You see a 31/2-year-old child in the emergency department who has had fever for the past week. The parents relate that their son has some swollen glands, fever, and now seems to be getting a rash on his arms. On examination, you find an uncomfortable appearing young boy whose vital signs are normal with the exception of a temperature of 104. You note t hat he has a red posterior oropharynx with dry, cracked lips. His TMs are normal. He has mild conjunctival injection bilaterally without any discharge. His chest is clear, and his heart sounds are normal. He does not have any hepatosplenomegaly. His has a lacy, confluent macular rash on his chest and upper arms, with mild peeling of the tips of his fingers.
What is the most worrisome complication of this disease?