Trajectories of pain predict disabilities affecting daily living in arthritis.

PURPOSE: To examine the interplay between pain and disability in arthritis when adjusting for patient heterogeneity in pain progression. There is consistent evidence to suggest that people experience osteoarthritis heterogeneously, with subgroups of people having different trajectories of pain. However, at present it is unclear how these pain trajectories are related to functional disability. We ask the question: Do levels of disability track changes in pain across different pain trajectories?

METHODS: Secondary analysis of a subset (n = 889) from a cohort of older English adults, representative of the general population (the English Longitudinal Study of Ageing). The relationship between pain and functional disability was compared in three domains of disability: mobility, activities of daily living (ADL) and instrumental ADL. These represent increasingly complex forms of self-care required for independent living. Data analysis compared the heterogeneous analysis of pain (different trajectories) and disability compared to treating pain as a simpler homogenous construct.

RESULTS: On a population level, pain was significantly positively correlated with increased disability in all three domains, and the relationship remained stable over time. However, when heterogeneity was examined respondents whose pain improved did not show a corresponding improvement in disability in two domains (ADL and mobility).

CONCLUSIONS: These findings highlight how, for some people, alleviating pain, the main symptom of arthritis, might not prevent the persistence or progression of disability. Even when pain improves, further interventions that improve disability are likely to be required. Statement of contribution What is already known on this subject? Pain and functional limitation in daily living are common symptoms of arthritis. Arthritis pain is heterogeneous - there are trajectories of people whose pain gets better or worse. However, to date no study has looked at the relationship between trajectories of arthritis pain and functional disability outside of the minority of people with rheumatoid arthritis. What does this study add? Treating pain as heterogeneous explained disability better than treating pain as a single entity. Respondents in a trajectory of worsening pain reported functional disability in two domains (mobility and activities of daily living) also got worse over time. People in a trajectory of decreasing pain over time did not experience a reduction in disability, despite pain being the most common reason for why people limit their daily functioning. This suggests further intervention is required for people with arthritis, even when the most visible symptoms have been alleviated.