A Complicated Limp: When Occam's Razor Fails

This is a case of an 8-year-old girl who presents to the emergency department unable to walk due to right hip and left ankle pain for 3 days. Her examination is notable for polyarthralgia with significant tenderness of the left ankle and a heart murmur. Arthrocentesis of the ankle was performed, and initial results were inconclusive. Magnetic resonance imaging of the left ankle demonstrated findings consistent with an infection of the joint space. Subsequent laboratory results were also diagnostic for acute rheumatic fever. This patient was treated for both septic arthritis and acute rheumatic fever. This case report reviews the differential diagnosis for arthritis as well as the diagnostic criteria for acute rheumatic fever. The case highlights the need to search for a second diagnosis if a unifying diagnosis fails to explain all of a patient's signs and symptoms.