A72: Predicting Progression From Oligoarticular to Polyarticular Juvenile Arthritis

Abstract

Background/Purpose:It has been previously shown that early involvement of wrist and ankle are risk factors for extension of oligoarticular onset juvenile arthritis (oligoJA). Our objective was to determine whether early wrist, ankle, upper limb, or lower limb involvement are risk factors for extension to a polyarticular course in a cohort of paediatric patients with oligoJA.Methods:This is a retrospective cohort study of children with oligoJA presenting to paediatric rheumatology clinics at the two Canadian paediatric centres from 1981 to 2010. OligoJA was defined as ≤4 joints at the first and 6 month visits. Risk factors for extension from oligoJA to polyarthritis (>5 joints) by 2 and 5 years after diagnosis were modelled using logistic regression while controlling for sex, ever having used DMARDs, or intraarticular corticosteroid injections. Time to extension was assessed using Cox proportional hazard analysis.Results:420 patients met eligibility criteria. 56% were female. The median time from disease onset to diagnosis was 136 days (IQR 55.5 days, 365.0 days); 15 patients in the logistic regression models extended by 2 years (n=280, of which 5.4% extended) and 27 by 5 years (n=339, of which 8.0% extended). At 2 years after diagnosis the odds of extension was 6.1 times higher (95% CI 1.9, 24.3) in those with initial wrist involvement than in those without, and at 5 years it was 3.1 times higher (95% CI 1.0, 8.0). The OR of extension in those with initial upper limb involvement versus those without was 7.0 (95% C.I. 2.3, 21.6) at 2 years and 6.3 (95% C.I. 2.5, 15.8) at 5 years. Cox proportional hazard modelling showed a HR of 2.3 (95% CI 1.2, 4.5) in patients with upper limb involvement compared to without upper limb involvement indicating that extension was 2.3 times more likely to occur in the former group. The likelihood ratio was 68.7, p value < 0.0001, degrees of freedom (d.f) = 4, and events per variable = 9.8.Conclusion:This study independently confirms previous published findings that wrist and upper limb arthritis in the first 6 months after diagnosis of oligoJA is a risk factor for extension. Unlike previous reports, we did not find an increased probability of extension in patients with early ankle arthritis. Patients with upper limb arthritis in the first 6 months after diagnosis were more likely to extend sooner than those without early upper limb arthritis.