Pediatric allergies: Clinical

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Pediatric allergies: Clinical

USMLE® Step 2 questions

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USMLE® Step 2 style questions USMLE

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A 5-year-old boy comes to the emergency department with his mother because of a skin rash on his face that is very itchy for 20 minutes.  His mother says that within minutes of eating peanut butter, he vomited and developed hives on his face. Physical examination shows hives that appear red, raised, and are localized to his face. His medical history is noncontributory and he is up-to-date on his immunizations. His pulse is 90/min, respirations are 22/min, and blood pressure is 120/85 mm Hg. He does not have stridor on auscultation. Which of the following is the most likely explanation for this patient’s physical findings?


Allergies are an IgE-mediated Type I hypersensitivity reaction against a specific allergen. These include environmental triggers, like viral infections, animal dander, latex, pollen, and insect stings; foods, like nuts, shellfish, and eggs; and medications, like penicillins and sulfonamides. And these usually present first during childhood.

Now, allergic reactions happen in two steps.

Step one - exposure to the allergen causes allergen-specific IgE antibodies to bind to the surface of mast cells and basophils.

Step two - a repeat exposure to the allergen causes those mast cells and basophils to release proinflammatory molecules like histamine.

Generally, there are acute allergic reactions which resolve within 6 weeks, and chronic allergies which persist for more than 6 weeks.

Among the acute allergic reactions, the most common trigger is a viral upper respiratory tract infection.

One outcome is urticaria, also called hives, which are slightly raised, well-defined wheals that are 1 mm to 10 cm in diameter. They’re usually red, blanch with pressure, are extremely itchy, and can pop up anywhere in the body.

The key feature is that these lesions come and go very rapidly - meaning one might appear on the leg as another disappears from the arm. The reaction involves the epidermis and dermis layers of the skin, and the whole thing typically resolves within 24 hours.

Typically no treatment is needed, but if the itching is really bad, topical cooling moisturizers or oral second-generation histamine H1 blockers can be used like loratadine, desloratadine, fexofenadine, cetirizine, or levocetirizine. If these don’t work, immunomodulatory agents, like cyclosporine or methotrexate can also be used.


Allergies refer to an IgE-mediated Type I hypersensitivity reaction against a specific allergen. Allergies are due to an overreaction of the immune system to a substance that is typically harmless to most people. Triggers can include animal dander, latex, pollen, and insect stings, or drugs like penicillins and sulfonamides.

Common pediatric allergies include allergic rhinitis , asthma, eczema, and food allergies. Symptoms of allergies can vary depending on the type of allergy and the child's age. For example, a child with food allergies may experience stomach pain, vomiting, or difficulty breathing, whereas a child with eczema may have itchy, red, and scaly skin. Treatment options for allergies include avoiding the allergen, medications, and allergen immunotherapy (allergy shots).


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