The role of sleep problems in a chronic pain group compared to a control group, with respect to the response in pressure pain thresholds before and after a physical activity

Abstract

Master Thesis in Medicine by Carolina Elton Supervisor: Anna Grimby-Ekman Background Chronic pain is usually defined as pain lasting more than three months. Chronic pain has a prevalence of 20% in the population and one in five of the pain patients have neck or shoulder pain. Chronic pain is more common among women than men and persons with chronic pain are more likely to have sleep problems, such as insomnia, than the general population. It is also more common with symptoms of anxiety and depression among pain patients. It has been shown that physical activity can reduce pain intensity and enhance the quality of life. Aim To investigate whether symptoms of sleep disorder are effect modifiers of the association between either the levels of Pressure Pain Thresholds (PPT) or the change in PPT due to physical activity and chronic pain. Method An experimental pain study was implemented at Occupational and Environmental Medicine Clinic, Sahlgrenska University Hospital, Gothenburg, Sweden, consisting of 26 persons (21 women, 5 men) with chronic neck pain and 12 healthy controls (7 women, 5 men), all between 18-65 years old. Pressure pain thresholds (PPT) were measured in a standardized way along both trapezius muscles and tibialis anterior muscle. Measurements were made before and after a physical activity (arm cycling). The study participants filled in a sleep diary and a sleep questionnaire (Karolinska Sleep Questionnaire) before the pain threshold measurements, which led to five sleep variables; mean sleep hours during a week (Mean Sleep), sleep hours the night before the examination (Sleep Before) and sleep quality indices regarding the presence of insomnia, awakening problems and tiredness referred to as Sleep Quality (Insomnia), Sleep Quality (Awakening) and Sleep Quality (Tiredness). Results Sleep Quality (Awakening) had significant associations with levels of PPT at both right and left trapezius (p<0.05), with lower sleep quality associated with higher PPT. Sleep Quality (Tiredness) was statistically significant associated with change in PPT after physical activity, where a decrease in PPT was seen after exercise among controls with higher Sleep Quality (Tiredness). Change in PPT after physical activity had tendencies of association with Sleep before that seemed different between the groups, for both right and left trapezius. These tendencies show that more hours slept the day before the examination predict an increase in PPT at the pair of trapezius muscles after physical exercise among controls, but not among pain subjects. An increase in levels of PPT after a physical activity among both pain and control group at tibialis anterior without any difference between groups. No statistically significant associations or tendencies were found in other variables. Conclusion Higher Sleep Quality (Awakening) predicted for lower levels of PPT in the pain group, there was a difference between the groups with a reversed pattern among the controls. Low Sleep Quality (Tiredness) among controls predicted for an increase in PPT after a physical activity and this pattern was not seen in the pain group. No clear causal factors behind these unexpected associations can be seen in the data, but confounders or a small sample size and thereby low power can contribute to the associations.