Long-term outcome studies of JIA show huge variation, with between 2% and 48% of JIA patients developing severe functional limitation (Stein-brocker classes III and IV or HAQ score > 1.5) (33). The length of follow-up strongly influences long-term outcome. In adult RA, Scott (34) prospectively followed up aggressively DMARD treated patients at 5, 10, and 20 years. Although function initially improved, it deteriorated considerably between 10 and 20 years. These findings are mirrored in JIA; in 1966
Laaksonen (27) demonstrated that the natural history of JIA is for poor physical function to increase from 12% at 3 to 7 years after onset, to 48% after 16 or more years.
However, over the past 40 years the impact of JIA upon long-term physical function appears to have reduced, probably related to improving treatments. Figure 1 shows the improvement in function seen when publications on long-term outcome in JIA (35) are grouped together into each decade in which disease onset occurred.
Disease subtype has a strong impact upon long-term functional outcome. Systemic onset JIA and rheumatoid factor negative polyarthritis JIA are related to poor functional outcome and persistent oligoarticular and enthesis-related JIA are associated with relatively few functional problems (Table 7) (3).
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