New Provisional Classification of Juvenile Idiopathic Arthritis Applying Rheumatoid Factor and Antinuclear Antibody

ABSTRACT

OBJECTIVE: Previous classification systems for juvenile idiopathic arthritis (JIA) were based on the number of joints involved and did not categorize homogenous disease entities. Therefore, JIA patients were reclassified retrospectively by applying rheumatoid factor (RF) and antinuclear antibody (ANA), which have been proven to constitute a homogenous disease entity. METHODS: The medical records of JIA patients were investigated retrospectively and reclassified into six categories using the new provisional classification. The nomenclature was based on Dr. Martini's proposal in the 23rd European Paediatric Rheumatology Congress (2016) at Genoa, Italy. New categories included systemic JIA (sJIA), RF-positive JIA (RF-JIA), early-onset ANA-positive JIA (eoANA-JIA), enthesitis/spondylitis-related JIA (ESR-JIA), “other JIA”, and “unclassified JIA”. RESULTS: Of a total of 262 JIA patients, 71 (27.1%) were reclassified as sJIA, 31 (11.8%) as RF-JIA, 22 (8.4%) as eoANA-JIA, 63 (24.0%) as ESR-JIA, 65 (24.8%) as “other JIA”, and 10 (3.8%) as “unclassified JIA”. A comparison of RF-JIA, eoANA-JIA, and ESR-JIA revealed significant differences in the gender ratio, age of disease onset, and the cumulative number and type of joints involved among the three groups. “Other JIA” comprised a significant proportion (24.8%) and warrants the need for further classification. The characteristics of the RF-positive patients were comparable to those of the anti-cyclic citrullinated peptide antibody-positive patients. The ANA positivity was lower (28.2%) than that in Western studies but showed similar clinical features. CONCLUSION: This is the first study applying RF and ANA to classify JIA without considering the joint counts. The six new categories include sJIA, RF-JIA, eoANA-JIA, ESR-JIA, “other JIA,” and “unclassified JIA”.