Pain
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The hyperalgesic effects of long-term opioid use in community-dwelling adults with chronic pain have not been widely reported. Therefore, the primary aim of this study was to determine the associations between opioid use and heat pain (HP) perception in a sample of community-dwelling adults with chronic pain. The study cohort involved 187 adults (85 opioid and 102 nonopioid) with chronic pain consecutively admitted to an outpatient interdisciplinary pain treatment program. ⋯ In univariable (P = 0.019) and multiple variable (P = 0.003) linear regression analyses (adjusted for age, sex, body mass index, work status, pain diagnosis, pain severity, depression, and pain catastrophizing), opioid use was associated with lower (more hyperalgesic) nonstandardized values of HP 5-0.5. Similarly, in univariable (P = 0.004) and multiple variable (P = 0.011) linear regression analyses (adjusted for work status, pain diagnosis, pain severity, depression, and pain catastrophizing), opioid use was associated with lower standardized values of HP 5-0.5. In this sample of community-dwelling adults, these observations suggest that long-term opioid use was associated with hyperalgesia independent of other clinical factors known to influence HP perception.
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Randomized Controlled Trial
Delayed Onset Muscle Soreness: pilot study to assess analgesic study design features.
Based on a thorough review of the available literature in the delayed-onset muscle soreness (DOMS) model, we identified multiple study design characteristics that are considered to be normative in acute pain research but have not been followed in a majority of published DOMS experiments. We designed an analgesic investigation using the DOMS model that both complied with current scientifically accepted standards for the conduct of analgesic studies and demonstrated reasonable assay sensitivity. This randomized, double-blind, placebo-controlled within-subject study compared the efficacy of topical diclofenac sodium 1% with a matching placebo in reducing pain associated with DOMS. ⋯ This investigation used experimental techniques that have been vetted in the field of exercise physiology and superimposed techniques that are considered to be best practice in the field of analgesic research. Over time and with the help of colleagues in both fields of study, similar investigations will validate design features that impact the assay sensitivity of analgesic end points in DOMS models. In addition, the study confirmed the analgesic efficacy of topical DSG 1% over placebo in subjects experiencing DOMS.
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Electrical stimulation of low-threshold Aβ-fibers (Aβ-ES) is used clinically to treat neuropathic pain conditions that are refractory to pharmacotherapy. However, it is unclear how Aβ-ES modulates synaptic responses to high-threshold afferent inputs (C-, Aδ-fibers) in superficial dorsal horn. Substantia gelatinosa (SG) (lamina II) neurons are important for relaying and modulating converging spinal nociceptive inputs. ⋯ These findings show that activities in Aβ-fibers lead to frequency-dependent depression of synaptic transmission in SG neurons in response to peripheral noxious inputs. However, 50-Hz Aβ-ES failed to induce cell-type-selective inhibition in SG neurons. The physiologic implication of this novel form of synaptic depression for pain modulation by Aβ-ES warrants further investigation.
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Review Meta Analysis
How does pain lead to disability? A systematic review and meta-analysis of mediation studies in people with back and neck pain.
Disability is an important outcome from a clinical and public health perspective. However, it is unclear how disability develops in people with low back pain or neck pain. More specifically, the mechanisms by which pain leads to disability are not well understood. ⋯ We found evidence to show that self-efficacy (β = 0.23, 95% confidence interval [CI] = 0.10 to 0.34), psychological distress (β = 0.10, 95% CI = 0.01 to 0.18), and fear (β = 0.08, 95% CI = 0.01 to 0.14) mediated the relationship between pain and disability, but catastrophizing did not (β = 0.07, 95% CI = -0.06 to 0.19). The methodological quality of these studies was low, and we highlight potential areas for development. Nonetheless, the results suggest that there are significant mediating effects of self-efficacy, psychological distress, and fear, which underpins the direct targeting of these constructs in treatment.