Objective: To evaluate the applicability of the ILAR criteria for classification of childhood arthritis in an outpatient pediatric rheumatology clinic population, and to determine the proportion of children who met standard classification criteria, but failed to meet ILAR criteria for specific arthritides, and therefore became unclassifiable.
Methods: We reviewed the charts of 70 consecutive patients who had arthritis for at least 6 months, and attended the clinic between September and November 1997. Sixty-nine patients were categorized according to one of the traditional classifications [ACR for juvenile rheumatoid arthritis (JRA), European Spondylarthropathy Study Group (ESSG) for spondyloarthropathy, Vancouver Criteria for juvenile psoriatic arthritis (JPsA)], and the ILAR classification system.
Results: Sixty-one patients (88.4%) were classifiable by the ILAR system; 8 others failed to fulfill ILAR criteria for any specific category, and were assigned to the "other arthritis" category. Of the 29 patients with oligoarticular onset JRA, 6 were unclassified, 5 because of exclusions, and one because he fulfilled criteria for 2 categories. Presence of a family history of psoriasis accounted for most of the exclusions in the oligoarthritis and enthesitis related arthritis categories. All patients with polyarticular onset or systemic onset JRA were classified in the corresponding category in the ILAR system. One 9-year-old patient with spondyloarthropathy was reclassified as "other arthritis" because of exclusions. All 6 children with definite JPsA met ILAR criteria for PsA. Of 4 patients with probable JPsA, only 2 met ILAR criteria for PsA, a third was classified as rheumatoid factor negative polyarthritis, and the fourth was classified as "other arthritis" because of exclusions.
Conclusion: The ILAR classification criteria applied to a group of children with chronic arthritis classified by traditional criteria results in reassignment of 11.6% of the patients, predominantly in the oligoarticular group. It will be important to determine the role of the presence of a family history of psoriasis in classifying these patients.