Rheumatic fever presenting as monoarticular arthritis.

Background: Monoarticular arthritis in children is most often suppurative septic arthritis (SA) of bacterial origin. We recently cared for 3 patients with monoarticular arthritis who developed carditis while receiving antibiotics for SA. Distinguishing SA from rheumatic fever (RF) is critical to avoid lifelong cardiac complications associated with RF.

Methods: We compared the 3 cases of RF presenting with monoarticular arthritis with 12 cases of culture-confirmed SA to assess the clinical and laboratory differences between the 2 groups.

Results: Erythrocyte sedimentation rate, C-reactive protein and mean synovial fluid white blood cell counts were elevated in both groups. Mean antistreptolysin O (ASO) and anti-DNase B titers were elevated in patients with RF.

Conclusions: The clinical and laboratory features of RF and SA demonstrate substantial overlap. Patients with monoarticular arthritis and sterile synovial fluid cultures should have RF included in their differential diagnoses. Patients with an elevated ASO and/or anti-DNase B titer should have a careful cardiac examination looking for clinical evidence of carditis. Echocardiogram should be considered if clinical carditis associated with RF is suspected.