Spatiotemporal aspects of pain in the general population; factors associated with the presence, development and distribution: Results from the HUNT2 and HUNT3 studies

Abstract

Background Chronic musculoskeletal pain among adults is a common burden to the individual, the health care system, and society, and has been estimated to affect approximately onefifth of the European population. Such pain is characterized by various periodic or continuous pain symptoms, and is associated with complex medical conditions and prominent negative consequences, and may result from many factors. The term chronic pain has several different meanings in pain medicine and is often used without a specific criterion. Chronic pain is frequently defined within temporal, spatial, qualitative, and quantitative aspects but without describing pathologic processes or identifying pain mechanisms. Spatial and temporal aspects, rather than quantity and quality aspects, of pain in the general population are the focus of this thesis. Aims To estimate the level of persistence of self-reported chronic widespread pain (CWP) at a given time (1995–1997), how many have continued having CWP at 11-year follow-up (2006–2008), and what predicts CWP persistence (Paper I). To identify how many without CWP at a given time (1995–1997) develops CWP after 11-years (2006–2008) and what predicts the development of CWP over 11 years (Paper II). To study the 11-year course of pain sites and pain locations in persons with chronic pain, and study if mood, lifestyle, and other health variables influence possible long-term changes (Paper III). With these objectives we wanted to obtain knowledge of the natural history of chronic pain over time in the general population, to obtain an overview of important prognostic psychosocial and lifestyle factors, and to study the extent to which chronic pain is stable. Method The papers included in this thesis are based on data from the Health Study of Nord- Trøndelag (HUNT), which is a large population-based survey consisting of three health surveys carried out at 11-year intervals. All papers used longitudinal prospective designs based on baseline data from the HUNT2 (1995–1997) survey and outcome data from the HUNT3 (2006–2008) survey. The population in the first two studies was restricted to those who completed both the first and second questionnaires in both HUNT2 and HUNT3. To explore our research questions we used logistic regression analyses, with baseline information on age, sex, separate anxiety and depression measures from the Hospital Anxiety and Depression Scale (HADS), alcohol use, smoking status, sleeping problems and body mass index (BMI). Variables also included education, marital status, exercise and chronic disease observed in the HUNT2 period. In the third study we added pulse as a variable of interest and used multi-level linear regression analyses, with also estimating withinsubject association. Except for BMI and pulse, all information was self-reported without objective confirmation. Chronic pain was defined as having pain and/or stiffness in muscles and limbs lasting for at least three months during the last year. CWP was defined as having chronic pain in all of the following three body areas: trunk, lower limbs and upper limbs. Results First, within an 11-year period, CWP persisted in 53% of the study participants. CWP persistence was strongly associated with those who reported sleeping problems, obesity, and having a chronic disease, while depression, anxiety, and the frequency of alcohol use were not substantial outcome predictors. Those of 60 years or older had a lower odds of CWP persistence. Second, from a baseline population free of CWP, 12% developed chronic widespread pain 11 years later. Symptoms of anxiety and/or depression, sleeping problems, and underweight/overweight/obesity appeared to be important precursors for CWP development, whereas moderate alcohol use was revealed to have a small preventive influence. Third, from the final study in the thesis, an analysis of an 11-year course of pain sites and pain locations demonstrated that differences in the mean number of pain sites were strongly associated with all variables of interest, of which alcohol use and male sex appeared as protective within the total population analyses. Changes in the number of pain sites within individuals were moderately influenced by age from 30 to 69 years, and having both anxiety and depression symptoms, sleeping problems, and chronic disease. While smoking behaviour, alcohol use, and overweight/obesity influenced the mean differences in the number of pain sites between individuals in the total population, such lifestyle factors were not of importance within individuals. The same patterns appeared when examining CWP in the total population and within individuals. Conclusions Chronic musculoskeletal pain including CWP is common in the general population and is particularly prevalent among females. Only sleeping problems, obesity and chronic disease predicted persistent CWP, and additionally, anxiety and/or depression, smoking behaviour and being underweight/overweight substantially increased the odds of developing it. Across the 11-year time period, differences in the mean number of pain sites within the total population was influenced by the same psychosocial, lifestyle and demographic factors of interests. Yet, in contrast to other findings we discovered that the number of pain sites remained unchanged or slightly decreased among the population across the time period. However, within individuals, the number of pain sites also remained constant and was influenced by aging, symptoms of both anxiety and depression, and having sleeping problems and a chronic disease