Patterns of pain over time among children with Juvenile Idiopathic Arthritis

Objectives
Pain is a very common symptom of juvenile idiopathic arthritis (JIA). Disease-activity alone cannot explain symptoms of pain in all children, suggesting other factors may be relevant. The objectives of this study were to describe the different patterns of pain experienced over time in children with JIA and to identify predictors of which children are likely to experience on-going pain.

Methods
This study used longitudinal-data from patients (aged 1-16 years) with new-onset JIA. Baseline and up to 5-year follow-up pain data from the Childhood Arthritis Prospective Study (CAPS) were used. A two-step approach was adopted. First, pain trajectories were modelled using a discrete mixture-model. Second, multinomial logistic regression was used to determine the association between variables and trajectories.

Results
Data from 851 individuals were included (four years, median follow-up). A three-group trajectory model was identified: consistently-low pain (n=453), improved-pain (n=254) and consistently-high pain (n=144). Children with improved-pain or consistently-high pain differed on average at baseline from consistently-low pain. Older age at onset, poor function/disability and longer disease-duration at baseline were associated with consistently-high pain compared to consistently-low pain. Early increases in pain and poor function/disability were also associated with consistently-high pain compared to consistently-low pain.

Conclusions
This study has identified routinely collected clinical factors, which may indicate those individuals with JIA at risk of poor pain-outcomes earlier in disease. Identifying those at highest risk of poor pain-outcomes at disease onset may enable targeted pain management strategies to be implemented early in disease thus reducing the risk of poor pain-outcomes.
Funding: ARUK Grant Reference number 20542