Background Adverse drug reactions (ADRs) are the sixth leading causes of death worldwide; monitoring them is fundamental, especially in patients with disorders like chronic rheumatic diseases (CRDs). The study aimed to describe the ADRs investigating their severity and associated factors and resulting interventions in pediatric patients with CRDs. Methods A retrospective, descriptive and analytical study was conducted on a cohort of children and adolescents with juvenile idiopathic arthritis (JIA), juvenile systemic lupus erythematosus (JSLE) and juvenile dermatomyositis (JDM). The study evaluated medical records of the patients to determine the causality and the management of ADRs. In order to investigate the risk factors that would increase the risk of ADRs, a logistic regression model was carried out on a group of patients treated with the main used drug. Results We observed 949 ADRs in 547 patients studied. Methotrexate (MTX) was the most frequently used medication and also the cause of the most ADRs, which occurred in 63.3% of patients, followed by glucocorticoids (GCs). Comparing synthetic disease-modifying anti-rheumatic drugs (sDMARDs) vs biologic disease-modifying anti-rheumatic drugs (bDMARDs), the ADRs attributed to the former were by far higher than the latter. In general, the severity of ADRs was moderate and manageable. Drug withdrawal occurred in almost a quarter of the cases. In terms of risk factors, most patients who experienced ADRs due to MTX, were 16 years old or younger and received MTX in doses equal or higher than 0.6 mg/kg/week. Patients with JIA and JDM had a lower risk of ADRs than patients with JSLE. In the multiple regression model, the use of GCs for over 6 months led to an increase of 0.5% in the number of ADRs. Conclusions Although the ADRs highly likely affect a wide range of children and adolescents with CRDs they were considered moderate and manageable cases mostly. However, triggers of ADRs need further investigations.

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BACKGROUND Polyarteritis Nodosa is a necrotizing vasculitis that affects especially medium vessels. It can be a challenge in children due to atypical symptoms and long time up to diagnosis and treatment. CASE REPORT JSS, 11 years old girl, previously healthy, without familial history of autoimmune diseases, started one year ago daily fever around 39° for 6 months with no focus and spontaneous resolution. After 2 months of symptoms onset, she presented edema on the lower limbs with painful nodules and difficulty to step on the floor. She complained about weight loss (10 kilos in one year), anemia and high acute phase reactants. Initial infectious and oncologic work up was carried out and was negative. She presented all autoantibodies, including ANCA, negative, negative Mantoux test, normal dosage of muscle enzymes, and renal and hepatic function and normal echocardiogram. She presented anemia, discrete thrombocytosis and persistently elevated acute phase reactants. Ophthalmologic evaluation showed no alterations. MRI of the lower limbs was performed, with inflammatory perivascular signals on the fibular, soleal and tibial muscles with intraosseous nodulations. Biopsy on lower limb was requested and the results showed polyarteritis nodosa, with immunofluorescence negative. Immunosuppressive therapy with corticosteroids and azathioprine was started. CONCLUSION As presented in this case, PAN in children can take long time to diagnosis due to their varied clinical manifestation. The diagnosis is performed by clinical and histopathological findings