Visual Diagnosis: A Rash That Changes Shape

Presentation

A previously healthy 9-month-old girl was admitted to the Children’s Hospital at Saint Francis/The University of Oklahoma because of fever and rash. The fever started 2 days before the admission, and her temperature was up to 102.0°F (38.9°C). The rash occurred on the day of admission. It began as red raised lesions on the trunk and progressed to circular and annular lesions of various sizes. New eruptions occurred while previous lesions were changing in shape within a few hours. The rash was progressing, also involving the extremities, despite the use of over-the-counter diphenhydramine.

The infant had been diagnosed as having acute otitis media and was on the ninth day of amoxicillin administration. She was fully vaccinated. The rest of her medical history was noncontributory. She lived with her foster father.

On physical examination her vital signs were within normal limits. She was in no acute distress, drinking milk from her bottle, and occasionally smiling. Polycyclic, annular erythematous, raised lesions were detected over the infant’s torso and upper and lower extremities (Figure). The rash did not involve the palms and soles. In …