The Natural Course of Chronic Pain in a General Population: Stability and Change in an Eight-Wave Longitudinal Study Over Four Years (the HUNT Pain Study).

Epidemiological studies have to a little extent addressed the potential fluctuations of chronic pain over time, and there is a lack of information about the long-term course of pain using repeated measurements. We wanted to identify different trajectories of pain during 8 waves of follow-up over 4 years among individuals in the general population reporting pain lasting at least 6 months at baseline. Secondarily, we wanted to investigate whether biopsychosocial factors at baseline were associated with the different pain trajectories. Longitudinal Latent Class Analysis was performed to classify a random sample of 1905 participants from a larger population-based study (HUNT3) into groups based on their longitudinal pain severity reporting. A five-class solution gave the best fit. The terms chosen to describe the pain trajectories were: "fluctuating" (n = 586 [31%]), "persistent mild" (n = 449 [24%]), "persistent moderate" (n = 414 [22%]), "persistent severe" (n = 251 [13%]), and "gradual improvement" (n = 205 [11%]). In a multinomial logistic regression model using "gradual improvement" as the reference category, the "persistent moderate", "persistent severe", and "fluctuating" pain groups were associated with chronic widespread pain, elevated levels of catastrophizing, and poorer mental health. The "persistent mild" group was associated with sleep difficulties only. This study finds that although most individuals have a stable pain course, individuals in the largest distinct trajectory reports pain that fluctuate between mild and moderate levels, thus fluctuating under and above the chronic pain definition using moderate pain or more as a criterion. PERSPECTIVE: When examining the long-term course of chronic pain in the general population, 5 trajectories emerge. Although most individuals have stable pain, the largest distinct trajectory fluctuated under and above the chronic pain cut-off, using moderate pain or more as a criterion. A dichotomous categorization of chronic pain may be overly simplistic.