Background/Purpose: Advanced imaging modalities have shown that not only joints but also bones and tendon sheaths can be inflamed at diagnosis of rheumatoid arthritis. We aimed to better understand the time order in which the inflamed tissues respond to DMARD-treatment and whether this differs between ACPA-subgroups.

Methods: 216 consecutive patients presenting with undifferentiated or rheumatoid arthritis, who received DMARD-treatment, were studied. 1.5T contrast-enhanced hand and foot MRIs were performed before treatment and after 4, 12 and 24-months. Cross-lagged models evaluated the influence of two time-patterns: a simultaneous pattern (“change in one inflammatory feature associated with change in another feature”) and a subsequent pattern (“change in one inflammatory feature preceded change in another feature”). ACPA-stratification was performed.

Results: All pairs of inflammatory features decreased simultaneously in all time-intervals (0–4/4–12/12–24m; p< 0.05). Moreover, time orders were identified: synovitis decrease preceded tenosynovitis decrease (0-4m- >4-12m; p=0.02 & 4-12m- >12-24m; p=0.03). Similar results were obtained in both ACPA-subgroups. Additionally, in ACPA-positive but not ACPA-negative patients, synovitis decrease preceded osteitis decrease (4-12m- >12-24m; p=0.002).

Conclusion: This study increased the understanding of the response to treatment on tissue level. Additional to simultaneous decrease of inflammation, synovitis decrease preceded tenosynovitis decrease. Differences in time order of inflammation decrease between ACPA-subgroups suggest differences in underlying inflammatory pathways.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/chronological-order-of-decrease-of-synovitis-osteitis-and-tenosynovitis-in-early-arthritis-patients-receiving-first-dmard-treatment/