A 5-year-old child is brought to the emergency department by his parents for right arm pain. The patient reports that he was playing hide and seek outside and felt a sharp pain on his arm while hiding in some thick bushes. His parents suspect that something had stung him. Physical examination shows an edematous and erythematous plaque with mild central pallor. A residual stinger, located central to the lesion, is readily extracted. The physical examination is otherwise not significant. Which of the following substances is most likely directly responsible for the skin findings observed in this patient?

Question

A 5-year-old child is brought to the emergency department by his parents for right arm pain.  The patient reports that he was playing hide and seek outside and felt a sharp pain on his arm while hiding in some thick bushes.  His parents suspect that something had stung him.  Physical examination shows an edematous and erythematous plaque with mild central pallor.  A residual stinger, located central to the lesion, is readily extracted.  The physical examination is otherwise not significant.  Which of the following substances is most likely directly responsible for the skin findings observed in this patient?

Quizplus · Accepted Answer

Eductional Objective: Wheal-and-flare lesions usually result from allergic (type I hypersensitivity) reactions.  On initial exposure, an allergen (eg, insect venom) promotes antibody class switching to IgE.  Subsequent exposure promotes cross-linking of IgE on basophils and mast cells, resulting in degranulation and release of multiple vasoactive mediators, including histamine.

A 5-Year-Old Child Is Brought to the Emergency Department by His