The journal of pain : official journal of the American Pain Society
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Randomized Controlled Trial
TENS attenuates repetition-induced summation of activity-related pain following experimentally induced muscle soreness.
This study sought to determine whether repetition-induced summation of activity-related pain (RISP) could be demonstrated in healthy individuals in response to experimentally induced musculoskeletal pain. This study also assessed the effects of transcutaneous electrical nerve stimulation on RISP. The relation between the index of RISP and psychological factors such as catastrophizing and fear of pain was also explored. The sample consisted of 56 healthy (35 women, 21 men) participants who underwent 2 testing sessions, separated by 24 hours. In the first session, musculoskeletal pain was induced with a delayed-onset muscle soreness protocol. During the second session, participants were randomly assigned to the transcutaneous electrical nerve stimulation or placebo condition and were asked to rate their pain as they lifted a series of 18 weighted canisters. An index of RISP was derived as the change in pain ratings across repeated lifts. Approximately 25% of participants showed evidence of RISP. Results also revealed that transcutaneous electrical nerve stimulation attenuated the RISP effect. Psychological measures (fear of pain, catastrophizing) were not significantly correlated with the index of RISP, but the index of RISP was significantly correlated with a measure of physical tolerance. Discussion addresses the clinical implications of the findings as well as the potential mechanisms underlying RISP. ⋯ This study showed that RISP could be demonstrated in healthy individuals in response to experimentally induced musculoskeletal pain with delayed-onset muscle soreness. Transcutaneous electrical nerve stimulation led to a significant reduction in RISP.
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Randomized Controlled Trial
An explanatory study evaluating the muscle relaxant effects of intramuscular magnesium sulphate for dystonia in complex regional pain syndrome.
The treatment of dystonia related to complex regional pain syndrome (CRPS) remains unsatisfactory, raising the need of alternative targets for intervention. In dystonia, pathologic muscle changes may occur, which contributes to stiffness. Because magnesium sulphate may act as a muscle relaxant through its actions on the neuromuscular junction and muscle, we performed an explanatory study of the muscle relaxant effect and safety of intramuscular magnesium sulphate (IMMG) in CRPS patients with dystonia. In a double-blind randomized placebo-controlled crossover study, 30 patients were assigned to 3-week treatments of IMMG and placebo. Treatments were separated by a 1-week washout period. The daily dose of IMMG was 1,000 mg in week 1, 1,500 mg in week 2, and 2,000 mg in week 3. The primary outcome measure was the difference in change in Burke-Fahn-Marsden scores after 3 weeks of treatment between both interventions. Secondary outcomes involved severity of dystonia, myoclonus, tremor, and pain, and functional activity. Data of 22 patients available for the explanatory analysis revealed no significant differences between IMMG and placebo treatment in any of the outcomes. In conclusion, we found no indication of efficacy of IMMG in a daily dose of 2,000 mg as a muscle relaxant in CRPS-related dystonia. ⋯ In this double-blind placebo-controlled crossover study there was no evidence found of a muscle relaxant effect of intramuscular magnesium sulphate in dystonia related to CRPS. Consequently, there is insufficient support for new studies evaluating the efficacy of other routes of MG administration in CRPS-related dystonia.
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Randomized Controlled Trial
Timing and gender determine if acute pain impairs working memory performance.
The effects of pain on memory are complex, and little is known about the vulnerability of working memory (WM) performance when individuals complete a WM test while concurrently experiencing pain. Here, we subjected 78 healthy nonsmoking participants to either acute pain or a control condition while we administered a WM test. In this context, we also tested WM 20 minutes after pain in order to determine if timing of pain affected WM performance, and assessed objective and subjective measures of pain. We hypothesized that pain would impair WM performance during pain. Further, women's WM performance would be impaired more than men. Importantly, there was an interaction between gender and condition, with women exposed to pain experiencing impairments during but not after the cold pressor task. Our data imply that timing and gender are critically important in whether acute pain is costly to WM performance. Our findings have interesting clinical, professional, and educational implications, and understanding the influence of pain could help to improve the interpretation of WM tests in these diverse settings. ⋯ Results of this study support the growing body of work that attests to the detrimental effect of pain on WM performance. Further, this study provides new evidence that concurrently experiencing cold pressor pain impairs WM in regularly menstruating women and women taking a contraceptive.
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Despite the high prevalence of neck pain among women, menstrual effects on regional pain outcomes have not been investigated in this clinical population. This study evaluated menstrual effects on mechanical pain sensitivity (pressure pain threshold [PPT]), neck pain intensity (numeric pain rating scale [NPRS]), and neck-related disability (Neck Disability Index [NDI]) in 22 normally menstruating (NM) and 17 hormonal contraceptive users with chronic neck pain. Sex hormones, PPT, and NDI were measured during the early follicular (F1), late follicular (F2), and luteal (L) menstrual phases. Daily NPRS scores were recorded in an online symptom diary and averaged within each phase. Estradiol and progesterone increased only for NM women in F2 and L, respectively. Phase effects on PPT (η(2) = .003), NDI (η(2) = .003), and NPRS (η(2) = .016) for NM women were small and did not differ from those for the hormonal contraceptive users (P ≥ .386). Averaged across the menstrual cycle, PPT scores explained 29% of the variance in NPRS scores for NM women but were not associated with NDI scores in either group. Results indicate that the magnitude of menstrual effects on mechanical pain sensitivity and the severity of neck pain and disability do not exceed thresholds of clinically detectable change in women with chronic neck pain. ⋯ Fluctuations in evoked and clinical pain outcomes across the menstrual cycle do not appear to be of sufficient magnitude to impact clinical decision making for women with chronic neck pain.
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Our understanding of proprioceptive deficits in complex regional pain syndrome (CRPS) and its potential contribution to impaired motor function is still limited. To gain more insight into these issues, we evaluated accuracy and precision of joint position sense over a range of flexion-extension angles of the wrist of the affected and unaffected sides in 25 chronic CRPS patients and in 50 healthy controls. The results revealed proprioceptive impairment at both the patients' affected and unaffected sides, characterized predominantly by overestimation of wrist extension angles. Precision of the position estimates was more prominently reduced at the affected side. Importantly, group differences in proprioceptive performance were observed not only for tests at identical percentages of each individual's range of wrist motion but also when controls were tested at wrist angles that corresponded to those of the patient's affected side. More severe motor impairment of the affected side was associated with poorer proprioceptive performance. Based on additional sensory tests, variations in proprioceptive performance over the range of wrist angles, and comparisons between active and passive displacements, the disturbances of proprioceptive performance most likely resulted from altered processing of afferent (and not efferent) information and its subsequent interpretation in the context of a distorted "body schema." ⋯ The present results point at a significant role for impaired central processing of proprioceptive information in the motor dysfunction of CRPS and suggest that therapeutic strategies aimed at identification of proprioceptive impairments and their restoration may promote the recovery of motor function in CRPS patients.