Background/Purpose: Reduced cardiorespiratory fitness (CRF) has previously been found in children with juvenile idiopathic arthritis (JIA) compared to healthy children. However, little is known about CRF in JIA patients treated in the biologic era. The aims were to compare CRF in JIA patients who have had access to biological treatment from disease onset with controls, and to study associations between CRF and measures of disease activity in patients.  

Methods: Patients with persistent oligoarthrtitis or polyarticular disease were recruited consecutively at Oslo University Hospital. Age- and sex-matched controls were selected randomly from the Norwegian Population Registry. In all participants, CRF was directly measured as peak oxygen uptake (VO_2peak) during a continuous graded exercise test on a treadmill until exhaustion. Present pain and pain and fatigue the last week were assessed by a Numeric Rating Scale (NRS). Puberty was self-rated using the Tanner Scale. In patients, the Juvenile Arthritis Disease Activity Score 71 (JADAS 71) and the Childhood Health Assessment Questionnaire (CHAQ) were used to measure disease activity and functional disability, respectively. Differences between groups were tested with paired t-tests, or Wilcoxon rank test and correlations with Pearson or Spearman’s rho correlation coefficients.  

Results: Fifty-nine patients (50 girls, 9 boys) with JIA, 30 with persistent oligo arthritis and 29 with polyarticular disease (extended oligoarthitis and polyarticular RF +/-) aged 10-16 years and 59 controls were included. All patients had been encouraged to stay physically active with no general restrictions regarding physical activity. Twenty-five (42.4 %) patients used biological drugs. No differences were found in VO_2peak (mL/kg/min) in patients vs controls; 45.1 ± 8.5 vs 46.5 ± 8.5, (p=0.38). Furthermore, there were no differences in VO_2peak (mL/kg/min) in patients with persistent oligoarthritis vs polyarthritis; 45.0 ± 7.6 vs 45.3 ± 9.4, (p= 0.87) or in patients with active disease (n=39) vs patients in remission (n=20) (46.4 ± 9.7 vs 44.5 ± 7.9, p=0.43). In patients, there were no correlations between VO_2peak and JADAS 71, number of active joints in the lower extremities, use of medication, use of biological medication, disease duration, CHAQ, present pain  and fatigue (all r<-0.3, p=NS). However, VO_2peak correlated weakly with pain last week (r= -0.28, p=0.03).   

Conclusion: CRF in JIA patients treated in the biological era is comparable to controls, and also comparable between patients with persistent oligo arthritis and polyarticular disease. Even if less than half the patients used biological drugs, the positive results may be explained by advances in multidisciplinary treatment including less limitations regarding physical activity.