Characteristics and Outcomes of Children with Enthesitis in Juvenile Idiopathic Arthritis

Abstract

Objectives - To describe the prevalence, associated characteristics, and course of enthesitis in a inception cohort of children with juvenile idiopathic arthritis (JIA) and to estimate the impact of enthesitis on patient reported outcomes (PROs) in these children, irrespective of their JIA category. Methods - Canadian children newly diagnosed with JIA between 2005 and 2010 followed for up to 5 years in the Research in Arthritis in Canadian Children Emphasizing Outcomes (ReACCh-Out) cohort were studied. The presence of entheseal tenderness by physician examination at 33 sites shown on a homunculus, Juvenile Arthritis Quality of life Questionnaire (JAQQ), Quality of My Life questionnaire (QoML), Childhood Health Assessment Questionnaire (CHAQ), and a pain severity visual analogue scale (VAS) were completed at enrolment, every six months for 2 years, and then yearly up to 5 years. Analyses consisted of descriptive statistics, linear mixed models for longitudinal data, and ANCOVA. Results - Of 1406 patients, 219 (16%) had enthesitis and, of those with enthesitis, 141 (64%) were classified as having enthesitis-related arthritis (ERA). Children with enthesitis were more often older (10.7 versus 7.5 years), male (57% versus 31%), and with polyarthritis (57% versus 41%) and sacroiliac involvement (30% versus 4%). Entheseal tenderness was most frequent at the calcaneal plantar fascial insertion (39%), Achilles tendon insertion (31%), and tibial tuberosity (30%). The mean number of tender entheseal sites decreased in parallel with active joint counts. There was no difference in active joint counts over time in children with or without enthesitis (p = 0.73). A total of 1371 patients reported at least one PRO. These patients were followed for a median of 35.3 months. After adjusting for JIA category and covariates, children with enthesitis reported higher JAQQ (mean raw score 2.71 vs 2.16; adjusted difference 0.41 points; 95% CI 0.22, 0.59), higher CHAQ (0.47 vs 0.31; 0.14 points; 0.07, 0.22), higher pain (3.01 vs 1.68; 0.94 points; 0.64, 1.25) and lower QoML (7.02 vs 8.23; -0.80 points; 95% CI -1.09, -0.51) scores than children without enthesitis. These differences persisted up to five years after diagnosis. Conclusion - Enthesitis was observed in 16% of patients with JIA, but only two thirds were categorized as having ERA. Contrary to expectations, most children with enthesitis had polyarticular involvement. The course of enthesitis paralleled the course of active joint counts. Children with enthesitis, regardless of JIA category, report worse PROs than those without enthesitis. Physicians should assess for enthesitis in all children with JIA and, if present, make it a treatment target. Enthesitis should be considered as criterion for classification and assessment of treatment response in JIA.