Introduction: Methotrexate (MTX) is the drug of choice for juvenile idiopathic arthritis. Its clinical efficacy is limited due to the development of adverse effects (AEs). Patients and methods: A retrospective observational study was conducted on the AEs associated with MTX therapy in children diagnosed with juvenile idiopathic arthritis followed-up in a tertiary hospital between 2008 and 2016. Results: The study included a total of 107 patients, of whom 71 (66.3%) were girls (66.3%). The median age at diagnosis was 6.4 years (IQR 3.1-12.4), with a median follow-up of 45.7 months (IQR 28.8-92.4). There were 48 patients (44.9%) with oligoarthritis, and 26 children (24.3%) with rheumatoid-factor negative polyarthritis. Of these, 52/107 (48.6%) developed AEs, with the most frequent being gastrointestinal symptoms (35.6%) and behavioural problems (35.6%). An age older than 6 years at the beginning of therapy increased the risk of developing AEs, both in the univariate (OR=3.5; 95% CI: 1.5-7.3) and multivariate (12% increase per year) analyses. The doses used, administration route, or International League of Associations for Rheumatology (ILAR) classification, were not associated with the development of AEs. Twenty children required a dosage or route of administration modification, which resolved the AE in 11 (55%) cases. MTX was interrupted due to the development of AEs in 37/107 patients (34.6%), mainly due to increased plasma transaminases (n = 14, 37.8%), gastrointestinal symptoms (n = 9, 24.3%) and behavioural problems (n = 6, 16.3%). Conclusions: MTX is the therapy of choice for patients with juvenile idiopathic arthritis, but 50% of the children develop some form of AE. Although the AEs are not severe, they lead to interruption of therapy in 35% of the children. (c) 2019 Asociacion Espanola de Pediatria. Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction: Synovial fluid (SF) analysis is an important tool for the diagnosis of patients with juvenile idiopathic arthritis (JIA). Patients and methods: A retrospective analysis was carried out of cytological features of SF samples obtained from patients with JIA during the period 2008-2016. Results: A total of 102 SF samples from 59 patients were analysed. JIA was more common in females (66%). The most frequent form was persistent oligoarticular JIA (52.5%). The median age at onset was 5 years (IQR 2.4-11.8). SF usually showed an inflammatory pattern (median white blood cells count 11,757/mm(3); IQR 4,543-18,800), with a predominance of polymorphonuclear (PMN) cells (61%; IQR 30-75). Eight patients (14%) had white blood cells counts of less than 2000 cells/mm(3), with predominance of mononuclear cells (80%), whereas 3 patients (5%) had white blood cells counts higher than 50,000 cells/mm(3), with a predominance of PMN cells (90%). Synovial white blood cells count did not show significant differences among the different forms of JIA. The median synovial white blood cells count in ANA-positive patients was 20% lower than in ANA-negative (9,340 vs. 11,600/mm(3); P = .23). The proportion of PMN increased with increasing levels of ESR (P < .001) and/or CRP (P = .03). No significant correlation was found between JADAS-10 and synovial white blood cells count (P = .4). SF obtained from different joints in simultaneous arthrocentesis showed a significant correlation P = .001). Conclusion: SF from JIA patients usually had inflammatory characteristics, although 19% of the patients showed white blood cells counts below 2000 cells/mm(3) or higher than 50,000 cells/mm(3). SF cell count was non-significantly lower in ANA-positive patients, and the proportion of PMN increased with increasing levels of ESR/CRP. (C) 2019 Published by Elsevier Espana, S.L.U.