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Outcome Measures for Juvenile Idiopathic Arthritis Disease Activity

Juvenile idiopathic arthritis (JIA) is a chronic inflammatory disease with a widely variable clinical course and outcome (1). Persistently active disease and prolonged synovial inflammation may cause destructive damage to joint structures (2), and the morbidity of the disease and treatments can lead to serious impairments of physical function, which have a marked impact on the quality of life of children and their families (3,4). Therefore, the evaluation of disease activity is a fundamental component of the clinical assessment of children with JIA. Children and adolescents deserve specific instruments or items that take into account the effects of the disease on physical and mental age–related issues that are inherent in growth and development. Therefore, adultoriented outcome measures are not necessarily suitable for use in pediatric patients and need to always be subjected to a critical evidencebased evaluation of their measurement properties in children and adolescents. Quantitative clinical assessment of children with rheumatic disorders entails some distinctive issues. In most clinical settings, the appraisal of the impact of the disease on a child’s health is obtained from a caregiver by means of proxyreported questionnaires. However, previous analyses have shown that parents and children often differ in their perceptions of health. This discordance has led to suggestions that both parent proxyreporting and children selfreporting be incorporated in pediatric rheumatology clinical care (5). The following psychometric analysis is based on currently published literature, with abstract publications excluded. All JIA disease activity measurement tools discussed herein produce a single continuous index of disease activity. Tables 1 and 2 provide a summary of practical applications and psychometric properties of the selected measures. These tools create better consistency in disease activity evaluation across physicians, allow patients to better understand the meaning of “disease activity” by providing a single number, increase the power of clinical trials, and reduce the samplesize requirements in clinical trials. In this review, we decided not to include two important outcome measures for JIA: the American College of Rheumatology (ACR) provisional definition of inactive disease (and clinical remission on/off medication) (6) and the definition of minimal disease activity (7). These are dichotomic definitions based on multiple criteria that do not allow for quantification of the level of disease activity of the patient. For the same reason, we did not include the ACR definition of improvement (8) as well. The definition of improvement is an important measure ideally suited to assess the magnitude of response to treatment, especially in clinical trials. However, it is dependent on the level of disease activity at baseline and does not permit the comparison of the level of disease activity between different patients. Only continuous measures of disease activity specifically designed for JIA were included in the present review: the physician (provider) and the parent/patient visual analog scales (VAS) and three composite disease activity scores. In the literature, nomenclature about the physician and the parent/patient VAS has been inconsistent; herein, the former has been abbreviated as MD global; the latter has been abbreviated as PGA.