A child scratches his hand with pen.A red wheal appears which persists for 30 minutes. What would be the diagnosis?
**Core Concept**
The child's symptoms are consistent with an immediate hypersensitivity reaction, specifically a type I hypersensitivity reaction, which involves the release of histamine and other mediators from mast cells. This reaction is mediated by IgE antibodies.
**Why the Correct Answer is Right**
The appearance of a red wheal, also known as a wheal-and-flare reaction, is characteristic of an immediate hypersensitivity reaction. The wheal is caused by increased blood flow and permeability of the skin vessels, leading to edema and erythema. The reaction is short-lived, persisting for 30 minutes or less. The involvement of IgE antibodies and the release of histamine and other mediators from mast cells are key features of this reaction.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the symptoms or the underlying mechanism of the reaction.
* **Option B:** This option is incorrect because it refers to a delayed hypersensitivity reaction, which involves T cells and is mediated by cell-mediated immunity, not IgE antibodies.
* **Option C:** This option is incorrect because it refers to a urticarial vasculitis, a type of vasculitis that affects the blood vessels and is not typically associated with an immediate hypersensitivity reaction.
**Clinical Pearl / High-Yield Fact**
Remember that immediate hypersensitivity reactions are mediated by IgE antibodies and are characterized by the release of histamine and other mediators from mast cells, leading to symptoms such as wheal-and-flare reactions.
**Correct Answer:** D. Urticaria (Hives)