A 20-year-old woman from a remote northern community presents to the office with a 2-week...

This presentation is most consistent with acute rheumatic fever (ARF): a history of pharyngitis 4 weeks earlier, migratory large-joint pain/swelling (knee then elbow), subcutaneous nodules over extensor surfaces, and prolonged PR interval (a Jones minor criterion indicating cardiac involvement). MCCQE objectives emphasize that diagnosing ARF requires meeting Jones criteria plus evidence of preceding group A streptococcal (GAS) infection. Because the sore throat occurred weeks ago, a pharyngeal culture is often negative and is less useful for establishing prior GAS infection. The most appropriate test is therefore an antistreptolysin O (ASO) titre (or other streptococcal serology such as anti–DNase B), which documents a recent streptococcal immune response and supports the diagnosis. Echocardiography can assess severity of carditis/valvular disease, but it does not provide the required evidence of preceding GAS infection. Rheumatoid factor and biopsy of nodules do not address the likely ARF diagnosis.