Effects of somatic afferent stimulation in chronic musculoskeletal pain. Physiological, psychological and clinical aspects

Abstract

Although somatic afferent stimulation techniques, such as transcutaneous electrical nerve stimulation (TENS) and acupuncture, are frequently used in the treatment of chronic pain, the knowledge about which factors contribute to the pain-relieving effect is scanty. The present thesis was aimed to enlighten aspects of importance for the outcome of acupuncture and TENS treatment in chronic musculoskeletal pain. Another goal was to describe somatic and psychological characteristics of patients with chronic neck and shoulder pain. In a final study skin temperature and cardiovascular reactions during and following EA were measured to assess possible functional changes due to repeated EA sessions. Patients with chronic neck and shoulder myalgia or orofacial muscular pain recruited from pain clinics constituted the subjects in the studies. Changes in tooth pain thresholds, skin temperature, haemodynamic variables and mood variables such as stress and relaxation were evaluated in relation to acupuncture and TENS. Before and after 8 EA sessions, respectively, cervical and shoulder mobility, grip strength, muscle palpation tenderness and self-reported pain, depression and anxiety were evaluated.The results demonstrated that patients without improvement following TENS (non-responders) showed higher levels of depression and anxiety than patients with a successful outcome (responders). Non-responders showed no raised pain threshold in response to TENS in a test session after completed clinical treatment. Increased stress and reduced relaxation during acupuncture correlated with an increased pain sensitivity. A significant correlation was demonstrated between observers rating of muscle tenderness and patients self-rating of their pain. EA treatment resulted in an increased functional shoulder/arm mobility which was still significant 3 months after completed treatment. The skin temperature changed during EA stimulation. At the initial test-session skin temperature was decreased following EA, while the skin temperature increased at the test session after a series of EA treatments. This reaction remained 3 months following treatment. The thesis shows that psychological factors are of importance for the analgesic effect of acupuncture and TENS. Perceived stress during somatic afferent stimulation constitutes a negative factor for the analgesic effect. Symptoms of depression and anxiety, common in patients with chronic pain, decreased following EA and were still significantly decreased 3 months later. This effect was paralleled by significant improvement also in somatic variables