The demographic and clinical data of both CAP48 cohorts are globally quite similar to those reported in literature in Caucasians (9–15). In particular, with an annual incidence of 1.4/100000 children and a prevalence of 14/100000 children, this population falls into the range described in Caucasians, even if probably underestimated (16). Indeed, this study based on cohort data overlooks some patients who wouldn’t be missed within the scope of a systematic registry. It is important to note that the clinical characteristics of patients with JIA also depend on geographical and ethnic parameters (17), but the CAP48 cohort comprises mainly Caucasians children (92%). The mean age at onset and diagnosis as well as its distribution are comparable to those observed in the vast Canadian and English naïve cohorts (ReACCH Out and CAPS cohorts) (10, 11). However, the diagnosis delay is here twice higher, and this difference could be partly explained by ignorance of the disease from parents and general practitioners who wait too long before referring to a specialized center. Moreover, it seems that older age at onset and lack of ANA could be associated with that diagnosis delay. This could be interpreted, especially for the negativity for ANA, by a less severe outcome of the disease.
Interestingly, the patients included in this cohort were generally treated in accordance with the last ACR recommendations, with intra-articular corticoids preferentially used in oligoarthritis forms, methotrexate as a first DMARD and biotherapies as a second line of treatment (in the non-systemic forms) (18, 19). As for the systemic forms, usually more challenging to treat, our data confirm that the patients are essentially treated with systemic corticoids alone (19%), methotrexate monotherapy (12%) or biotherapy in monotherapy or combination therapy (69%). Among these, the most used bDMARDs follow ACR guidelines, with a predominance of IL6 and IL1 inhibitors over TNF inhibitors (19).
The remission rates reach 75% at 18 months in naïve patients and improvement was observed in multiple parameters during follow-up (TJC, SJC, physician VAS, patient/parent VAS, CRP and DAS28-CRP). The comparisons with other cohorts are difficult because of the diversity in population, remission criteria and treatment. Notably, Guzman et al (10) reported a remission rate of 70% within 2 years of follow-up and Nordal et al (13) observed a rate of 51% after 8 years of follow-up. Sengler et al (14) mentioned higher remission rates at 1 year in systemic and oligoarthritis forms, as reported in our study, but our data also found high remission rates in RF-negative polyarthritis forms. Furthermore, it is well known that ACR remission criteria defined by Wallace et al (7) are not systematically used in routine, because of their numerous items to evaluate. We thereby compared the follow-up using DAS28, initially created to monitor patients with rheumatoid arthritis, and JADAS10; our results clearly show better concordance of the remission rates between the ACR criteria and JADAS10, compared to those obtained with DAS28. These results strongly confirm the need to study and develop even further this JADAS10 score, created specifically to monitor patients with JIA.
In our study, a good response to treatment is associated with female sex. No other prognosis factors could be identified, probably because of a small cohort size. However, we confirm the higher risk of developing uveitis in presence of ANA, as described (20, 21).
Finally, our study obviously presents some limitations. Our cohort is limited in the number of patients included, especially those with an early diagnosis. The patients included were followed in specialized centers and this could therefore constitute a selection bias by the gathering of potentially more severe patients necessitating more intensive treatment. Moreover, the AJI population is very heterogeneous and leads to analysis in subgroups.
In conclusion, this first cohort study in Belgium permitted to review the distinctive features of the disease. It also allowed to compare epidemiologic and clinical data to other existing cohorts, and to evaluate quality of care in our French-speaking hospitals. Additionally, it highlighted a clear benefit of using JADAS10 to monitor and evaluate remission in JIA, rather than using DAS28, and the necessity to systematically collect some clinical parameters in routine (such as the CHAQ and the patient/parent VAS).
This study was approved by ethic comities of each hospital involved. Informed consent was obtained from each patient and parents.