Acute suppurative oligoarthritis and osteomyelitis: A differential diagnosis that overlaps with acute rheumatic fever

Background: Acuterheumaticfever(ARF)isanillnesscausedbygroupAstreptococcus(GAS)infection,and remains the leading cause of acquired heart disease in worldwide. Distinguishing between ARF and septic arthritis may be difficult. This report describes a case of suppurative arthritis overlapping with ARF. Case presentation: A 4-year-old, previously healthy boy presented with fever and left leg pain. The level of anti-streptolysin O (ASO) was elevated. His throat swab cultures grew GAS, but none were detected in his synovial fluid. Magnetic resonance imaging revealed suspected arthritis and osteomyelitis. The patient was treated for septic arthritis, but was subsequently diagnosed with ARF, after the development of carditis. Conclusion: The clinical and laboratory features of ARF and suppurative arthritis demonstrate substantial overlap. Patients with an elevated ASO should undergo a careful cardiac examination for carditis associated with ARF by an echocardiogram. © 2015, Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases.