Endogenous Pain Modulation Induced by Extrinsic and Intrinsic Psychological Threat in Healthy Individuals

Many factors interact to influence threat perception and the subsequent experience of pain. This study investigated the effect of observing pain (extrinsic threat) and intrinsic threat of pain to oneself on pressure pain threshold (PPT). Forty socially connected pairs of healthy volunteers were threat-primed and randomly allocated to experimental or control roles. An experimental pain modulation paradigm was applied, with non-nociceptive threat cues used as conditioning stimuli. In substudy 1, the extrinsic threat to the experimental participant was observation of the control partner in pain. The control participant underwent hand immersion in noxious and non-noxious water baths in randomized order. Change in the observing participant's PPT from baseline to mid- and postimmersion was calculated. A significant interaction was found for PPT between conditions and test time (F_2,78?=?24.9, P?<?.005). PPT increased by 23.6%?±?19.3% between baseline and during hand immersion (F_1,39?=?43.7, P?<?.005). Substudy 2 investigated threat of imminent pain to self. After a 15-minute break, the experimental participant's PPT was retested (“baseline 2”). Threat was primed by suggestion of whole arm immersion in an icier, larger water bath. PPT was tested immediately before anticipated arm immersion, after which the experiment ended. A significant increase in PPT between “baseline 2” and “pre-immersion” was seen (t?=??7.6, P?=?.005), a pain modulatory effect of 25.8?±?20.7%. Extrinsic and intrinsic threat of pain, in the absence of any afferent input therefore influences pain modulation. This may need to be considered in studies that use noxious afferent input with populations who show dysfunctional pain modulation.

Acupuncture for Chronic Pain: Update of an Individual Patient Data Meta-Analysis

Despite wide use in clinical practice, acupuncture remains a controversial treatment for chronic pain. Our objective was to update an individual patient data meta-analysis to determine the effect size of acupuncture for 4 chronic pain conditions. We searched MEDLINE and the Cochrane Central Registry of Controlled Trials randomized trials published up until December 31, 2015. We included randomized trials of acupuncture needling versus either sham acupuncture or no acupuncture control for nonspecific musculoskeletal pain, osteoarthritis, chronic headache, or shoulder pain. Trials were only included if allocation concealment was unambiguously determined to be adequate. Raw data were obtained from study authors and entered into an individual patient data meta-analysis. The main outcome measures were pain and function. An additional 13 trials were identified, with data received for a total of 20,827 patients from 39 trials. Acupuncture was superior to sham as well as no acupuncture control for each pain condition (all P?<?.001) with differences between groups close to .5 SDs compared with no acupuncture control and close to .2 SDs compared with sham. We also found clear evidence that the effects of acupuncture persist over time with only a small decrease, approximately 15%, in treatment effect at 1 year. In secondary analyses, we found no obvious association between trial outcome and characteristics of acupuncture treatment, but effect sizes of acupuncture were associated with the type of control group, with smaller effects sizes for sham controlled trials that used a penetrating needle for sham, and for trials that had high intensity of intervention in the control arm. We conclude that acupuncture is effective for the treatment of chronic pain, with treatment effects persisting over time. Although factors in addition to the specific effects of needling at correct acupuncture point locations are important contributors to the treatment effect, decreases in pain after acupuncture cannot be explained solely in terms of placebo effects. Variations in the effect size of acupuncture in different trials are driven predominantly by differences in treatments received by the control group rather than by differences in the characteristics of acupuncture treatment.

The Effect of Pain on Major Cognitive Impairment in Older Adults

Older adults frequently report pain; cross-sectional studies have shown that pain is associated with worse cognitive function. However, longitudinal studies are lacking. We prospectively studied 441 participants without dementia, including 285 with pain, aged 65 years and older, enrolled in the Central Control of Mobility in Aging study, a prospective cohort study. We analyzed the longitudinal association between pain (measured with the Medical Outcomes Study pain severity scale) and major cognitive impairment (measured with the Repeatable Battery for the Assessment of Neuropsychological Status and the Trail Making Test Delta) using Cox regression analysis adjusted for age, gender, ethnicity, and education. Over a mean follow-up of 2.75 years (standard deviation?=?1.94), there was no difference in the risk of developing cognitive impairment between participants with pain and participants without pain. However, among those with pain, risk for developing major memory impairment was higher among those with high levels of pain than those with low levels of pain (adjusted hazard ratio?=?3.47, 95% confidence interval?=?1.42–8.46). The association with pain and incident impairments in attention or executive function was not significant. We did not find that pain is associated with incident cognitive impairment in general, but among older adults with pain, a high level of pain is associated with increased risk of developing incident memory impairment.

Sex and Race Differences in Pain Sensitization among Patients with Chronic Low Back Pain

Growing evidence suggests that chronic low back pain (CLBP) is associated with pain sensitization, and that there are sex and race disparities in CLBP. Given the sex and race differences in pain sensitization, this has been hypothesized as a mechanism contributing to the sex and race disparities in CLBP. This study examined sex and race differences in pain sensitization among patients with CLBP, as well as the role of catastrophizing as a potential mediator of those differences. The study found that compared with men, women required less pressure to produce deep muscle pain and rated mechanical punctate pain as more painful. Compared with non-Hispanic white patients, black patients demonstrated greater pain sensitivity for measures of deep muscle hyperalgesia and mechanical punctate pain. Furthermore, catastrophizing partially mediated the race differences in deep muscle pain such that black participants endorsed greater pain catastrophizing, which partially accounted for their increased sensitivity to, and temporal summation of, deep muscle pain. Taken together, these results support the need to further examine the role of catastrophizing and pain sensitization in the context of sex and race disparities in the experience of CLBP.

Physical and Psychosocial Factors in the Prevention of Chronic Pain in Older Age

Chronic pain is recognized as a major challenge as people age. Yet, despite growing research on chronic pain management, there is little research into chronic pain prevention. Thus there is a clear need to identify multimodal activities that could be encouraged among older adults as part of a healthy lifestyle to decrease the incidence risk of chronic pain. Using data from the English Longitudinal Study of Ageing we tracked 2,631 adults aged ≥50 years who were free from chronic pain at baseline across a decade and explore whether physical or psychosocial factors reduced the risk of developing chronic pain. In relation to physical factors, engaging in vigorous weekly activity was protective against the development of chronic pain (odds ratio 0.74, standard error 0.07, 95% confidence interval 0.62–0.89) when controlling for all identified socioeconomic, health, and social confounders. However, no effects were found for moderate weekly activity. In relation to psychosocial factors, cultural engagement was also protective against the development of chronic pain (odds ratio 0.75, standard error 0.07, 95% confidence interval 0.63–0.91), but community group participation was not. These findings extend previous work showing that physical activity and psychosocial factors such as positive affect are key factors in the long-term success of chronic pain self-management. Future interventional studies for chronic pain are encouraged.