The journal of pain : official journal of the American Pain Society
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Pregabalin is used for treatment of neuropathic pain conditions. The present study evaluated effects of pregabalin in 2 rat models of muscle-induced hyperalgesia: Inflammatory and noninflammatory. Muscle hyperalgesia (withdrawal threshold to compression of the muscle) and cutaneous hyperalgesia of the paw (withdrawal threshold to von Frey filaments) were measured before and after induction of hyperalgesia and after treatment with pregabalin (saline, 10 to 100 mg/kg i.p.). In the inflammatory model, 3% carrageenan injected into 1 gastrocnemius muscle decreased the mechanical withdrawal threshold of the paw bilaterally and the compression withdrawal threshold of the muscle ipsilaterally 2 weeks later. Pregabalin (10 to 100 mg/kg) increased the compression withdrawal threshold of the inflamed muscle when compared with vehicle controls. Pregabalin also increased the mechanical withdrawal threshold of the paw bilaterally, but only with 100 mg/kg. In the noninflammatory model, 2 unilateral injections of acidic saline into the gastrocnemius muscle produced bilateral cutaneous and muscle hyperalgesia 24 hours after the second injection. Pregabalin (10 to 100 mg/kg i.p.) significantly increased the compression withdrawal thresholds of the muscle and the mechanical withdrawal threshold of the paw bilaterally when compared with vehicle. However, pregabalin also has significant motor effects at the higher doses (60 to 100 mg/kg). Therefore, pregabalin reduces both muscle and cutaneous hyperalgesia that occurs after muscle insult in 2 animal models of muscle pain at doses that do not produce ataxia. ⋯ This study shows that pregabalin reduces both cutaneous and muscle hyperalgesia in inflammatory and noninflammatory models of muscle pain. Thus, pregabalin may be an effective treatment for people with chronic muscle pain.
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The aim of the present study was to evaluate ethnic differences of the tactile detection threshold (TDT), the filament-prick pain detection threshold (FPT), the pressure pain detection threshold (PPT), and the pressure pain tolerance detection threshold (PTOL) in the orofacial region of symptom-free subjects. Twenty-two men and 22 women in Belgium and in Japan (age range from 20 to 31 years) participated. The TDT and the FPT were measured on the cheek skin (CS) overlying the masseter muscles (MM), on the maxillary gingiva (MG), and at the tip of the tongue (TT), using Semmes-Weinstein monofilaments. The PPT and PTOL were measured at the central part of the MM, using a pressure algometer. A general linear model was used in each case to capture ethnic and gender effects. Japanese women had the lowest TDT at CS, in contrast to Belgian men, who had the highest value; a significant ethnic and gender effect was found (P=.026 and P<.001, respectively). Similar results were found for FPT at CS with significant ethnic and gender effects (P<.001 for both). There was no significant ethnic effect regarding intra-oral TDT and FPT or regarding PPT and PTOL. ⋯ Our findings clearly indicate that future studies of tactile and pain measurements need to standardize and control for gender and ethnicity. Further, a comprehensive evaluation of results from various stimulation modalities may better clarify the pain mechanisms and gender/ethnic characteristics, as well as comparisons between normal subjects and patients.
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We examined the relation between repeated noxious pressure over the trapezius muscle and changes in pressure pain thresholds (PPTs) in a before-after trial design. A conditioning series of 30 mechano-nociceptive stimuli was applied manually with a handheld algometer probe, and PPTs were measured over 1 trapezius muscle (skin anaesthetized) in 27 healthy women before and after the intervention. With a mean stimulation rate of 0.40 Hz and a mean nociceptive stimulation intensity of 1.78 x Threshold, subjects were found to systematically react with a change in PPT, either a decrease or an increase. Normalized data, transformed into mean unidirectional PPT differences, showed statistically highly significant changes after intervention. The relative risk of reacting with lowered PPTs on noxious stimulation was 3.7 times higher for subjects who had not given birth to children than for subjects who had given birth to 1 or several children (P<.046). When 11 subjects were tested at a second session, a clear correlation of PPT reactions (r=0.527; P<.001) was found. In summary, repetitive mechano-nociceptive stimulation of the trapezius muscle in healthy females evokes moderate and temporary changes in PPT that last for at least 35 minutes after cessation of stimulation. ⋯ A possible development of the response with transiently decreased PPTs into a model for human muscle pain is an intriguing possibility, since other models usually involve the introduction of chemical or thermal agents in the muscle, but this must await further research.
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Randomized Controlled Trial Comparative Study
Assessor status influences pain recall.
Anecdotal clinical reports suggest that patients report differing levels of pain, depending on the status within the medical hierarchy of the individual gathering the pain rating. This observation has clinical relevance, given the practice of delegating the assessment of pain to lower status clinic staff members. In this study, both pain and mood were assessed in 70 patients diagnosed with low back pain at pretreatment, immediately after epidural lumbar injection, and again 2 weeks later by phone. At the 2-week follow-up, patients were also asked to recall the postprocedural rating that they had given immediately after the injection. This rating was obtained by either the treating physician or by a research assistant who was present at the time of injection, on a randomly determined basis. Current ratings of pain and mood did not differ for either group before the epidural injection, after the epidural injection, or at the 2-week follow-up. Two-week recall of postprocedural pain did, however, differ depending on assessor status. Those called by the physician provided recalled pain ratings that closely matched the ratings provided immediately after the procedure. Those called by the research assistant provided ratings that were 86% higher (that is, worse) than their original ratings. This status-driven bias in recalled postprocedural pain reporting is discussed in the context of social demands inherent in the physician-patient relationship, with implications for assessing treatment effectiveness in clinical practice and research. ⋯ Accurate assessment of patients' pain is critical to effective pain management and treatment planning. This study found evidence of a status-based bias in which physicians elicited lower ratings of previously experienced pain associated with treatment procedures than did staff members of lower status.
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Prior research has found that pain catastrophizing measured before pain testing is not correlated with the nociceptive flexion reflex (NFR) threshold (a measure of spinal nociception), suggesting that catastrophizing does not alter pain through descending modulatory mechanisms. However, recent evidence suggests that in vivo catastrophizing (measured during or after pain testing) is a better predictor of pain outcomes. In the present study, NFR threshold and pain sensation ratings were assessed in 78 healthy participants by delivering electric stimulations to the sural nerve. After pain testing, participants were asked to rate their affective reaction (displeasure, arousal) to electric stimuli and to report on their pain catastrophizing. Hierarchical regression analyses controlling for participant sex, pre-experiment affect, depressive symptoms, and self-efficacy were used to predict pain-related outcomes (NFR threshold, pain sensation, displeasure ratings, arousal ratings) from in vivo catastrophizing scores. Results indicated that in vivo catastrophizing was related to pain sensation but not to NFR thresholds or arousal reactions. The relation between in vivo catastrophizing and displeasure ratings was not significant after other variables were controlled. These data support prior research suggesting that catastrophizing does not alter pain by engaging descending modulatory mechanisms. ⋯ Pain catastrophizing is an important psychological predictor of pain and pain-related functioning. The present study confirms prior reports suggesting that catastrophizing does not work by engaging mechanisms that alter pain transmission in the spinal cord before the signal travels to the brain.