Objective. To conduct a cross-sectional, community-based, point prevalence study of inflammatory joint disease and other rheumatic disorders in 12-year-old children in a metropolitan community.

Methods. After completion of a pilot study of 816 10-year-old children, a cross-sectional prevalence study was performed 2 years later on a randomized sample of 2241 12-year-old children (including the cohort from the pilot study) from a community of approximately 221 700 children aged 12 years or younger, with 17 300 children aged approximately 12 years. A rheumatologic examination was performed on each child by a single observer after perusal of completed questionnaires from parents and children.

Results. Three of 816 children in the pilot study were shown to have juvenile chronic arthritis (JCA), fulfilling the criteria of the European League Against Rheumatism for the diagnosis of JCA. Only 1 of 3 had a previous diagnosis of JCA. The prevalence was 3.7 per 1000. Of 2241 children examined 2 years later, 89% returned two questionnaires (one completed by the parent and one by the child). At examination, 38 swollen joints were identified in 32 children. Nine children were identified with JCA, of whom 7 had not had previous diagnoses. No questions from the questionnaires identified the 7 children with previously undiagnosed JCA. The point prevalence of JCA in this community was 4.0 per 1000. Although the children with newly diagnosed cases tended to have mild disease, it was associated with significant morbidity and the potential for serious morbidity.

Conclusions. This is the first reported prevalence study of JCA in which case ascertainment was based on clinical examination by a rheumatologist of children within a community. The prevalence of 4.0 per 1000 was significantly higher than the accepted prevalence of 0.6 to 1.1 per 1000. A study based on known cases would have significantly underestimated the true prevalence of JCA in this community, with 7 of 9 cases being previously undiagnosed. Questionnaires were not effective in identifying children with undiagnosed JCA, clinical examination supported by a history from the parent and child providing the only reliable means of diagnosis. It is possible throughout the world that the numbers of undiagnosed cases of JCA significantly exceed the numbers of known cases, with the true prevalence being significantly higher than the levels currently accepted.

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