Reduced endogenous pain inhibition in adolescent girls with chronic pain

Abstract

Background and aims Chronic pain is affecting a growing number of individuals including adolescents. Different endogenous pain inhibitory systems could confer protection against development of chronic pain. Decreased pain perception can be observed following intense pain (i.e. conditioned pain modulation - CPM) or after physical exercise (i.e. exercise-induced analgesia - EIA). Reduced effectiveness of pain inhibitory mechanisms have been reported in several chronic pain conditions. However, the extent of these dysfunctions has not been thoroughly investigated in adolescents suffering from chronic pain. Our hypothesis was that adolescents suffering from chronic pain have less effective CPM and EIA than pain-free teenagers. Methods Twenty-five healthy adolescent girls and 16 teenage girls with chronic pain participated in this study. Only girls were included in this investigation, since chronic pain is more prevalent in females. The effectiveness of CPM was assessed by comparing heat pain stimulations (individually adapted to induce mild pain intensity) performed with a thermode before and after a cold pressor test (CPT; 2 min, 10 °C). EIA was evaluated by comparing pain intensity produced by an ice cube placed on the forearm before and after a graded exercise test on a cycle ergometer. Results Pain intensity produced by heat pain stimulations decreased following CPT in healthy (p<0.05), but not in chronic pain adolescent girls (p=0.4). Pain intensity induced by the ice cube was reduced after exercise in healthy (p<0.05), but not in chronic pain adolescents (p=0.9). The effectiveness of CPM and EIA was inferior in teenage girls suffering from chronic pain compared to healthy participants (p<0.05). Conclusions Endogenous pain inhibitory mechanisms triggered by intense pain or by physical exercise are effective in healthy adolescent girls. Teenage girls living with chronic pain do not show diminished pain perception after a CPT or a graded exercise test. These results suggest that pain inhibitory mechanisms such as CPM and EIA are ineffective in adolescent girls suffering from chronic pain. Implications In a wider context, the findings of the present research could help understand better the mechanisms involved in the development of chronic pain. Improved comprehension of this subject might help prevent chronic pain conditions and thus, reduce the negative impacts of this burden.

Keywords: adolescent; chronic pain; conditioned pain modulation; exercise-induced analgesia; physical exercise.