Assessment of disease activity in juvenile idiopathic arthritis. The number and the size of joints matter.

Objective: Variables for assessment of disease activity of juvenile idiopathic arthritis (JIA) were studied, in order to develop a disease activity score for children with JIA.

Methods: One randomly chosen hospital visit was studied for each of 312 patients with JIA, with regard to disease activity variables. The physician global assessment score visual analog scale (physician GA) was used as a dependent variable in comparisons between potential disease activity variables. Previous studies have shown this variable to be the most sensitive to changes in JIA disease activity and to be comparable between patients.

Results: Based on Spearman's rank order correlation the number of active joints had a strong association with the physician GA. The median physician GA score rose markedly for each active large joint, but less for small joints, although small joints were also statistically important in assessing disease activity. Among the laboratory data, the erythrocyte sedimentation rate, C-reactive protein level, and platelet count showed weak correlations to the physician GA.

Conclusion: In preparation of a disease activity score for children with JIA the importance of both the number and size of joints involved needs further evaluation.