Objective: To investigate the relationships between systemic onset juvenile idiopathic arthritis disease activity, course of the disease, and functional class according to Steinbrocker.
Methods: The records of all children with systemic onset juvenile arthritis (JA) according to the American College of Rheumatology criteria attending our center since 1971 with a minimum followup period of 3 years were reviewed. A cohort of 80 consecutive patients entered the study: 42 males, 38 females, mean age at onset 6.3 years (range 0.7-16), mean followup period 10.7 years (range 3-33). The cumulative duration of the active periods (CDAP) in months was calculated for every patient.
Results: Three patterns of disease course were apparent: monocyclic (subtype I), intermittent (subtype II), and persistent (subtype III). At the last control the functional class and disease activity status were evaluated. In all subtype I patients (9 cases) the disease was in remission and no patient was in class II, III, or IV. In subtype II patients (27 cases), 16 were inactive or in remission and 6 in class III. In subtype III (44 cases) 21 were inactive or in remission and 17 were in class III or IV. The equation relating the Steinbrocker class to the CDAP was calculated considering the functional outcome as the dependent variable. The linear regression equation y = 0.0083 x + 1.266 was found with a correlation coefficient r = 0.586 (p < 0.0001). The majority of our patients were treated with disease modifying antirheumatic drugs, which in many cases were effective in reducing the duration of the active phases of disease.
Conclusion: Systemic onset JA may present with different clinical courses; the functional outcome is always good in subtype I (monocyclic), but can be poor in subtypes II and III. The severity of disability evaluated according to Steinbrocker classes is dependent on the cumulative duration of the active periods of the disease.