Electrical low-frequency stimulation (LFS) inhibits pain perception and nociceptive processing as shown by psychophysical and electrophysiological means (long-term depression, LTD). Information regarding central mechanisms involved in LTD induction and maintenance are still missing. This study hypothesizes that electrical LFS induces changes in activation pattern of pain-related brain areas. Thirty-two electrophysiological and psychophysical experiments were performed in 16 healthy volunteers. Painful electrical test stimulation (0.125Hz, 60 pulses) and conditioning LFS (1Hz, 1200 pulses) were applied by a concentric electrode to the right hand. Test stimulation series were performed before (Pre) and after LFS (Post) or no stimulation period (Control). Volunteers rated pain perception according to a verbal rating scale (0-100). Somatosensory evoked cortical potentials were recorded with 64-channel electroencephalography. Individual dipole source modeling using CURRY software (Compumedics, Hamburg, Germany) yielded information about dipole location and strength. The strongest decrease in LFS-induced pain perception was shown after LFS (p<0.01). Topographic distribution of cortical potentials revealed reproducible negative (N1, N2) and positive (P2) components. Dipole magnitude analysis showed a significant difference between Post LFS and Post Control for P2 (p<0.01). P2 dipole location analysis yielded a significant posterior (p<0.05) shift following LTD induction. Thus, data reveal central changes of pain processing after LTD induction. These experiments may help judging the potency of LTD as model for electrostimulation in future analgesic therapy.
PMID: 21968391 [PubMed - as supplied by publisher]
Ten year course of low back pain in an adult population-based cohort – The Doetinchem Cohort Study.
Eur J Pain. 2011 Oct;15(9):993-8
Authors: van Oostrom SH, Monique Verschuren WM, de Vet HC, Picavet HS
Abstract
BACKGROUND: The long-term course of long-standing low back pain is largely unknown since long-term data are scarce.
OBJECTIVE: We examined the course of self-reported low back pain in the prospective population-based Doetinchem cohort over a period of 10years.
METHODS: Between 1993 and 2007, around 5700 randomly selected men and women in four age groups of originally 20-29, 30-39, 40-49, 50-59years were measured three times. Logistic regression analysis was used to study the association of sociodemographic (gender, age, education, work status) and lifestyle characteristics (BMI, smoking, physical activity) with persistent and new episodes of long-standing low back pain.
RESULTS: The prevalence of long-standing low back pain is quite stable over a 10year period, approximately 20% on population level. On individual level, around 30% of the population was completely free of low back pain during the entire period, 6% can be characterized as persistent back pain sufferers. Individuals with persistent and a varying pattern have a more unhealthy lifestyle (BMI and smoking) than those without low back pain. Age, smoking, obesity and not having a paid job are associated with 10-year persistent back pain in the general population, whereas age and not having a paid job are associated in those with long-lasting back pain at baseline. New episodes of long-standing back pain are relatively frequent among women and smokers.
CONCLUSIONS: Low back pain in the population is characterized as very dynamic which challenges epidemiological studies highly. Long-term information on the course of back pain is needed to define severe subgroups.
Specialized multimodal outpatient treatment for children with chronic pain: Treatment pathways and long-term outcome.
Eur J Pain. 2011 Oct;15(9):976-84
Authors: Hechler T, Martin A, Blankenburg M, Schroeder S, Kosfelder J, Hölscher L, Denecke H, Zernikow B
Abstract
Objective: Despite the increased recognition of paediatric chronic pain, centres for providing appropriate treatment are scarce, and much remains unknown about optimal treatment approaches. The purpose of this study was to investigate effectiveness of multimodal outpatient treatment (MOT) through the examination of treatment pathways and long-term outcomes. Methods: Within an observational longitudinal study, 275 children (4-18years) formed the study group and received MOT. Over a 12-month period, we followed the progress of the study group to identify how many children completed treatment, how many continued treatment and how many were stepped-up to more intensive treatment. To investigate significant and clinically relevant changes in primary and secondary outcomes the study group was assessed at three consecutive treatment sessions (initial session, 3-, 6-month visit) and 12months following the initial session. Results: Analysis of treatment pathways showed that 1/3 of the children did not attend the prescribed second and third visit to the clinic. Cessation of treatment correlated with significant improvement. Only a small number of children were still in treatment at 12-month follow-up (12%) or needed more intensive treatment (11%). At 12-month follow-up, almost 70% of children in the study group were able to attend school regularly. Pain intensity, pain-related disability and inappropriate coping strategies were significantly reduced at 3-month visit and remained stable at the subsequent time points. Conclusions: MOT appears to be beneficial for children with chronic pain. A short intensive intervention (comprising of a total of 2.5-h) can lead to substantial improvements even for severely affected children.
Gender effects in pain detection: Speed and accuracy in decoding female and male pain expressions.
Eur J Pain. 2011 Oct;15(9):985.e1-985.e11
Authors: Riva P, Sacchi S, Montali L, Frigerio A
Abstract
The ability to detect facial expressions of pain is crucial in eliciting prosocial behaviors towards the individual experiencing pain. Previous studies have shown that the sufferers’ gender can affect the observers’ explicit judgment of the pain face, thus suggesting its possible influence on pain decoding. The present study investigates whether the sufferer’s gender affects the observer’s reflexive or implicit detection of facial expression of pain. More specifically, we used implicit measures to test whether observers detect pained expression more quickly or accurately on male or female faces. In three experimental studies, we devised a set of stimuli using computer-generated faces. In Experiment 1, prototypical female and male avatars with different facial expressions (pain, anger, disgust, and neutral) were displayed, while subjects’ (N=34) accuracy and speed at identifying the expressions were recorded. In Experiment 2, participants (N=56) watched videos of the avatars displaying dynamic expressions and had to quickly and accurately identify each expression. In Experiment 3, participants (N=38) were shown an androgynous avatar face showing different expressions and were asked to identify the face as either female or male. Overall, we found that the target’s gender affected the observer’s reflexive decoding of the facial expression of pain. Specifically, the results showed that participants, regardless of their gender, were slower and less accurate in recognizing pain expressions (but not other expressions) on female faces. Furthermore, androgynous faces displaying pained expressions were more likely to be categorized as male than female. Several potential explanations are discussed.
Understanding fear of pain in chronic pain: Interoceptive fear conditioning as a novel approach.
Eur J Pain. 2011 Oct;15(9):889-94
Authors: De Peuter S, Van Diest I, Vansteenwegen D, Van den Bergh O, Vlaeyen JW
Abstract
The current review deals with interoceptive conditioning as a viable mechanism maintaining fear of pain: The available literature suggests that interoceptive – i.e., internal bodily – sensations may become predictors of pain and will subsequently elicit fear of pain. After a short overview of interoceptive (fear) conditioning and its role in the maintenance of panic disorder, the existing literature on conditioning in the field of pain and fear of pain is reviewed. Next, the authors propose an interoceptive fear conditioning model of fear of pain, suggesting that bodily sensations can function as predictors of pain and as conditioned stimuli become endowed with the capacity to elicit an (anticipatory) fear response. The review concludes with a number of theoretical and clinical considerations, introducing interoceptive exposure as a potentially effective treatment for fear of pain.
The association between psychological factors and the development of complex regional pain syndrome type 1 (CRPS1) – A prospective multicenter study.
Eur J Pain. 2011 Oct;15(9):971-5
Authors: Beerthuizen A, Stronks DL, Huygen FJ, Passchier J, Klein J, Spijker AV
Abstract
The objective of this study was to investigate the association between psychological factors and complex regional pain syndrome type 1 (CRPS1). A prospective multicenter cohort study was performed involving the emergency room of three hospitals, and patients age 18years or older, with a single fracture, were included in the study. At baseline (T0), participants completed a questionnaire covering demographic, psychological (Symptom Checklist-90), and medical variables. At plaster removal (T1) and at T2, the participants completed a questionnaire addressing symptoms of CRPS1. Psychological factors that were analysed were agoraphobia, depression, somatization, insufficiency, (interpersonal) sensitivity, insomnia, and life events. In total, 596 consecutive patients were included in the study, and 7.0% were diagnosed with CRPS1. None of the psychological factors predicted the development of CRPS1. The scores on the Symptom Checklist-90 subscales fell into the range of the general population and were, in most cases, average or below average when compared with those of pain patients or psychiatric patients. No empirical evidence supports a diagnosis of CRPS1 patients as psychologically different, and the current results indicate that there is no association between psychological factors and CRPS1.
Absence of long-term analgesic effect from a short-term S-ketamine infusion on fibromyalgia pain: A randomized, prospective, double blind, active placebo-controlled trial.
Eur J Pain. 2011 Oct;15(9):942-9
Authors: Noppers I, Niesters M, Swartjes M, Bauer M, Aarts L, Geleijnse N, Mooren R, Dahan A, Sarton E
Abstract
To assess the analgesic efficacy of the N-methyl-D-aspartate receptor antagonist S(+)-ketamine on fibromyalgia pain, the authors performed a randomized double blind, active placebo-controlled trial. Twenty-four fibromyalgia patients were randomized to receive a 30-min intravenous infusion with S(+)-ketamine (total dose 0.5mg/kg, n=12) or the active placebo, midazolam (5mg, n=12). Visual Analogue Pain Scores (VAS) and ketamine plasma samples were obtained for 2.5-h following termination of treatment; pain scores derived from the fibromyalgia impact questionnaire (FIQ) were collected weekly during an 8-week follow-up. Fifteen min after termination of infusion the number of patients showing a reduction in pain scores >50% was 8 vs. 3 (P<0.05), at t=180min 6 vs. 2 (ns), at the end of week-1 2 vs. 0 (ns) and at end of week-8 2 vs. 2 in the ketamine and midazolam groups, respectively. Ketamine effect on VAS closely followed ketamine plasma concentrations. For VAS and FIQ scores no significant differences in treatment effects were observed in the 2.5-h following infusion or during the 8-week follow-up. Side effects as measured by the Bowdle questionnaire (which scores for 13 separate psychedelic symptoms) were mild to moderate in both study groups and declined rapidly, indicating adequate blinding of treatments. Efficacy of ketamine was limited and restricted in duration to its pharmacokinetics. The authors argue that a short-term infusion of ketamine is insufficient to induce long-term analgesic effects in fibromyalgia patients.
Vector-mediated release of GABA attenuates pain-related behaviors and reduces Na(V)1.7 in DRG neurons.
Eur J Pain. 2011 Oct;15(9):913-20
Authors: Chattopadhyay M, Mata M, Fink DJ
Abstract
Pain is a common and debilitating accompaniment of neuropathy that occurs as a complication of diabetes. In the current study, we examined the effect of continuous release of gamma amino butyric acid (GABA), achieved by gene transfer of glutamic acid decarboxylase (GAD67) to dorsal root ganglia (DRG) in vivo using a non-replicating herpes simplex virus (HSV)-based vector (vG) in a rat model of painful diabetic neuropathy (PDN). Subcutaneous inoculation of vG reduced mechanical hyperalgesia, thermal hyperalgesia and cold allodynia in rats with PDN. Continuous release of GABA from vector transduced cells in vivo prevented the increase in the voltage-gated sodium channel isoform 1.7 (Na(V)1.7) protein that is characteristic of PDN. In vitro, infection of primary DRG neurons with vG prevented the increase in Na(V)1.7 resulting from exposure to hyperglycemia. The effect of vector-mediated GABA on Na(V)1.7 levels in vitro was blocked by phaclofen but not by bicuculline, a GABA(B) receptor effect that was blocked by pertussis toxin-(PTX) interference with Gα((i/o)) function. Taken in conjunction with our previous observation that continuous activation of delta opioid receptors by vector-mediated release of enkephalin also prevents the increase in Na(V)1.7 in DRG exposed to hyperglycemia in vitro or in vivo, the observations in this report suggest a novel common mechanism through which activation of G protein coupled receptors (GPCR) in DRG neurons regulate the phenotype of the primary afferent.
Abnormal facilitatory mechanisms in motor cortex of migraine with aura.
Eur J Pain. 2011 Oct;15(9):928-35
Authors: Brighina F, Cosentino G, Vigneri S, Talamanca S, Palermo A, Giglia G, Fierro B
Abstract
Experimental evidence suggests impairment of inhibitory intracortical circuits in migraine, while not much is known about activity of facilitatory intracortical circuits. In the present work we evaluated the effects of high frequency-repetitive transcranial magnetic stimulation (hf-rTMS) on the activity of facilitatory circuits of motor cortex in 18 patients affected by migraine with aura and 18 healthy subjects. Trains of 10 stimuli were applied to the motor cortex at 5-Hz frequency with recording of the EMG traces from the contralateral abductor pollicis brevis muscle (APB). Two intensities of stimulation (110% and 130% of resting motor threshold) were used in order to explore whether motor cortex excitability was differently modulated. Twelve patients underwent hf-rTMS both before and during prophylactic treatment with levetiracetam. Results showed that rTMS delivered at 110% intensity of stimulation at rest had a facilitatory effect on MEP size in untreated patients, while left MEP unchanged in controls. Conversely, when rTMS was applied at 130%, we observed MEP potentiation in healthy subjects and paradoxical MEP inhibition in migraineurs. In treated patients, levetiracetam inhibited MEP size at both 110% and 130% intensity of stimulation. Our findings reveal an opposite response of migraine motor cortex to 5-Hz rTMS when it is delivered at different stimulation intensities, providing evidence of both hyper-responsivity and self-limiting hyperexcitability capacity, in line with studies supporting the concept that under conditions of cortical hyperexcitability inhibitory mechanisms of homeostatic plasticity could be activated.
On the contextual nature of sex-related biases in pain judgments: The effects of pain duration, patient’s distress and judge’s sex.
Eur J Pain. 2011 Oct;15(9):950-7
Authors: Bernardes SF, Lima ML
Abstract
Although women report feeling more pain than men their pain is often under-valued as compared to men’s pain. We argue that such biases are not universal, being either enhanced or suppressed by context-related variables pertaining to the situation, the patient and the perceiver. Consequently, we aimed at understanding the effects of pain duration, patient’s distress and the judge’s sex on sex-related biases in pain judgements. Two-hundred and five nursing students (44.9% male) participated in a between-subjects design, 2 (pain duration)×2 (patient’s distress)×2 (patient’s sex)×2 (participant’s sex). Participants read a vignette depicting a man/woman going into an Emergency Room complaining of low-back pain, that he/she had had for 3days/years, with/without signs of distress. Afterwards, participants judged the: (1) clinical severity/urgency; (2) pain credibility; and (3) pain disability. Findings showed that sex-related biases were only evident when pain was acute or expressed without distress. In these cases, the woman’s clinical situation was perceived as less severe/urgent and her pain as less credible as compared to the man’s. Moreover, only the judgments on the woman’s pain were moderated by such contextual variables. Finally, male students were more biased than females. Implications for gender equality in pain treatments are drawn.
PMID: 21530337 [PubMed - in process]
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