Lay Summary

Different measures of pain produce different patterns of pain progression, and these are differentially related to mental health. Knee pain trajectories determine treatment choices for knee pain itself and related mental illnesses.

Background

Chronic pain associated with knee osteoarthritis is the major source of mental distress with pain progression linked to higher rates of anxiety and depression leading to early disability retirement. Optimism, as a personality trait, has been found to mitigate the impact of chronic pain on mental health. Different behavioural and symptomatic pain mechanisms could have different mental outcomes and be affected by the level of optimism. Previous studies defining pain trajectories have all used a single measure of pain that failed to examine the impact of different pain mechanisms to predict different mental disorders.

Methods

Data for this study were taken from Knee Pain In the Community (KPIC) cohort in Nottinghamshire. A total of 2141 older age (baseline mean 62.41 years) participants met the inclusion criteria. Behavioural and neuropathic-like pain were measured using Intermittent and Constant Osteoarthritis Pain (ICOAP) and the painDETECT, respectively, across 3 waves (the baseline, 1- and 3-year follow-ups). The Hospital Anxiety and Depression Scale (HADS) was used to measure pain-induced anxiety and depression. Life-Orientation Test was used to measure optimism. To ascertain the clinical utility of pain progression, the pain trajectory models were adjusted for the medication used as time-varying covariates.

Results

Latent class growth analysis identified 6 trajectories using ICOAP subscales (High, Low, Moderate Worsening, Moderate Recovering, Worsening, and Recovering), and 4 trajectories using painDETECT (High, Low, Worsening, and Recovering). Random effect panel regression analyses showed that anxiety and depression were differently associated with pain trajectories. Anxiety had a pattern of decrease and depression was stable over time as people experience chronic pain. Older people had a lower level of anxiety but higher depression scores. Neuropathic-like pain had a greater impact on depression than anxiety. People with high optimism had lower pain experience throughout all pain trajectories. High optimism was also associated with lower anxiety and depression.

Conclusion

Different measures of pain produce different patterns of pain progression, and these are differentially related to mental distress. Anxiety is linked to trajectories of pain based on the impact of pain on behaviour and not pain symptoms. Thus, managing pain’s behavioural impact is more central to understanding the link between anxiety and behaviour than managing pain symptoms. These findings support more in-depth questioning about the type of pain, its link to mental health, and its progression in clinical practice.