A 4.5-year-old boy with Diffuse Purpuric Lesions all Over his Extremities

A 4.5-year old boy is admitted to the pediatric Emergency Room with diffuse purpuric lesions all over his extremities. He is alert but has a fever (38.4 oC). He also has slight joint swelling in the left knee and both ankles. He had a fever and sore throat for the past two days. His primary care doctor gave him oral penicillin. From today morning, he developed the rash which progressed proximally from both feet to thighs and upper extremities including palms and soles. His past medical history is unrevealing. Family history is negative for any significant disease. The review of systems is unremarkable. The mother says she has not given any medication to him. On physical examination, he is a tachycardic boy with a blood pressure of 130/90 mmHg and a respiratory rate of 22/min. Eyes are normal, the soft palate has several petechiae and the face shows mild edema. Both hands are mildly edematous. There are diffuse non tender, nonblanching purpuric lesions on the arms, legs, and buttocks (Fig 1). The lungs and heart examination are normal. The abdomen is diffusely painful on palpation without rebound tenderness or guarding and without liver and spleen enlargement.