Background/Purpose: Tarsitis is defined as inflammation of intertarsal joints, overlying tendons, entheses and soft tissue and is often under-recognized particularly in pediatrics. Our aim is to characterize clinical features, imagin findings, and treatment response of tarsitis in juvenile idiopathic arthritis (JIA).

Methods: Retrospective multicenter cohort (2014-–2025) included JIA patients with tarsitis, Patients were grouped as isolated tarsitis vs tarsitis with additional joint involvement. Primary outcomes were treatment failure rate to first line DMARDS.

Results: Thirty-nine patients were included (69% female); 11 had isolated tarsitis and 28 had additional joint involvement. Mean age at tarsitis onset was 7.1 years. Polyarticular JIA (51%) and ERA (23%) were the most frequent categories. Most patients initiated MTX (87%); the majority (76.5%) required escalation to biologics. First-line anti-TNF therapy achieved high rates of remission. Compared with other involved joints, tarsitis showed greater MTX non-response with P value < 0.032 ,and odds ratio 4.44 (95% CI 1.17–16.92). Median time to inactive tarsitis was 8–9 months

Conclusion: This multicenter cohort demonstrates that tarsitis represents a distinct and challenging manifestation of JIA, often presenting early, with female predominance, frequent ANA positivity, and a high rate of MTX resistance compared with other joints. Our results, together with the limited literature, suggest that tarsitis should be recognized as a high-risk feature warranting early escalation to biologic therapy. Current ACR/EULAR guidelines do not specifically address tarsal involvement, and our data provides a rationale for its inclusion in future treatment recommendations

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/tarsitis-in-juvenile-idiopathic-arthritis-clinical-characteristics-imaging-features-and-treatment-response-a-multicenter-retrospective-study/