Ankle arthritis predicts polyarticular disease course and unfavourable outcome in children with juvenile idiopathic arthritis.

Objective To evaluate the occurrence, clinical characteristics and prognostic factors associated with ankle arthritis in children with juvenile idiopathic arthritis (JIA). Methods 440 children with JIA were followed for eight years in a prospective Nordic population-based cohort study. Data on remission was available for 427 of these children. Occurrence of clinically assessed ankle arthritis was analysed in relation to JIA category, clinical characteristics and remission data eight years after disease onset. Results In 440 children with JIA, 251 (57%) experienced ankle arthritis during the first eight years of disease. Ankle arthritis was least common in the persistent oligoarticular category (25%) and most common in children with extended oligoarticular (83%) and polyarticular RF-negative (85%) JIA. Children who developed ankle arthritis during the first year of disease were younger at disease onset (median age 4.9 (IQR 2.1-8.8) vs. 6.6 (IQR 2.8-10.1) years, p<0.003) and had more cumulative affected joints at 8-year follow-up (median involved joints 10 (IQR 6-16) vs. 3 (IQR 2-9), p<0.001). The odds ratio for not achieving remission eight years after disease onset, if the ankle joint was involved during the first year of disease was 2.0 (95 %.0, p<0.001). Hind-, mid- and forefoot involvements were more common compared to patients without ankle arthritis. Conclusion In this Nordic population-based 8-year follow-up study, occurrence of ankle arthritis during the first year was associated with an unfavourable disease outcome. We suggest that ankle arthritis should be recognised in the assessment of prognosis and choice of treatment strategy in JIA.