How early is early for JIA? Insights from the infantile-onset juvenile idiopathic arthritis patients of the PERA research group cohort

Abstract

Objective: Juvenile idiopathic arthritis (JIA) is the most common chronic childhood arthritis, with distinct categories based on pathophysiology and clinical manifestations. The age of onset varies by category but is reported to be approximately six years. This study aimed to evaluate the clinical, laboratory and outcome characteristics of patients with infantile-onset JIA. Methods: This multicentre retrospective study included patients with JIA whose symptoms were onset before the age of two. Results: This study included 199 patients with a median age at symptom onset of 17 months and a median age at diagnosis of 20 months. The most common JIA categories were persistent oligoarticular (59.8%), systemic (13.6%) and rheumatoid factor (RF)-negative polyarticular (11.6%). Patients with symptom onset <= 12 months had a significantly higher prevalence of RF-negative polyarticular and systemic JIA, whereas those with onset >12 months had a higher prevalence of persistent oligoarticular JIA. Antinuclear antibody positivity was significantly higher in patients with disease onset >12 months, whereas uveitis development was more common in those with onset <= 12 months. The wrist, hand proximal interphalangeal (PIP) and foot PIP joints were significantly more frequently affected in patients with early-onset disease. At the last visit, 59.8% of the patients were in remission with medication and 18.1% were in remission without medication. Conclusion: This study suggests that patients with infantile-onset JIA exhibit distinct characteristics regarding JIA category, joint involvement and uveitis development, highlighting the need for further research and potential reconsideration of current age thresholds in the JIA classification.