Pain
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Observational Study
National Breakthrough Pain Study: prevalence, characteristics, and associations with health outcomes.
The National Breakthrough Pain Study is a large observational study that assessed breakthrough pain (BTP) in a population of commercially insured community-dwelling patients with opioid-treated chronic pain. Eligible patients were identified from an administrative claims database, and consenting patients were asked to complete a structured telephone interview and several validated questionnaires. Questionnaires assessed pain interference with function (Brief Pain Inventory-Short Form), health status (Short Form 12 [SF-12] Health Survey), disability (Sheehan Disability Scale), work performance (World Health Organization Health and Work Performance Questionnaire), and mood (Generalized Anxiety Disorder-7 Screener [GAD-7] and Patient Health Questionnaire-2 [PHQ-2]). ⋯ Compared with patients without BTP, patients with BTP had more pain-related interference in function (Brief Pain Inventory, mean ± SD: 34.2 ± 15.6 vs 25.0 ± 15.7 [P < 0.001]), worse physical health (SF-12 physical component score: 29.9 ± 9.6 vs 35.1 ± 10.4 [P < 0.001]) and mental health (SF-12 mental component score: 47.4 ± 11.3 vs 49.3 ± 10.4 [P < 0.001]), more disability (Sheehan Disability Scale global impairment score: 15.1 ± 9.1 vs 10.6 ± 8.5; World Health Organization Health and Work Performance Questionnaire absolute absenteeism: 12.4 ± 59.9 vs 7.7 ± 44.9 hours [both P < 0.001]), and worse mood (GAD-7 score: 7.4 ± 5.9 vs 5.9 ± 5.4; PHQ-2 anhedonia score: 1.2 ± 1.1 vs 0.9 ± 1.0 [both P < 0.001]). In this population of community-dwelling patients with opioid-treated chronic pain, BTP was highly prevalent and associated with negative outcomes. This burden of illness suggests the need for specific treatment plans.
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Review Meta Analysis
Early changes in somatosensory function in spinal pain: a systematic review and meta-analysis.
Alterations in sensory processing have been demonstrated in chronic low back and neck pain. However, it has not been yet systematically summarized how early these changes occur in spinal pain. This systematic review examines the available literature measuring somatosensory function in acute (<6 weeks) and subacute (6-12 weeks) spinal pain. ⋯ Sources of bias included lack of assessor blinding, unclear sampling methods, and lack of control for confounders. We found that: (1) there is consistent evidence for thermal and widespread mechanical pain hypersensitivity in the acute stage of whiplash, (2) there is no evidence for pain hypersensitivity in the acute and subacute stage of idiopathic neck pain, although the body of evidence is small, and (3) hyperalgesia and spinal cord hyperexcitability have been detected in early stages of nonspecific low back pain, although evidence about widespread effects are conflicting. Future longitudinal research using multiple sensory modalities and standardized testing may reveal the involvement of somatosensory changes in the development and maintenance of chronic pain.
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Osteoarthritis (OA) of the knee is a progressive disease that is associated with inflammation of the joints and lower extremity pain. Total knee arthroplasty (TKA) is a surgical procedure that aims to reduce pain and restore motor function in patients suffering from OA. The immediate postoperative period can be intensely painful leading to extended recovery times including persistent pain. ⋯ Similarly, synovial fluid levels of the anti-inflammatory lipid palmitoylethanolamide correlated with functional disability in OA. Taken together, our results are the first to reveal associations between central and peripheral endocannabinoid levels and postoperative pain. This suggests that endocannabinoid metabolism may serve as a target for the development of novel analgesics both for systemic or local delivery into the joint.
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Neuropathic pain is an important public health problem for which only a few treatments are available. Preclinical studies show that melatonin (MLT), a neurohormone acting on MT1 and MT2 receptors, has analgesic properties, likely through MT2 receptors. Here, we determined the effects of the novel selective MLT MT2 receptor partial agonist N-{2-([3-bromophenyl]-4-fluorophenylamino)ethyl}acetamide (UCM924) in 2 neuropathic pain models in rats and examined its supraspinal mechanism of action. ⋯ Using double staining immunohistochemistry, we found that MT2 receptors are expressed by glutamatergic neurons in the rostral ventrolateral periaqueductal gray. Using in vivo electrophysiology combined with tail flick, we observed that microinjection of UCM924 into the ventrolateral periaqueductal gray decreased tail flick responses, depressed the firing activity of ON cells, and activated the firing of OFF cells; all effects were MT2 receptor-dependent. Altogether, these data demonstrate that selective MT2 receptor partial agonists have analgesic properties through modulation of brainstem descending antinociceptive pathways, and MT2 receptors may represent a novel target in the treatment of neuropathic pain.
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The descending noradrenergic (NAergic) projection to the spinal cord forms part of an endogenous analgesic system. After nerve injury, a localised failure in this compensatory system has been implicated as a permissive factor in the development of neuropathic sensitisation. We investigated whether restoring descending NAergic tone with intrathecal reboxetine can oppose the development of the neuropathic pain phenotype after tibial nerve transection (TNT). ⋯ In contrast, an equivalent antiallodynic dose of systemic reboxetine (30 mg/kg) was aversive in both naive and TNT rats. On cessation of chronic intrathecal reboxetine, there was a gradual development of allodynic sensitisation that was indistinguishable from control TNT animals by 7 days after the end of dosing. Our results suggest that pharmacological restoration of spinal NAergic tone with intrathecal reboxetine can suppress both allodynia and spontaneous pain in the TNT model.