. These findings suggest that pressure pain testing over distal muscles may be a sensitive test for deep pain sensitivity and that the simple and less expensive devices are sufficient for testing this tissue type. Intra-individual site-to-site comparisons will be more sensitive than absolute normative values.     

Characteristics of referred muscle pain to the head from active trigger points in women with myofascial temporomandibular pain and fibromyalgia syndrome

Our aim was to compare the differences in the prevalence and the anatomical localization of referred pain areas of active trigger points (TrPs) between women with myofascial temporomandibular disorder (TMD) or fibromyalgia (FMS). Twenty women (age 46 ± 8 years) with TMD and 20 (age 48 ± 6 years) with FMS were recruited from specialized clinic. Bilateral temporalis, masseter, sternocleidomastoid, upper trapezius, and suboccipital muscles were examined for TrPs. TrPs were identified by palpation and considered active when the pain reproduced familiar pain symptom experienced by the patient. The referred pain areas were drawn on anatomical maps, digitalized and also measured. A new analysis technique based on a center of gravity (COG) method was used to quantitative estimate of the localization of the TrP referred pain areas. Women with FMS exhibited larger areas of usual pain symptoms than women with myofascial TMD (P < 0.001). The COG coordinates of the usual pain on the frontal and posterior pain maps were located more superior in TMD than in FMS. The number of active TrPs was significantly higher in TMD (mean ± SD 6 ± 1) than in FMS (4 ± 1) (P = 0.002). Women with TMD exhibited more active TrPs in the temporalis and masseter muscles than FMS (P < 0.01). Women with FMS had larger referred pain areas than those with TMD for sternocleidomastoid and suboccipital muscles (P < 0.001). Significant differences within COG coordinates of TrP referred pain areas were found in TMD, the referred pain was more pronounced in the orofacial region, whereas the referred pain in FMS was more pronounced in the cervical spine. This study showed that the referred pain elicited from active TrPs shared similar patterns as usual pain symptoms in women with TMD or FMS, but that distinct differences in TrP prevalence and location of the referred pain areas could be observed. Differences in location of referred pain areas may help clinicians to determine the most relevant TrPs for each pain syndrome in spite of overlaps in pain areas.     

Fear of pain, not pain catastrophizing, predicts acute pain intensity, but neither factor predicts tolerance or blood pressure reactivity: an experimental investigation in pain-free individuals.

Previous studies of the Fear-Avoidance Model of Exaggerated Pain Perception have commonly included patients with chronic low back pain, making it difficult to determine which psychological factors led to the development of an "exaggerated pain perception". This study investigated the validity of the Fear-Avoidance Model of Exaggerated Pain Perception by considering the influence of fear of pain and pain catastrophizing on acute pain perception, after considering sex and anxiety. Thirty-two males and 34 females completed the State-Trait Anxiety Inventory, the Fear of Pain Questionnaire, and the Coping Strategies Questionnaire. Subjects underwent a cold pressor procedure and tolerance, pain intensity, and blood pressure reactivity were measured. Sex, anxiety, fear of pain, and pain catastrophizing were simultaneously entered into separate multiple regression models to predict different components of pain perception. Tolerance was not predicted by fear of pain, pain catastrophizing, or anxiety. Pain intensity at threshold and tolerance were significantly predicted by fear of pain, only. Blood pressure reactivity to pain was significantly predicted by anxiety, only. These results suggest that fear of pain may have a stronger influence on acute pain intensity when compared to pain catastrophizing, while neither of the factors predicted tolerance or blood pressure reactivity.     

Heterotopic noxious conditioning stimulation (HNCS) reduced the intensity of spontaneous pain, but not of allodynia in painful peripheral neuropathy.

In 15 patients with painful peripheral neuropathy and dynamic mechanical allodynia, the influence of spontaneous ongoing neuropathic pain on pain sensitivity in a remote pain-free area was examined, as was the influence of ischemia-induced heterotopic noxious conditioning stimulation (HNCS) on the intensity of ongoing pain and brush-evoked allodynia. In addition, the modulating effect of HNCS on pain sensitivity in a pain-free area was investigated. Pain thresholds to pressure and heat as well as the sensitivity to suprathreshold pressure- and heat pain were assessed in the pain-free area. Dynamic mechanical allodynia was induced by a recently developed semi-quantitative brushing technique and the patients continuously rated the intensity of the allodynia using a computerized visual analogue scale (VAS). The total brush-evoked pain intensity was calculated as the area under the VAS curve. At baseline, no significant difference in pain sensitivity was found between patients and their healthy controls in the pain-free area, indicating a lack of activation of pain modulatory systems from the spontaneous pain. Compared to baseline, the patients rated the ongoing neuropathic pain intensity significantly lower during the HNCS-procedure (p<0.05). In contrast, there was no influence from HNCS on the total brush-evoked pain intensity. In the pain-free area higher pressure pain thresholds were demonstrated during conditioning stimulation in patients and controls alike (p<0.01). In controls only, a significantly higher heat pain threshold was found during the HNCS-procedure (p<0.01). The main finding of the present study was that HNCS altered differentially spontaneous and brush-provoked pain in patients with painful peripheral neuropathy.