The journal of pain : official journal of the American Pain Society
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Randomized Controlled Trial
The Opportunity to Avoid Pain May Paradoxically Increase Fear.
Fear-avoidance models propose that pain-related fear may spur avoidance behavior leading to chronic pain disability. Pain-related fear elicits avoidance behavior, which is typically aimed at reducing fear. We hypothesized that engaging in avoidance may (paradoxically) increase rather than decrease pain-related fear (ie, bidirectionality hypothesis). ⋯ Interestingly, in the avoidance group, pain-related fear increased after receiving instructions that avoidance would be possible, even before actually engaging in avoidance behavior. In the control group, no significant change was observed in pain-related fear throughout the experiment. The eyeblink startle measures did not corroborate this data pattern.
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Facilitated pain mechanisms have been demonstrated in musculoskeletal pain, but it is unclear whether a recent painful injury leaves the pain system sensitized. Pain characteristics were assessed in individuals who recently recovered from ankle pain (recovered pain group; n = 25) and sex-matched control subjects (n = 25) in response to tonic pressure pain and saline-induced pain applied at the shin muscle. Pain intensity and pain referral patterns were recorded bilaterally after the painful muscle stimulus. ⋯ Compared with in control subjects, saline-induced and pressure-induced pain in the shin muscle were more frequently felt as referred pain in the previously painful ankle (P < .05), and the pain area within the previously affected ankle was larger after saline-induced pain (P < .05). In the recovered pain group, conditioned pain modulation responses and the cuff pressure needed to reach a 6-cm pain score on a 10-cm visual analog scale was higher in the previously painful leg compared with in the contralateral leg (P < .05). No group differences were found in pressure pain threshold, pain detection threshold, pain tolerance, and temporal summation of pain.
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Review Comparative Study
The Rodent Tibia Fracture Model: A Critical Review and Comparison with the Complex Regional Pain Syndrome Literature.
Distal limb fracture is the most common cause of complex regional pain syndrome (CRPS), thus the rodent tibia fracture model (TFM) was developed to study CRPS pathogenesis. This comprehensive review summarizes the published TFM research and compares these experimental results with the CRPS literature. The TFM generated spontaneous and evoked pain behaviors, inflammatory symptoms (edema, warmth), and trophic changes (skin thickening, osteoporosis) resembling symptoms in early CRPS. Neuropeptides, inflammatory cytokines, and nerve growth factor (NGF) have been linked to pain behaviors, inflammation, and trophic changes in the TFM model and proliferating keratinocytes were identified as the primary source of cutaneous cytokines and NGF. Tibia fracture also activated spinal glia and upregulated spinal neuropeptide, cytokine, and NGF expression, and in the brain it changed dendritic architecture. B cell-expressed immunoglobulin M antibodies also contributed to pain behavior, indicating a role for adaptive immunity. These results modeled many findings in early CRPS, but significant differences were also noted. ⋯ Multiple neuroimmune signaling mechanisms contribute to the pain, inflammation, and trophic changes observed in the injured limb of the rodent TFM. This model replicates many of the symptoms, signs, and pathophysiology of early CRPS, but most post-fracture changes resolve within 5 months and may not contribute to perpetuating chronic CRPS.
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Randomized Controlled Trial
Hypnosis Enhances the Effects of Pain Education in Patients With Chronic Nonspecific Low Back Pain: A Randomized Controlled Trial.
The potential benefits of combining pain education (PE) with clinical hypnosis (CH) has not yet been investigated in individuals with chronic pain. A total of 100 patients with chronic nonspecific low back pain were randomized to receive either: 1) PE alone, or 2) PE with CH. Outcomes were collected by a blinded assessor at 2 weeks and 3 months after randomization. ⋯ At 3 months, participants who received PE with CH reported lower worst pain intensity (mean difference = 1.32 points, 95% CI = .29-2.34) and catastrophizing (mean difference = 5.30 points, 95% CI = 1.20-9.41). No adverse effects in either treatment condition were reported. To our knowledge, this is the first trial showing that additional use of hypnosis with PE results in improved outcomes over PE alone in patients with chronic nonspecific low back pain.
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Clinical evidence suggests that vitamin C (Vit C) may protect against the development of complex regional pain syndrome (CRPS) after fracture or surgery. Tibia fracture followed by 4 weeks of cast immobilization (fracture/cast) in rats results in nociceptive, vascular, and bone changes resembling clinical CRPS. In this study, fracture/cast rats were treated with the oxidative stress inhibitors Vit C, N-acetyl cysteine, or 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl to examine their effects on CRPS-related nociceptive and vascular changes. ⋯ Treatments with Vit C and N-acetyl cysteine reduced the oxidative stress markers malondialdehyde in the skin, muscle, and sciatic nerve, and lactate in the gastrocnemius muscle of the fracture/cast limb. Furthermore, Vit C treatment inhibited the post-fracture upregulation of substance P and calcitonin gene-related peptide in the sciatic nerve and the increased expression of the pain-related inflammatory mediators, including interleukin (IL)-6, and nerve growth factor in the skin and IL-1β, and IL-6 in the muscle of the post-fracture/cast limb. These data suggest that oxidative stress may contribute to the nociceptive features of the rat CRPS model.