Juvenile idiopathic arthritis is relatively prevalent among school-aged children in Brazil, affecting 196 children for every 100.000, a population-based study reveals.

The study, “Prevalence of juvenile idiopathic arthritis in schoolchildren from the city of São Paulo, the largest city in Latin America,” was published in the journal Advances in Rheumatology.

Juvenile idiopathic arthritis is the most prevalent chronic rheumatic disease among children and adolescents. It is characterized by chronic inflammation of the joints that, if left untreated, can lead to progressive and destructive arthritis.

The prevalence of this disease has been found to be quite variable among different populations, ranging between 3.83 and 400 cases for every 100,000 children. This variability is believed to be, at least in part, due to genetic factors and changes in the mechanisms of genetic regulation (epigenetics).

Brazilian researchers evaluated the prevalence of juvenile idiopathic arthritis in São Paulo, one of the most populous cities in the world.

The team asked parents and caregivers of children and adolescents (between 1 and 16 years old) from 12 private schools in São Paulo to respond to the Early Diagnosis of Arthritis 12 (EDA-12) questionnaire.

This is a validated screening tool that is composed of 12 simple questions about current and past signs and symptoms of juvenile idiopathic arthritis, such as joint pain or swelling, deformities, fever and rash, as well as patterns of daily activities. One point is granted for every positive response, meaning that the EDA-12 will range from 0 to a maximum of 12 points.

The team collected a total of 5,710 questionnaires, of which 108 (1.89%) had scores of 5 or more points.

The parents of these students were called for an appointment to review their child’s medical history, while the children underwent a physical examination at school. After this process was completed, 10 children (five girls and five boys) were confirmed as meeting the diagnostic criteria for juvenile idiopathic arthritis.

These children were 4 to 13 years old and the numbers of tender or painful joints varied from one to 10. Seven of these children were found to have oligoarticular arthritis, while three had polyarticular disease. All reported  they already were in follow-up with pediatric rheumatologists and ophthalmologists.

These findings demonstrate that juvenile idiopathic arthritis affects 0.196% of children aged 1 to 16 years, with an estimated prevalence of 196 cases for every 100,000 children and adolescents in Brazil.

“This prevalence is within the range observed in similar studies conducted in other countries,”  the researchers wrote.

“[T]he EDA-12 items questionnaire proved to be a useful tool in screening suspected cases of chronic arthropathy,” they said.