The dual role of body mass index on Juvenile Idiopathic Arthritis course: a pediatric experience

: Despite the well-known role of obesity as risk factor for Juvenile Idiopathic Arthritis (JIA) severity, emerging but limited evidence suggested a similar role for underweight. We investigated the role of body mass index (BMI) across its full spectrum in a cohort of children with JIA.We retrospectively studied 113 children with JIA classified according to the International League of Association for Rheumatology (ILAR) criteria attending our Rheumatology Clinic. The patients underwent a comprehensive evaluation including both clinical and biochemical assessments. According to BMI Z-score, the cohort was divided into five groups as underweight, normal weight, overweight (OW), obesity (OB), and severe OB. Disease activity was calculated by Juvenile Arthritis Disease Activity Score 10 (JADAS-10) joint reduced count and relapses were defined according to Wallace criteria.The mean age of the cohort was 7.43 ± 4.03 years. The prevalence of underweight, normal weight, OW, OB, and severe OB was 7.2%, 54.1%, 10.8%, 17.1%, and 10.8%, respectively. Significant higher ferritin levels and erythrocyte sedimentation rate values were found in patients with severe OB and underweight compared to subjects belonging to normal weight, OW, and OB groups. A greater JADAS-10 score was observed in underweight patients and in those with severe OB than other groups. The relapse rate was higher in patients with severe OB and underweight compared to other groups.          Conclusions: Both underweight and OB might negatively affect JIA course. Weight control is fundamental in children with JIA to avoid a more unfavourable course of the disease. What is Known: • Obesity represents a well-known risk factor for JIA severity. • The role of underweight in children with JIA is still poorly explored. What is New: • As observed in children with obesity, underweight young patients with JIA seem to experience a more severe JIA course. • Healthy lifestyle promotion in children with JIA is a crucial step in the management of the disease.