Approach to a fever (over 2 months) Quiz: Ace Your Exams

A 3-year-old previously healthy boy presents to the pediatrician for evaluation of six days of fever. He was initially seen on day 3 of illness and diagnosed with a viral upper respiratory tract infection. The fever has persisted, and parents report decreased fluid intake and urine output. Initial testing was negative for COVID-19 infection. Immunizations are up to date. He is at the 75^th percentile for height and 82^nd percentile for weight. Temperature is 38.4°C (101.1°F), pulse is 125/min, respirations are 28/min, blood pressure is 95/58 mmHg, and oxygen saturation is 99%. On physical examination, there is bilateral conjunctival erythema without discharge. There is no rhinorrhea. Tympanic membranes appear normal bilaterally. There is mild pharyngeal erythema. Diffuse, mobile, non-tender, and non-erythematous cervical lymphadenopathy is palpated with one lymph node measuring 2 cm. Cardiopulmonary examination reveals mild tachycardia without murmurs, rubs, or gallops. Lungs are clear to auscultation without increased work of breathing. On skin examination, there a widespread macular skin lesions on the trunk and extremities and erythema on the palms and soles. Which of the following additional findings would be consistent with the most likely diagnosis?