Polyarthritis, Fever and a Rash in a Young Girl

A previously healthy six-year-old girl had developed a fever five days before presentation. Two days later, she had an onset of diffuse abdominal pain, intermittent vomiting and loose, nonbloody stools. On the fourth day of fever, she described pain on moving her arms and legs, and the following day, she was brought to the IWK Health Centre in Halifax, Nova Scotia. Her history showed up-to-date immunizations, and the absence of medications or known allergies. There was no history of trauma, infectious contacts, travel outside the Maritime provinces, or consumption of unpasteurized dairy products or undercooked meats. She had no history of animal exposure, except for a white rat kept in a cage in the family basement. On examination, she was febrile (38.8°C), unwell looking and tachycardic, but was oriented, normotensive and in no respiratory distress. Her head and neck examinations revealed periorbital edema, marked erythema of the buccal mucosa, and a ‘strawberry tongue’ with no oral ulcers, tonsillar exudate, cervical adenopathy or conjunctival injection. A blanching erythematous maculopapular rash was visible on the face, trunk, arms and legs, being most prominent on the hands and feet. A palpable, nonblanching petechial exanthem was also present on the palms of the hands and soles of the feet, with marked periungual erythema and capillary vessel dilation at the nail beds. No puncture marks or scratches were visible. The wrists, elbows, knees and small joints of the hands were swollen and warm to palpation, but without erythema. Any motion of these joints was limited and painful. There was periarticular swelling of the ankles and feet. The precordium was hyperdynamic, with a 2/6 vibratory systolic ejection murmur at the upper left sternal border. There were no bruits. There was no hepatosplenomegaly or generalized adenopathy. The white blood cell count was 6.0×109/L (56% neutrophils, 12% bands and 13% lymphocytes), the hemoglobin level was normal and the platelet count was 31×109/L. The C-reactive protein level and erythrocyte sedimentation rate were elevated at 219 mg/L (reference less than 5.3 mg/L) and 65 mm/h (reference 0 mm/h to 9 mm/h), respectively. Renal function and liver enzymes tests were normal. Urinalysis revealed trace blood, and hyaline and granular casts. Her chest radiograph and echocardiogram were normal. Empirical antibiotic therapy was started. A blood culture taken on the day of presentation was positive at 15 h. What is the diagnosis?

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