Allergy and Immunology: Rhinitis, Testing, and Immunotherapy
Allergy questions focus on allergic rhinitis, testing, and immunotherapy. Understand the IgE-mediated pathway: allergen cross-links IgE on mast cells, causing histamine release and symptoms (sneezing, rhinorrhea, congestion, itchy eyes). Differentiate allergic rhinitis from nonallergic rhinitis (vasomotor, medication-induced, hormonal) and from infectious rhinitis.
Know the testing options: skin prick testing (fast, sensitive) and serum-specific IgE (useful when skin testing is not feasible). Interpret results in clinical context-positive tests without symptoms do not equal allergy. First-line therapy is intranasal corticosteroids plus antihistamines; add leukotriene receptor antagonists in selected patients. Allergen immunotherapy (subcutaneous or sublingual) modifies disease and is indicated for refractory symptoms or poor medication tolerance.
Recognize anaphylaxis as a medical emergency: epinephrine first, then airway support and adjuncts. Know that aspirin-exacerbated respiratory disease involves asthma, polyps, and aspirin sensitivity, and that chronic urticaria is often idiopathic.
Traps: treating nonallergic rhinitis with immunotherapy; missing anaphylaxis in a patient with mild symptoms but airway involvement; and forgetting that skin testing can be falsely negative with antihistamine use.
Rule of thumb: "Test to confirm, treat symptoms first, and reserve immunotherapy for refractory or medication-limiting disease."
Worked example: A patient with seasonal sneezing, positive skin prick tests to grass, and inadequate response to intranasal steroids and antihistamines is a candidate for allergen immunotherapy.