Pain
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Comparative Study
Intramuscular injection of tumor necrosis factor-alpha induces muscle hyperalgesia in rats.
The role of proinflammatory cytokines in neuropathic and inflammatory pain is well established. Recent studies suggest that cytokines such as tumor necrosis factor-alpha (TNF) may also be involved in the development of muscle pain. To investigate the pathophysiology of intramuscular TNF, exogenous TNF (0.1-10 microg), formalin (9%) or vehicle was injected into the gastrocnemius or biceps brachii muscles of rats. ⋯ TNF and formalin evoked intramuscular upregulation of CGRP and NGF, whereas PGE2 was increased exclusively after TNF injection. These findings allow us to speculate that endogenous TNF may play a role in the development of muscle hyperalgesia. Targeting proinflammatory cytokines might be beneficial for the treatment of musculoskeletal pain syndromes.
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Recent clinical studies showed that acute migraine attacks are accompanied by increased periorbital and bodily skin sensitivity to touch, heat and cold. Parallel pre-clinical studies showed that the underlying mechanism is sensitization of primary nociceptors and central trigeminovascular neurons. The present study investigates the sensory state of neuronal pathways that mediate skin pain sensation in migraine patients in between attacks. ⋯ The absence of clinically or overt laboratory expressed allodynia suggests that pain pathways are not sensitized in the pain-free migraine patients. Nevertheless, the increased temporal summation, and the slight decrease in mechanical pain thresholds, suggest that central nociceptive neurons do express activation-dependent plasticity. These findings may point to an important pathophysiological change in membrane properties of nociceptive neurons of migraine patients; a change that may hold a key to more effective prophylactic treatment.
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A patient's readiness to adopt a self-management approach to pain has been suggested as a construct that may explain differences among patients in coping, adjustment, and response to multidisciplinary pain treatment. The pain stages of change questionnaire (PSOCQ; Pain, 72 (1997) 227) was designed to assess four components of this construct. ⋯ The findings supported the first hypothesis and provided mixed support for the second. The implications of the findings for understanding the readiness to self-manage pain construct and the validity of the PSOCQ for assessing this construct are discussed.
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Comparative Study
Unilateral carrageenan injection into muscle or joint induces chronic bilateral hyperalgesia in rats.
Chronic musculoskeletal pain is a major clinical problem and there is a general lack of animal models to study this condition. Carrageenan is commonly used to produce short-lasting acute inflammation and hyperalgesia in animal models. However, the potential of carrageenan to produce chronic, long-lasting hyperalgesia has not been evaluated. ⋯ At 1 week, the inflammation converted to primarily a macrophage response with scattered mast cells. The data suggest that animals injected with 1 or 3% carrageenan in the knee joint or gastrocnemius muscle could be used as models of acute inflammation through 24 h and chronic inflammation after 1 week. Furthermore, 3% carrageenan injected into deep tissues produces hyperalgesia that spreads to the contralateral side, at the same time period as the inflammation transforms from acute to chronic.
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Attachment theory and research suggest that patterns of interpersonal relationships may be important determinants of illness behavior, care seeking, and treatment response in individuals with chronic health problems, including chronic pain. Attachment styles have been shown to be associated with psychological adjustment in the context of chronic illness, but little research has been conducted so far examining these relationships in patients with chronic pain. ⋯ Preoccupied attachment style was associated with greater than weekly pain-related visits at 12 months follow-up, even after controlling for depression, catastrophizing and pre-treatment pain-related health care utilization. The findings suggest that attachment style may be a useful construct for examining factors affecting adjustment and treatment response of patients with chronic pain.