Correlation between conventional disease activity measures in juvenile chronic arthritis

Objective - To estimate in a cross sectional analysis the degree of colinearity among the disease activity measures more commonly used in juvenile chronic arthritis (JCA). Methods - This study assessed in a single clinical evaluation three subjective variables, three measures of functional capacity, eight articular indices, and two laboratory indicators of systemic inflammation in 55 consecutive children with JCA. The relation between the clinical measures of JCA activity was determined by Pearson correlation coefficients. An r value of 0.7 or greater was considered evidence of colinearity. Results - Among the subjective variables, parent global assessment of overall well being and parent assessment of pain were correlated with each other; the physician assessment of disease activity did not show evidence of colinearity with any other variable. The functional status measures were correlated with each other, but not with the indices of articular inflammation. There was a high degree of colinearity among the articular variables, with the number of active joints and the overall severity score being correlated with each other as well as with all the single articular indices. The laboratory variables were correlated with each other, but not with any of the articular, functional or subjective variables. Conclusion - Our results show a high degree of colinearity among the disease activity measures belonging to the same category, whereas this is uncommon for variables that investigate different domains of disease activity. These data underline the need to include the evaluation of each domain in the assessment of JCA activity.