Incidence of juvenile idiopathic arthritis in the Nordic countries. A population based study with special reference to the validity of the ILAR and EULAR criteria.

Abstract

Incidence rates of juvenile arthritis for areas within the Nordic countries were in accord with previous data. The ILAR criteria present slightly higher incidence rates, with a shorter disease duration for inclusion, compared to the EULAR criteria. Patients in one subgroup in either of the criteria sets do not necessarily belong to the expected subgroup in the other set of criteria; e.g., for juvenile ankylosing spondylitis (EULAR) and enthesitis related arthritis (ILAR). Our epidemiological findings are a reminder to be aware of possible new subgroups in children with juvenile arthritis.