The Number of Affected Joints Is Still a Distinguishing Criterion for Classifying Patients With Juvenile Idiopathic Arthritis.

Objective: Juvenile idiopathic arthritis is a heterogeneous group of chronic childhood arthritis. We planned to classify patients with oligoarticular, rheumatoid factor (RF)-negative polyarticular and undifferentiated groups according to the International League of Associations for Rheumatology criteria, most of them in other or undifferentiated groups according to the new proposed PRINTO (Pediatric Rheumatology International Trials Organization) criteria, into more homogeneous groups according to their clinical and laboratory findings.

Methods: Two hundred three patients with oligoarticular, RF-negative polyarticular and undifferentiated juvenile idiopathic arthritis were included in the study. Sixteen clinical and laboratory variables were evaluated using TwoStep Cluster analysis. Clinical and laboratory characteristics of the resulting clusters were then compared with each other.

Results: Two clusters were generated as the result of cluster analysis. Cluster 1 had 138 (68%) and cluster 2 had 65 (32%) patients. The main indicators differentiating 2 clusters were wrist and elbow involvement and the number of affected joints. The number of affected joints was 2 (1-8) and 6 (1-26) in cluster 1 and cluster 2 (p < 0.001). Wrist and shoulder involvements were seen only in cluster 2 (p < 0.001). Ankle, elbow, small joint, and temporomandibular joint involvements were higher in cluster 2. Corticosteroids, disease-modifying antirheumatic drugs, and biologics were used at higher rates, and remissions at the 12th month and last visit were lower in cluster 2.

Conclusions: Our results classified patients with oligoarticular, RF-negative polyarticular, and undifferentiated arthritis into 2 clusters. Wrist and elbow involvements and the number of involved arthritis were the most important factors in differentiating the 2 groups.