Differential diagnosisDownloads

An 8-year-old girl is brought to the emergency department because of a 2-day history of low-grade fever, itchy rash, and generalized joint pain. The rash initially started in the antecubital and popliteal fossae and then spread to her trunk and distal extremities. One week ago, she was diagnosed with acute sinusitis and was started on amoxicillin. She has no history of adverse drug reactions and immunizations are up-to-date. Her temperature is 37.5°C (99.5°F), pulse is 90/min, and blood pressure is 110/70 mm Hg. Physical examination shows periorbital edema and multiple erythematous, annular plaques of variable sizes over her entire body. One of the lesions in the right popliteal fossa has an area of central clearing and the patient's mother reports that it has been present for over 24 hours. Urinalysis is normal. Which of the following is the most likely diagnosis?

A 9-year-old boy is brought to the emergency department because of progressively worsening shortness of breath for 3 days. He has had fever and malaise for the past 5 days. He had a sore throat 3 weeks ago that resolved without treatment. He appears ill. His temperature is 38.6°C (101.5°F), pulse is 98/min and blood pressure is 84/62 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 93%. Examination shows jugular venous distension and bilateral ankle edema. There are erythematous, ring-shaped macules and patches over his trunk that are well-demarcated. Auscultation of the chest shows crackles at the lung bases bilaterally. An S3 is heard on cardiac auscultation. His hemoglobin concentration is 12.2 g/dL, leukocyte count is 13,600/mm3, and platelet count is 280,000/mm3. A urinalysis is normal. An x-ray of the chest shows cardiac silhouette enlargement with prominent vascular markings in both the lung fields. Which of the following is the most likely etiology of this patient's symptoms?