The journal of pain : official journal of the American Pain Society
-
Although stress induces analgesia, there is evidence that stressful events may exacerbate pain syndromes. Here, we studied the effects of 1 to 3 prestressful events (days 0, 2, and 7), such as non-nociceptive environmental stress, on inflammatory hyperalgesia induced by a carrageenan injection (day 14) in 1 rat hind paw. Changes in nociceptive threshold were evaluated by the paw pressure vocalization test. The higher the number of stress sessions presented to the rats, the greater was the inflammatory hyperalgesia. Blockade of opioid receptors by naltrexone before each stress inhibited stress-induced analgesia and suppressed the exaggerated inflammatory hyperalgesia. Stressed versus nonstressed animals could be discriminated by their response to a fentanyl ultra-low dose (fULD), that produced hyperalgesia or analgesia, respectively. This pharmacological test permitted the prediction of the pain vulnerability level of prestressed rats because fULD analgesic or hyperalgesic indices were positively correlated with inflammatory hyperalgesic indices (r(2) = .84). In prestressed rats, fULD-induced hyperalgesia and the exaggerated inflammatory hyperalgesia were prevented NMDA receptor antagonists. This study provides some preclinical evidence that pain intensity is not only the result of nociceptive input level but is also dependent on the individual history, especially prior life stress events associated with endogenous opioid release. ⋯ Based on these preclinical data, it would be of clinical interest to evaluate whether prior stressful events may also affect further pain sensation in humans. Moreover, this preclinical model could be a good tool for evaluating new therapeutic strategies for relieving pain hypersensitivity.
-
Randomized Controlled Trial Multicenter Study
Early improvement in pain predicts pain response at endpoint in patients with fibromyalgia.
An unanswered, but clinically important question is whether there are early indicators that a patient might respond to duloxetine treatment for fibromyalgia pain. To address this question, pooled data from 4 double-blind, placebo-controlled trials in duloxetine-treated patients (N = 797) with primary fibromyalgia as defined by the American College for Rheumatology were analyzed. Classification and Regression Tree (CART) analysis was used to determine what level of early pain improvement as measured by the 24-hour average pain severity question on the Brief Pain Inventory (BPI) best predicted later response. The predictor variables tested were 10, 15, 20, 25, and 30% decrease in BPI 24-hour average pain from baseline to Week 1 and Week 2. The results of the CART analysis showed that for patients with ≥15% improvement in pain at Week 1 and ≥30% improvement at Week 2, the probability of response at 3 months was 75%. For patients with <15% improvement at both Week 1 and Week 2, the probability of not responding at 3 months was 86%. Quantifiable early improvement in pain during the first 2 weeks of treatment with duloxetine was highly predictive of response or nonresponse after 3 months of treatment. ⋯ This article presents early indicators that can highly predict later pain response or nonresponse in fibromyalgia patients treated with duloxetine. The results may aid clinicians to predict the likelihood of response at 3 months within the first 2 weeks of treatment.
-
Review Case Reports
Understanding and treating opioid addiction in a patient with cancer pain.
-
Activity patterns are believed to play an important role in the development and perpetuation of chronic pain. So far, 3 important activity patterns have been studied: avoidance behavior, persistence behavior, and pacing behavior. Yet, empirical evidence is limited and inconclusive about the relationships between these activity patterns and important outcomes. Therefore, the present study was aimed at identifying activity patterns by means of factor analyses and determining their relationship with disability and depressive symptomatology in participants with chronic pain (N = 132). Items across different measurement instruments pertaining to 1 particular activity pattern were aggregated, and submitted to factor analysis. Results from 3 separate factor analyses revealed 6 distinct activity patterns: pain avoidance, activity avoidance, task-contingent persistence, excessive persistence, pain-contingent persistence, and pacing. In line with our hypotheses, pain and activity avoidance, and excessive persistence, were related to higher levels of disability and depressive symptomatology. In contrast to hypotheses, pacing was associated with worse outcomes as well. Interestingly, task-contingent persistence was related to lower levels of disability and depressive symptomatology. When controlling for pain and the other activity patterns, excessive persistence and activity avoidance were the most detrimental in terms of relations with depressed mood or disability. Task-contingent persistence appeared to be the least detrimental. ⋯ Our findings suggest the existence of several activity patterns, which are differentially related to disability and depressive symptomatology, in participants with chronic pain. The present results are discussed in the light of previous findings, and may provide a new impetus for future studies on activity patterns in chronic pain research.
-
Myofascial pain syndrome (MPS) is an important clinical condition characterized by chronic muscle pain and a myofascial trigger point (MTrP) located in a taut band (TB). However, its pathogenic mechanism is still unclear. We developed an animal model relevant to conditions of MPS, and analyzed the mechanism of the muscle pain in this model. We applied eccentric contraction (EC) to a rat's gastrocnemius muscle (GM) for 2 weeks, and examined the mechanical withdrawal thresholds, histological changes, and expressions and contents of nerve growth factor (NGF). The mechanical withdrawal threshold decreased significantly at the next day of first EC and continued up to 9 days after EC. TBs were palpable at 3 to 8 days after initiation of EC. In EC animals, necrotic and regenerating muscle cells were found significantly more than in control animals. In EC animals, NGF expressions in regenerating muscle cells and NGF contents of GM were significantly higher than control animals. Administration of NGF receptor (TrkA) inhibitor K252a showed significant suppression of mechanical hyperalgesia in EC animals. Repeated EC induced persistent mechanical muscle hyperalgesia associated with TB. NGF expressed in regenerating muscle cells may have an important role in persistent mechanical muscle hyperalgesia which might be relevant to pathogenesis of MPS. ⋯ The present study shows that NGF expressed in regenerating muscle cells is involved in persistent muscular mechanical hyperalgesia. NGF-TrkA signaling in primary muscle afferent neurons may be one of the most important and promising targets for MPS.