The Longitudinal Relationship Between Pain and Depression in People with Inflammatory Arthritis: a Narrative Review.

As many patients with inflammatory arthritis (IA) have chronic pain, understanding how to best assess and manage pain in IA is a priority. Co-morbid depression is prevalent in adults with IA, affecting 15 to 39% of people. Whilst pain and depression are thought to be associated in IA, this concept is largely based on cross-sectional data. To better understand potential causality, longitudinal studies are required. This narrative review examines the relationship between pain and depression in patients with IA participating in observational longitudinal studies (spanning association strengths, direction of effect, and causal factors) and summarises the literature on causal pathways in general populations alongside guideline recommendations/systematic reviews on assessing pain/depression in IA. 14 longitudinal studies in IA largely indicate an association between pain and depression, albeit with a small-to-modest effect size, and a focus on pain intensity. This relationship appears to be bidirectional. Evidence on causal pathways is sparse in IA and limited in non-IA populations (with structural/function brain changes, altered sensory/pain thresholds, and sleep disturbance implicated) highlighting a need for further research. Whilst many patient-reported outcome measures exist to assess pain and depression in IA, evidence for their psychometric properties is often limited, and IA guidelines offer incomplete advice on pain/depression assessment. A simple approach of using a single-item pain intensity score (e.g. a numeric rating scale, which has strong clinimetric properties) in routine IA consultations, with screening for depression where relevant, appears appropriate. Further research is needed to understand how this could be achieved in different healthcare settings.