A better understanding of juvenile idiopathic arthritis with classification criteria.

Juvenile idiopathic arthritis, JIA, is a novel rheumatic disease in childhood introduced by the International League of Associations for Rheumatology. It is defined as a chronic, inflammatory disorder of unknown etiology, which is classified into seven categories; systemic-onset type, persistent and extended oligoarthritis, polyarthritis with rheumatoid factor negative, polyarthritis with rheumatoid factor positive, psoriatic arthritis, enthesitis-related arthritis and undifferentiated arthritis. As each category of JIA has different features in clinical phenotypes, precise subtyping is required for research and management. However, some modifications to the criteria might be helpful for getting better answers in diagnosis because of ethnical difference in prevalence and subtype distribution. Actually in Japanese population, a unique subset "B27-negative polyenthesitis" termed by Shichikawa should be included in enthesitis-related arthritis of JIA as a different type of enthesitis from B27-positive counterpart of spondyloarthritis in adulthood. Deep insights into the classification criteria will be needed for the better understanding of JIA.