An 18-year-old woman reported to the emergency department after 2 weeks of having fatigue, poor appetite, and general malaise. She reported no fevers, rhinorrhea, vomiting, diarrhea, or rash. She had 2 days of diffuse joint pains in her upper and lower extremities, particularly in her ankles and wrists. While in the emergency department, she developed severe, acute right wrist pain with swelling, erythema, and warmth. A fluid-filled lesion developed on the dorsum of her right hand (Figure 1 and Figure 2). She was febrile (39.4°C) and tachycardic, with normal respiratory rate and blood pressure. Serum white blood cell count was 8400/mL; hemoglobin level was 9.0 g/dL (to convert to grams per liter, multiply by 10.0; reference range, 12.0-16.0 g/dL); and C-reactive protein level was 6.1 mg/L (to convert to nanomoles per liter, multiply by 9.524). Arthrocentesis of her right wrist revealed purulent fluid (white blood cell count, 95 000/mL).