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Osteoarthritis (OA) is the most common cause of pain in people aged > 45 years, and the knee is the most commonly affected joint. There is a growing interest in understanding the biological factors that influence pain among older adults, but few studies have examined the relationship between β-endorphin and experimental pain sensitivity in older adults with knee OA pain. The purpose of this study was to investigate the relationship between resting plasma levels of β-endorphin and experimental pain sensitivity. This study was a secondary analysis of data for 40 adults with knee OA pain in whom quantitative sensory testing was used to measure experimental sensitivity to heat- and mechanically induced pain. The mean age of the sample was 60 years ( SD = 9 years), and approximately half were female (53%). Regression analyses indicated that β-endorphin level was negatively related to pressure pain threshold (β = -17.18, p = .02) and positively related to punctate mechanical pain (β = 17.13, p = .04), after controlling for age, gender, and OA severity. We did not find a significant relationship between β-endorphin and heat pain tolerance. The results suggest that higher circulating levels of β-endorphin at rest are associated with increased sensitivity to mechanical pain in older adults with knee OA. These findings add to the literature regarding biological factors associated with pain sensitivity in older adults with chronic pain. Additional studies are needed to identify mediators of the relationship between β-endorphin and pain sensitivity in OA and other musculoskeletal pain conditions.

Multiple studies in healthy populations and clinical samples have shown that ethnic minorities have greater pain sensitivity than their majority counterparts. Acculturation is speculated to be one of the sociocultural factors contributing to pain sensitivity since cultural beliefs and practices can influence the way patients perceive and respond to pain. However, the relationship of acculturation to pain sensitivity in minority populations remains poorly understood. Therefore, in this cross-sectional study, we examined the relationship between acculturation and experimental pain sensitivity in 50 Asian Americans residing in North Central Florida with knee osteoarthritis pain. The Suinn-Lew Asian Self Identity Acculturation Scale was used to assess acculturation, and multimodal quantitative sensory testing was performed to measure experimental sensitivity, including heat pain tolerance, pressure pain threshold, and punctate mechanical pain. Descriptive and regression analyses were performed. Participants' mean age was 55.7 years, and about half of this sample were Korean American (56%). The participants had lived in the United States for 21 years on average. Regression analyses indicated that lower acculturation to American culture may contribute to greater experimental pain sensitivity. Asian Americans who were more acculturated to the American culture had higher heat pain tolerance (beta = 0.61, P =0.01), higher pressure pain threshold (beta = 0.59, P =0.02), and lower ratings of punctate mechanical pain (beta = -0.70, P < 0.01). These findings add to the literature regarding sociocultural factors associated with pain in Asian Americans; additional research with a larger and more diverse sample of Asian Americans is warranted for cross-validation.

Although transcranial direct current stimulation (tDCS) is encouraging regarding clinical pain intensity for individuals with knee osteoarthritis, very few studies have explored its impact on experimental pain sensitivity, which may hinder our understanding of underlying therapeutic mechanisms. The purpose of this study was to assess the efficacy of 15 home-based tDCS sessions on experimental pain sensitivity and explore its relationships with clinical pain intensity. We randomly assigned 120 participants to active tDCS (n = 60) and sham tDCS (n = 60). Quantitative sensory testing (QST) was used, including heat pain threshold and tolerance, pressure pain threshold, and conditioned pain modulation. Patients in the active tDCS group exhibited reduced experimental pain sensitivity as reflected by all QST measures at the end of treatment. Furthermore, correlations were observed between changes in clinical pain intensity and experimental pain sensitivity. These findings warrant further studies on tDCS and experimental pain sensitivity in patients with knee osteoarthritis and exploring the magnitude and sustainability of effects on a longer term. [ABSTRACT FROM AUTHOR]

Osteoarthritis (OA) is the most prevalent cause of chronic pain and disability in people aged ≥45 years, with the knee being the most affected joint. Neurotrophic factors like brain-derived neurotrophic factor (BDNF), which promotes neurogenesis and neuroplasticity, have been shown to significantly affect chronic pain. This study aimed to investigate the relationship between resting plasma BDNF levels and clinical pain and quantitative sensory testing measures in older adults with knee OA pain. For this secondary analysis, a previously reported dataset was used comprised of older adults with knee OA who underwent quantitative sensory testing. A comprehensive generalized linear model (GLM) was built to understand the relationships between BDNF and important covariates, followed by the elastic net (EN) method for variable selection. GLM was then performed to regress BDNF levels against only the variables selected by EN. The mean age of the sample was 60.4 years (SD = 9.1). Approximately half of the participants were female (53%). Plasma BDNF levels were positively associated with heat pain threshold and the numeric rating scale of pain. Future mechanistic studies are needed to replicate and extend these findings to advance our knowledge of the underlying mechanisms of BDNF in knee OA and other chronic pain conditions. [ABSTRACT FROM AUTHOR]

Objective The present study examined the effects of home-based remotely supervised transcranial direct current stimulation on quantitative sensory testing measurements in older adults with knee osteoarthritis. Participants were hypothesized to experience improved pain measurements over time. Design Open-label, single-arm trial. Setting Southeast Texas between March and November 2018 at a nursing school and participant homes. Subjects Older adults (aged 50–85 years) with self-reported unilateral or bilateral knee osteoarthritis pain who met eligibility criteria set by the American College of Rheumatology. Methods The intervention was applied with a constant current intensity for 20 minutes every weekday for two weeks (10 total sessions). Quantitative measures of pain were collected three times over 10 days (days 1, 5, and 10) and included heat threshold and tolerance, pressure pain threshold, punctate mechanical pain, pain, and conditioned pain modulation. Analyses used nonparametric tests to evaluate differences between day 1 and day 10. Generalized linear mixed models were then used to evaluate change across all three time points for each measure. Bayesian inference was used to provide the posterior probability of longitudinal effects. Results Nonparametric tests found improvements in seven measures, and longitudinal models supported improvements in 10 measures, with some nonlinear effects. Conclusions The home-based, remotely supervised intervention improved quantitative measurements of pain in older adults with knee osteoarthritis. This study contributes to the growing body of literature supporting home-based noninvasive stimulation interventions. [ABSTRACT FROM AUTHOR]