HOME-BASED TRANSCRANIAL DIRECT-CURRENT STIMULATION AND EXPERIMENTAL PAIN SENSITIVITY

Osteoarthritis (OA) of the knee is one of the most common causes of pain in older adults. Clinic-based transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that has been shown to reduce pain, but no published studies have reported using home-based self-administered tDCS in older adults with knee OA. Thus, the purpose of this study was to examine the effect of home-based tDCS on experimental pain sensitivity in older adults with knee OA. Twenty community-dwelling participants aged 50–85 years with knee OA pain received ten daily sessions of 2 mA tDCS for 20 minutes at home. A multimodal quantitative sensory testing battery was completed, including heat pain tolerance, pressure pain threshold, and punctate mechanical pain. Participants (75% female) had a mean age of 61 years, and a mean body mass index in the sample was 28.33 kg/m2. All 20 participants completed all ten home-based tDCS sessions without serious adverse effects. The Wilcoxon Signed-Rank test showed that all the differences between the baseline measurements and experimental pain sensitivity measurements after 10 sessions were statistically significant. Effect sizes (Rosenthal’s R) were R = 0.35 for heat pain tolerance (P = 0.02), R = 0.40 for pressure pain threshold (P < 0.01), and R = 0.32 for punctate mechanical pain (P = 0.02). We demonstrated that home-based self-administered tDCS was feasible and reduced experimental pain sensitivity in older adults with knee OA. Future studies with well-designed randomized controlled trials are needed to validate our findings.

The Relationship Between β-Endorphin and Experimental Pain Sensitivity in Older Adults With Knee Osteoarthritis

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.