Ab0135 Relating Peripheral Joint Inflammation and Pain in Rheumatoid Arthritis: A Musculoskeletal Ultrasound Study

Background: Rheumatoid arthritis (RA) is a chronic autoimmune disorder associated with significant pain and subsequent poor quality of life. Due to the conventional belief that the primary pain mechanism in Rheumatoid Arthritis (RA) is nociceptive and related to joint inflammation, physicians have long considered pain an indicator of ongoing inflammation. However, even with the effective use of anti-inflammatory drugs, up to 50% of patients in remission continue to experience pain. Thus, alternative pain mechanisms may exist. Musculoskeletal ultrasound (MSUS) is a sensitive tool to identify joint inflammatory changes. Objectives: In this study, MSUS was employed as a measure of nociceptive pain to investigate the relationship between joint inflammation and pain in RA. The goal was to quantify the contribution of inflammatory nociceptive mechanisms in explaining the totality of pain in RA. Methods: This study was a secondary analysis of a prospective study (Naredo et al., 2008) of RA patients who met the 1987 American College of Rheumatology criteria. The study was conducted on 367 participants starting treatment with a tumour necrosis factor-alpha (TNFα) blocking agent. The participants underwent assessments, including clinical, laboratory, MSUS, pain VAS 100mm, and DAS28 at baseline and after 12 months of treatment. MSUS examination included 86 sites in 28 joints, and synovial fluid (SF), synovial hypertrophy (SH), and Power Doppler (PD) signals were scored. MSUS metrics scores were graded semi-quantitatively on a scale of 0–3 (0 " absent; 1 " mild; 2 " moderate; 3 " marked). The relationship between pain VAS and MSUS metrics in RA was examined using appropriate correlations and linear regression models cross-sectionally at baseline and longitudinally. In a linear regression model, the longitudinal analysis assessed the change between baseline and 12 months in the MSUS metrics as explanatory variables for change in pain VAS. Results: A moderate significant correlation with a minor effect size was observed between pain VAS and MSUS metrics, namely PD, SF and SH at baseline (r = 0.154, p = 0.003; r = 0.123, p = 0.018; r = 0.111, p = 0.034, respectively). Furthermore, a strong statistically significant correlation with a small effect size was observed between longitudinal changes in pain VAS and MSUS metrics, namely PD, SF and SH (r = 0.197, p Conclusion: The findings indicate that the MSUS metrics of joint inflammation only accounted for a minor portion of pain experienced by patients with RA. These findings suggest that nociceptive pain mechanisms do not predominate as classically considered and that other pain mechanisms, such as nociplastic pain, require elucidation. REFERENCES: 1 Naredo, E., Möller, I., Cruz, A., Carmona, L. and Garrido, J., 2008. Power Doppler ultrasonographic monitoring of response to anti–tumor necrosis factor therapy in patients with rheumatoid arthritis. Arthritis & Rheumatism: Official Journal of the American College of Rheumatology, 58(8), pp.2248-2256. Acknowledgements: NIL. Disclosure of Interests: None declared.