Discoid meniscus presenting as juvenile rheumatoid arthritis.

Discoid meniscus is a mechanical lesion described as having little inflammatory reaction. We describe a child with lateral discoid meniscus misdiagnosed as juvenile rheumatoid arthritis (JRA). Synovitis responded to aspirin, but function gradually deteriorated with increasing flexion deformity until arthrotomy and meniscectomy. Histology showed intense inflammatory changes compatible with JRA. Clinical and laboratory clues to early diagnosis were the localized nature of the inflammation on physical examination, radiographs and bone scan.