Background: Musculoskeletal pain significantly affects people with rheumatoid arthritis (RA), impacting their functional ability. Prolonged inflammatory processes may sensitise the nervous system and the neurons innervating peripheral joints, leading to increased activity in the central nervous system (CNS) and disproportionate and widespread pain. Individuals with RA often report difficulties undertaking everyday tasks. Pain makes it unpleasant to do everyday activities and is associated with disability. The association between pain and disability might not be driven by pain intensity alone. It is important to understand the extent to which augmented central pain processing influences disability in RA.

Objectives: It is hypothesised that augmented central pain processing will be associated with disability in individuals with RA.

Methods: As part of the Central Aspects of Pain in RA (CAP-RA) study, adults with RA and pain ≥4/10 were recruited from Nottinghamshire hospitals and the Investigating Musculoskeletal Health and Wellbeing Cohort. Augmented central pain processing was assessed using quantitative sensory testing (QST: Pressure Pain detection Threshold [PPT], Temporal Summation of Pain [TSP], and Conditioned Pain Modulation [CPM]), the Central Aspects of Pain (CAP), and Central Sensitisation Inventory Short form (CSI-9) questionnaires. The Health Assessment Questionnaire (HAQ) assessed disability. Visual Analog Scales for pain now, average pain and strongest pain over the past 4 weeks were combined into a single ‘combined pain’ score, normalised into a 0-10 score. Inflammation was assessed using the Disease Activity Score 28, C-reactive protein (CRP), and Backhaus-7 Greyscale and Power Doppler ultrasound, scored using EULAR-OMERACT criteria. The Bristol Rheumatoid Arthritis Fatigue scale (BRAF) assessed fatigue. Assessments were completed at baseline and 12 weeks. Spearman Correlations and linear regressions assessed associations (β (95% CI) p-value), with adjusted R ² used to quantify the percentage variance explained. Data are presented as mean ± SD or median (IQR).

Results: At baseline, 194 people completed assessments, with a mean age of 65.8±11.3 years, 74% were female, a BMI of 29.2±5.8 kg/m2, a DAS28-CRP of 4.4±1.2, CAP score of 9.0 (1.0, 11.0)/16 a CSI-9 score of 21.0 (16.3, 26.0)/36, a HAQ score of 1.6 (1.1, 2.0)/3, and with combined pain of 6.7 (5.0, 8.0)/10. At 12 weeks, the CAP score was 7.0 (5.0, 11.0), the CSI-9 was 19.5 (16.0, 25.0), the HAQ was 1.6 (1.1, 2.0), and the combined pain score was 6.3 (4.0, 7.7). Baseline augmented central pain measures (CAP, CSI-9) were significantly associated with disability (Table 1), whilst QST measures were not. In multivariable regression models, CAP, but not CSI-9, remained significantly associated with HAQ (Table 1). No independent predictors were significantly associated with 12-week HAQ scores (Table 1). Changes in CAP and CSI from baseline to 12 weeks were associated with changes HAQ (Table 1).

Conclusions: Augmented central pain processing (CAP, CSI-9) might influence disability (HAQ), beyond the effects of pain severity. Longitudinally, measures of augmented pain processing were not associated with disability, but this could reflect the minimal change in HAQ score over 12 weeks. Changes in CAP and CSI-9 were associated with changes in HAQ, suggesting that objective measures of augmented central pain processing may contribute to disability. Interventions targeting improved physical functioning should consider augmented central pain processing alongside pain severity for optimal rehabilitation outcomes.

REFERENCES: NIL.

Acknowledgments: NIL.

Disclosure of Interests: Charlotte Ainsworth: None declared, Daniel McWilliams Pfizer, Eli Lilly and Company, Orion Pharma, UCB, GSK., David Walsh Pfizer, Eli Lilly and Company, Orion Pharma, UCB, GSK., Vasileios Georgopoulos: None declared, Stephanie Smith: None declared.