Erythema Marginatum — Rheumatic Fever

A 9-year-old girl from rural Tamil Nadu presents with a 3-week history of migratory polyarthritis affecting her knees and ankles, along with a non-pruritic pink rash with serpiginous borders and central clearing on her trunk. Her mother reports a sore throat 2 weeks prior. On examination, she has a new systolic murmur at the apex. The structure marked **D** in the diagram represents a major criterion for rheumatic fever. Which of the following is the most important clinical implication of this diagnosis?