FRI0061 THE CONTRIBUTION OF TENOSYNOVITIS OF SMALL JOINTS TO THE SYMPTOM MORNING STIFFNESS IN PATIENTS PRESENTING WITH UNDIFFERENTIATED AND RHEUMATOID ARTHRITIS

Background Morning stiffness (MS) is characteristic of Rheumatoid Arthritis (RA) that is associated with functional disability. Despite the known parallel in the circadian rhythm of MS and that of several hormones and pro-inflammatory cytokines in the systemic circulation, it is insufficiently known to what extent local inflammatory processes contribute to this symptom. The correlation between MS and the number of swollen joints is relatively weak but may be underestimated by insufficient sensitivity in measuring local inflammation. MRI is more sensitive in detecting local inflammation. Furthermore, MRI-detected tenosynovitis of small joints is increasingly recognized as early feature of RA which is also associated with functional impairments. Recently it was proposed that this may contribute to MS. Objectives We assessed the relationship between MS and MRI-detected inflammation and tenosynovitis in particular. Methods 286 consecutive patients newly presenting with undifferentiated and rheumatoid arthritis underwent contrast-enhanced 1.5T-MRI of (2-5)MCP-, (1-5)MTP-, and wrist-joints. Scans were scored for tenosynovitis according to Haavardsholm and for synovitis, osteitis conform the RAMRIS-method. MS was dichotomized as>60 minutes. Associations between MS and tenosynovitis/synovitis were tested with logistic regression and the presence of a biologic interaction was assessed categorically (solitary or simultaneous presence of synovitis/tenosynovitis). Results MS was present in 40% of patients. Tenosynovitis was more often present in patients with MS than without MS (80% versus 65%), OR 2.11 (95%CI 1.21;3.69). Also synovitis was more often present in patients with MS (58% versus 44%), OR 1.83 (1.12;2.96). In categorized analyses the largest association was found for concurrent synovitis and tenosynovitis OR 2.43 (1.30;4.54); whereas single presence of synovitis was not associated (OR 0.85 (0.21;3.47)). The variance explained in all analyses on morning stiffness was small, ranging 3-6%. Conclusion Tenosynovitis, and simultaneous presence of tenosynovitis and synovitis in particular, was associated with MS. However, effect sizes suggested that the contribution of local inflammation to this symptom is rather limited. Acknowledgement E.C. Newsum and W.P. Nieuwenhuis are acknowledged for scoring MRI-scans. Disclosure of Interests Aleid Boer: None declared, Debbie Boeters: None declared, Ellis Niemantsverdriet: None declared, Annette van der Helm - van Mil Grant/research support from: The research leading to these results has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Starting grant, agreement No 714312) and from the Dutch Arthritis Foundation. The funding source had no role in the design and conduct of the study.