Predictors of clinical pain intensity in patients with fibromyalgia syndrome

Temporal Summation of the Thermal Grill Illusion is Comparable to That Observed Following Noxious Heat

The thermal grill illusion (TGI) describes a peculiar or even painful percept caused by non-noxious, interlaced warm and cold stimuli. It involves the glutamatergic system and is affected in putatively nociplastic syndromes such as fibromyalgia. The glutamatergic system is also involved in wind-up, that is, the increased activation of spinal neurons following repeated noxious stimulation leading to a temporal summation of perceived stimulus intensity. Here we combined both stimulation methods to further investigate whether non-noxious stimuli as employed in the TGI can lead to a similar summation of perceived stimulus intensity. In an experiment using a full crossover within-subjects design, 35 healthy volunteers received repeated stimuli, either in a thermal grill configuration or simply noxious heat. Both modalities were presented as sequences of 1 lead-in contact, followed by 11 consecutive contacts (each between 1.5 and 3 seconds), with either fast repetition ("wind-up" condition), or 2 slow-repeating control conditions. The main analyses concerned the relative pre-to-post sequence changes to quantify putatively wind-up-related effects. Pain ratings and skin conductance level (SCL) increased more strongly in "wind-up" than in control conditions. Interestingly, wind-up-related effects were of the same magnitude in TGI as compared to the pain control modality. Further, contact-by-contact SCL tracked how the effect emerged over time. These results indicate that although TGI does not involve noxious stimuli it is amenable to temporal summation and wind-up-like processes. Since both phenomena involve the glutamatergic system, the combination of wind-up with the TGI could yield a promising tool for the investigation of chronic pain conditions. PERSPECTIVE: Using thermal stimuli in an experimental protocol to combine 1) the TGI (painful or peculiar percept from simultaneous cold/warm stimulation) and 2) wind-up (increase in stimulus intensity after repeated exposure) holds promise to investigate pain and thermoceptive mechanisms, and chronic pain conditions.

Short-term plasticity in the spinal nociceptive system

ABSTRACT

Somatosensory information is delivered to neuronal networks of the dorsal horn (DH) of the spinal cord by the axons of primary afferent neurons that encode the intensity of peripheral sensory stimuli under the form of a code based on the frequency of action potential firing. The efficient processing of these messages within the DH involves frequency-tuned synapses, a phenomenon linked to their ability to display activity-dependent forms of short-term plasticity (STP). By affecting differently excitatory and inhibitory synaptic transmissions, these STP properties allow a powerful gain control in DH neuronal networks that may be critical for the integration of nociceptive messages before they are forwarded to the brain, where they may be ultimately interpreted as pain. Moreover, these STPs can be finely modulated by endogenous signaling molecules, such as neurosteroids, adenosine, or GABA. The STP properties of DH inhibitory synapses might also, at least in part, participate in the pain-relieving effect of nonpharmacological analgesic procedures, such as transcutaneous electrical nerve stimulation, electroacupuncture, or spinal cord stimulation. The properties of target-specific STP at inhibitory DH synapses and their possible contribution to electrical stimulation-induced reduction of hyperalgesic and allodynic states in chronic pain will be reviewed and discussed.

Chronic Pain in Multiple Sclerosis Patients: Utility of Sensory Quantitative Testing in Patients with Fibromyalgia Comorbidity

BACKGROUND

Lower thermal and discomfort thresholds may predispose multiple sclerosis (MS) patients to chronic pain, but a possible effect of fibromyalgia (FM) comorbidity has never been investigated. Aims were to investigate the thermal and discomfort thresholds in the evaluation of pain intensity between MS patients with FM (PFM+) and MS patients with pain not associated to FM (PFM-).

METHODS

One hundred thirty three MS patients were investigated for chronic pain. FM was assessed according to the 1990 ACR diagnostic criteria. An algometer was used to measure the thresholds in the patients and 60 matched healthy subjects.

RESULTS

Chronic pain was present in 88 (66.2%) patients; 12 (13.6%) had neuropathic pain, 22 (17.3%) were PFM+ and 65 (48.9%) PFM-. PFM+ were predominantly female (p = 0.03) and had a greater EDSS (p = 0.01) than NoP; no other significant differences emerged than PFM-. The thresholds were lower in MS patients than controls (p < 0.01), mainly in the PFM+. FM severity influenced the thermal threshold (p < 0.001), while the female gender influenced the discomfort threshold (p < 0.001).

CONCLUSION

Thermal and discomfort thresholds were lower in patients than controls and were the lowest in PFM+. Their more severely impaired thermal threshold supports a neurophysiological basis of such association.

Test-retest reliability of pain-related brain activity in healthy controls undergoing experimental thermal pain

Although functional magnetic resonance imaging (fMRI) has been proposed as a method to elucidate pain-related biomarkers, little information exists related to psychometric properties of fMRI findings. This knowledge is essential for potential translation of this technology to clinical settings. The purpose of this study was to assess the test-retest reliability of pain-related brain activity and how it compares to the reliability of self-report. Twenty-two healthy controls (mean age = 22.6 years, standard deviation = 2.9) underwent 3 runs of an fMRI paradigm that used thermal stimuli to elicit experimental pain. Functional MRI summary statistics related to brain activity during thermal stimulation periods were extracted from bilateral anterior cingulate cortices and anterior insula. Intraclass correlations (ICCs) were conducted on these summary statistics and generally showed "good" test-retest reliability in all regions of interest (ICC range = .32-.88; mean = .71); however, these results did not surpass ICC values from pain ratings, which fell within the "excellent" range (ICC range = .93-.96; mean = .94). Findings suggest that fMRI is a valuable tool for measuring pain mechanisms but did not show an adequate level of test-retest reliability for fMRI to potentially act as a surrogate for individuals' self-report of pain.

PERSPECTIVE

This study is one of the first reports to demonstrate the test-retest reliability of fMRI findings related to pain processing and provides a comparison to the reliability of subjective reports of pain. This information is essential for determining whether fMRI technology should be potentially translated for clinical use.

The Relationship between Mechanical Hyperalgesia Assessed by Manual Tender Point Examination and Disease Severity in Patients with Chronic Widespread Pain: A Cross-Sectional Study

The clinical utility of tender point (TP) examination in patients reporting chronic widespread pain (CWP) is the subject of contemporary debate. The objective of this study was to assess the relationship between mechanical hyperalgesia assessed by manual TP examination and clinical disease severity. 271 women with CWP were recruited from a clinical setting. Data collection included patient-reported symptoms, health-related quality of life variables, and observation-based measures of functional ability, muscle strength, 6-minute walk, and pressure pain thresholds measured by cuff algometry. TP examination was conducted according to ACR-guidelines. Relationships between disease variables and TP count (TPC) were analyzed with logistic regression in a continuum model, allowing the TPC to depend on the included disease variables and two regression models carried out for a TPC threshold level, varying between 1 and 17. The threshold analyses indicated a TPC threshold at 8, above which a large number of disease variables became consistently significant explanatory factors, whereas none of the disease variables reached a significance level in the continuum model. These results support the premise that the presence of mechanical hyperalgesia influences symptomatology in CWP and that the severity of clinical expression is related to a threshold of TPs, rather than being part of a continuum.

Slow temporal summation of pain for assessment of central pain sensitivity and clinical pain of fibromyalgia patients

BACKGROUND

In healthy individuals slow temporal summation of pain or wind-up (WU) can be evoked by repetitive heat-pulses at frequencies of ≥.33 Hz. Previous WU studies have used various stimulus frequencies and intensities to characterize central sensitization of human subjects including fibromyalgia (FM) patients. However, many trials demonstrated considerable WU-variability including zero WU or even wind-down (WD) at stimulus intensities sufficient for activating C-nociceptors. Additionally, few WU-protocols have controlled for contributions of individual pain sensitivity to WU-magnitude, which is critical for WU-comparisons. We hypothesized that integration of 3 different WU-trains into a single WU-response function (WU-RF) would not only control for individuals' pain sensitivity but also better characterize their central pain responding including WU and WD.

METHODS

33 normal controls (NC) and 38 FM patients participated in a study of heat-WU. We systematically varied stimulus intensities of.4 Hz heat-pulse trains applied to the hands. Pain summation was calculated as difference scores of 1st and 5th heat-pulse ratings. WU-difference (WU-Δ) scores related to 3 heat-pulse trains (44°C, 46°C, 48°C) were integrated into WU-response functions whose slopes were used to assess group differences in central pain sensitivity. WU-aftersensations (WU-AS) at 15 s and 30 s were used to predict clinical FM pain intensity.

RESULTS

WU-Δ scores linearly accelerated with increasing stimulus intensity (p<.001) in both groups of subjects (FM>NC) from WD to WU. Slope of WU-RF, which is representative of central pain sensitivity, was significantly steeper in FM patients than NC (p<.003). WU-AS predicted clinical FM pain intensity (Pearson's r = .4; p<.04).

CONCLUSIONS

Compared to single WU series, WU-RFs integrate individuals' pain sensitivity as well as WU and WD. Slope of WU-RFs was significantly different between FM patients and NC. Therefore WU-RF may be useful for assessing central sensitization of chronic pain patients in research and clinical practice.

Transcutaneous electrical nerve stimulation reduces pain, fatigue and hyperalgesia while restoring central inhibition in primary fibromyalgia

Because transcutaneous electrical nerve stimulation (TENS) works by reducing central excitability and activating central inhibition pathways, we tested the hypothesis that TENS would reduce pain and fatigue and improve function and hyperalgesia in people with fibromyalgia who have enhanced central excitability and reduced inhibition. The current study used a double-blinded randomized, placebo-controlled cross-over design to test the effects of a single treatment of TENS with people with fibromyalgia. Three treatments were assessed in random order: active TENS, placebo TENS and no TENS. The following measures were assessed before and after each TENS treatment: pain and fatigue at rest and in movement; pressure pain thresholds, 6-m walk test, range of motion; 5-time sit-to-stand test, and single-leg stance. Conditioned pain modulation was completed at the end of testing. There was a significant decrease in pain and fatigue with movement for active TENS compared to placebo and no TENS. Pressure pain thresholds increased at the site of TENS (spine) and outside the site of TENS (leg) when compared to placebo TENS or no TENS. During active TENS, conditioned pain modulation was significantly stronger compared to placebo TENS and no TENS. No changes in functional tasks were observed with TENS. Thus, the current study suggests TENS has short-term efficacy in relieving symptoms of fibromyalgia while the stimulator is active. Future clinical trials should examine the effects of repeated daily delivery of TENS, similar to the way in which TENS is used clinically on pain, fatigue, function, and quality of life in individuals with fibromyalgia.

Pain measurement and brain activity: will neuroimages replace pain ratings?

Arguments made for the advantages of replacing pain ratings with brain-imaging data include assumptions that pain ratings are less reliable and objective and that brain image data would greatly benefit the measurement of treatment efficacy. None of these assumptions are supported by available evidence. Self-report of pain is predictable and does not necessarily reflect unreliability or error. Because pain is defined as an experience, magnitudes of its dimensions can be estimated by well-established methods, including those used to validate brain imaging of pain. Brain imaging helps to study pain mechanisms and might be used as proxy measures of pain in persons unable to provide verbal reports. Yet eliminating pain ratings or replacing them with neuroimaging data is misguided because brain images only help explain pain if they are used in conjunction with self-report. There is no objective readout mechanism of pain (pain thermometer) that is unaffected by psychological factors. Benefits from including neuroimaging data might include increased understanding of underlying neural mechanisms of treatment efficacy, discovery of new treatment vectors, and support of conclusions derived from self-report. However, neither brain imaging nor self-report data are privileged over the other. The assumption that treatment efficacy is hampered by self-report has not been shown; there is a plethora of treatment studies showing that self-report is sensitive to treatment. Dismissal of patients' self-reports (pain ratings) by brain-imaging data is potentially harmful. The aim of replacing self-report with brain-imaging data is misguided and has no scientific or philosophical foundation.

PERSPECTIVE

Although brain imaging may offer considerable insight into the neural mechanisms of pain, including relevant causes and correlations, brain images cannot and should not replace self-report. Only the latter assesses the experience of pain, which is not identical to neural activity. Brain imaging may help to explain pain, but replacing self-report with brain-imaging data would be philosophically and scientifically misguided and potentially harmful to pain patients.

Pain-related diseases and sleep disorders

Pain and sleep share mutual relations under the influence of cognitive and neuroendocrine changes. Sleep is an important homeostatic feature and, when impaired, contributes to the development or worsening of pain-related diseases. The aim of the present review is to provide a panoramic view for the generalist physician on sleep disorders that occur in pain-related diseases within the field of Internal Medicine, such as rheumatic diseases, acute coronary syndrome, digestive diseases, cancer, and headache.

Cognitive-affective assets and vulnerabilities: two factors influencing adaptation to fibromyalgia

This study set to explore whether variables related to cognitive-affective assets would complement measures of psychological vulnerability for the prediction of physical functioning and pain tolerance in 138 women with Fibromyalgia Syndrome (FMS). Depression, anxiety, stress response and negative affect were defined a priori as measures of vulnerability, while pain self-efficacy, internality and positive affect were identified as assets. Confirmatory factor analyses supported the validity of the hypothesised two-factor structure in FMS. A structural equation model (SEM) revealed that the two factors were associated with different outcomes in FMS as predictors. Pain and associated symptoms appeared related to psychological vulnerabilities in FMS patients, whereas physical functioning and tolerance for pain were better predicted by assets. These results are discussed with reference to current theoretical models concerning the role of psychological factors in FMS, and intervention methods designed to improve quality of life and reduce pain in FMS patients.

Further strategies for treating fibromyalgia: the role of serotonin and norepinephrine reuptake inhibitors

Fibromyalgia and associated conditions such as irritable bowel syndrome and temporomandibular disorder involve dysfunctions in central sensitization and pain modulation. Central nervous system dysfunction may also contribute to other symptoms characteristic of fibromyalgia, such as fatigue and sleep disturbance. Two key neurotransmitters in the pain modulation pathway are serotonin and norepinephrine. Preclinical studies using animal models of chronic pain have shown that pharmacologic agents that combine serotonergic and noradrenergic reuptake inhibition, thus augmenting the function of these neurotransmitters, have stronger analgesic effects than agents that inhibit reuptake of either neurotransmitter alone. Although tricyclic antidepressants (TCAs) inhibit reuptake of both serotonin and norepinephrine and have shown efficacy for the treatment of fibromyalgia, long-term use of these drugs is limited owing to poor tolerability. Unlike TCAs, the newer dual reuptake inhibitors of serotonin and norepinephrine, such as the drugs approved by the US Food and Drug Administration (FDA) for fibromyalgia, milnacipran and duloxetine, do not possess significant affinity for other neurotransmitter systems, resulting in diminished side effects and enhanced tolerability. Both duloxetine and milnacipran have shown efficacy in clinical trials by improving pain and other symptoms associated with fibromyalgia. Both compounds inhibit the serotonin and norepinephrine transporters; however, there is a difference in their affinities and selectivity for these transporters. Although duloxetine has affinity for both receptors, it is somewhat more selective for the serotonin transporter. In contrast, milnacipran is somewhat more selective for norepinephrine than serotonin reuptake inhibition. Pharmacologic agents that specifically target serotonin and norepinephrine reuptake may prove to be valuable tools in the treatment of fibromyalgia.

[Relationship between COMT gene genotypes and severity of fibromyalgia]

BACKGROUND AND AIM

To determine the possible relationship between Val158Met genotypes of the COMT gene and the severity of fibromyalgia (FM) syndrome.

PATIENTS AND METHODS

The study included 110 patients aged between 45 and 55 years old diagnosed with FM (ACR, 1990) and 110 samples from control subjects with no pain and no abnormal fatigue (National DNA Bank, Spain). To measure the severity of fibromyalgia, the Fibromyalgia Impact Questionnaire (FIQ) was used. Severe FM was defined as an FIQ of ≥ 70 and was found in 35.5% of the patients. Polymorphisms were analyzed using standard polymerase chain reaction techniques. All the groups met the Hardy-Weinberg equilibrium.

RESULTS

The frequency of the Met/Met genotype was lower in controls (20.9%) than in patients (34.5%), whereas that of the Val/Val genotype was higher in controls (30.9%) than in patients (20.0%), with significant differences (p=0.048). The mean FIQ values were higher in the Met/Met genotypes (71.67) and Val/Met genotypes (68.27) and were lower in the Val/Val genotype (58.93). Tukey's multiple comparison test indicated that FIQ values presented significant differences when Met/Met/Val/Val (Tukey, p<0.001) and Val/Val/Val/Met (Tukey, p=0.003) were compared.

CONCLUSIONS

Our results appear to indicate that the Met/Met genotype is associated with greater severity of FM symptoms.

Pain intensity and severe pain in young immigrant patients with long-standing back pain

The aim of this study was to explore if self-rated pain intensity and severe pain differed significantly between immigrants from different regions, and if other socio-economic, or clinical, characteristics could predict severe pain. A total of 129 men and 217 women at a primary health centre in Stockholm, Sweden, 27-45 years, on long-term sick leave, were recruited in consecutive order and grouped into a Turkish (n = 122), Southern European (n = 52), Middle East (n = 69) and one Mixed (n = 173) group of immigrants. All were employed in service jobs. Somatic status, depression and level of psychosocial stressors, including pain anxiety, were established by standardized procedures. All reported long-standing disabling back pain. Patients rated intensity of pain "right now" on a 0-100 mm visual analogue scale (VAS) as a last part of the consultation with two doctors. Severe pain was defined as VAS 75-100. Median values (md) with inter-quartile ranges (IQR) were calculated for interval and ordinal data. Non-parametric statistics were used to calculate significant differences between groups. Crude and age-standardized odds ratios (OR) with 95% confidence intervals (95% CI) as rating severe pain were calculated by binary and forward conditional logistic regression. Men and women were analyzed separately. Women had more tender points, (P < 0.001), and reported pain anxiety more often (P < 0.01). Frequency of depression did not differ between the immigrant groups. The VAS-values varied, but not significantly, between the immigrant groups of men and women. Men had lower VAS values than women (md 50, IQR 36-69 vs. md 72, IQR 51-85), (P < 0.001). Women had a three-fold risk to rate severe pain (OR 2.9, 95% CI 1.8-4.7). By sex, no immigrant group had significantly elevated OR to rate severe pain. Being 40-45 year old doubled the OR as rating severe pain. Men with depression, or little education, had high risks as rating severe pain (age-standardized ORs 4.1; 95% CI 1.7-10.0 and 2.7; 95% CI 1.1-6.8, respectively), and so had depressed women (age-standardized OR 1.9; 95% CI 1.1-3.4). Women with pain anxiety had a doubled, not statistically significant, elevated risk (age-standardized OR 2.0, 95% CI 0.95-4.3). The groups did not differ significantly in pain intensity or severe pain. Severe pain was predicted by depressed mood and probably linked to gender, age and sick roles.

Imaging pain of fibromyalgia

Brain imaging studies have provided objective evidence of abnormal central regulation of pain in fibromyalgia (FM). Resting brain blood flow studies have reported mixed findings for several brain regions, whereas decreased thalamic blood flow has been noted by several investigators. Studies examining the function of the nociceptive system in FM have reported augmented brain responses to both painful and non-painful stimuli that may be influenced by psychologic dispositions such as depressed mood and catastrophizing. Treatment approaches are beginning to demonstrate the potential for brain imaging to improve our understanding of pain-alleviating mechanisms. Data from other chronic conditions suggest that idiopathic pain may be maintained by similar central abnormalities as in FM, whereas chronic pain conditions with a known nociceptive source may not be. Future neuroimaging research in FM is clearly warranted and should continue to improve our understanding of factors involved in pain maintenance and symptom exacerbation.

Myofascial pain syndromes and their evaluation

Myofascial pain refers to a specific form of soft-tissue rheumatism that results from irritable foci (trigger points) within skeletal muscles and their ligamentous junctions. It must be distinguished from bursitis, tendonitis, hypermobility syndromes, fibromyalgia and fasciitis. On the other hand it often exists as part of a clinical complex that includes these other soft-tissue conditions, i.e., it is not a diagnosis of exclusion. The clinical science of trigger points can be traced to the pioneering work of Kellgren in the 1930s, with his mapping of myotomal referral patterns of pain resulting from the injection of hypertonic saline into muscle and ligaments. Most muscles have characteristic myotomal patterns of referred pain; this feature forms the basis of the clinical recognition of myofascial trigger points in the form of a tender locus within a taut band of muscle which restricts the full range of motion and refers pain centrifugally when stimulated. Although myofascial pain syndromes have been described in the medical literature for about the last 100 years, it is only recently that scientific studies have revealed objective abnormalities.