You are an experienced medical professor guiding me, a medical student preparing to study Anki flashcards focused on clinical reasoning and practical applications of medicine. Before I attempt the flashcards, please provide a comprehensive study session on the key topics. For each topic, offer clear and concise explanations, relevant clinical examples, and insights into how it applies to clinical decision-making. Then, challenge me with related questions to stimulate critical thinking (and provide the answers afterward). Be instructional yet accessible, balancing depth with conciseness.
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Allergic rhinitis is a subtype of rhinitis due to a type I hypersensitivity reaction (e.g. to pollen)	
Asthma is often associated with allergic rhinitis, eczema, and a family history of atopy	
Once produced, IgE binds to high affinity (FcεRI)::specific receptors on mast cells in the airway mucosa	Triggers mast cell degranulation on re-exposure to the antigen
ACE inhibitors are contraindicated in patients with hereditary angioedema, which is characterized by a(n) C1 esterase inhibitor (C1-INH) deficiency	ACE plays a role in bradykinin breakdown, so ACE inhibitors can lead to increased bradykinin activity
ACE inhibitors and neprilysin inhibitors may cause angioedema due to increased bradykinin	- Thus, contraindicated in patients with hereditary angioedema    - Kallikrein converts high molecular weight kininogen (HMWK) to bradykinin → edema (↑ vasodilation, ↑ permeability) and pain - Sacubitril is a neprilysin inhibitor, found in association with valsartan → guideline therapy for heart failure (neprilysin metabolizes ANP and BNP)     Photo credit: James Heilman, MD, CC BY-SA 3.0, via Wikimedia Commons
ARBs are used to treat hypertension, proteinuria, HF, or diabetic nephropathy in patients intolerant to ACE inhibitors	e.g., cough, angioedema
Allergic conjunctivitis is characterized by bilateral itchy eyes	IgE-mediated response to allergens; treatment involves avoidance of the triggering agent and topical agents (e.g. antihistamines, mast cell stabilizers)   Photo credit: James Heilman, MD, CC BY-SA 4.0, via Wikimedia Commons
IgE cross-links when exposed to allergen, mediating type I hypersensitivity reactions	- When multiple bound IgE on mast cells / basophils cross links a multivalent antigen, this pulls the FcεRI (high affinity IgE receptor) together   - Clumping of many FcεRI induces signalling that leads to degranulation
Type I HSR occurs due to cross-linking of IgE on presensitized mast cells and basophils by antigens, leading to receptor aggregation	- e.g., anaphylaxis   - This aggregates the FcεRI (high affinity) receptors on the mast cell, leading to the activation of non-receptor tyrosine kinases and down stream effects (degranulation)
The immediate response of mast cell and basophil activation is release of preformed histamine granules and tryptase::marker of activation	- Causes vasodilation of arterioles and increased vascular permeability  - Other preformed granules include heparin and eosinophil chemotactic factor
Which type of hypersensitivity mediates anaphylaxis (e.g., food, drug, or bee sting allergies)?  Type I HSR	If severe enough, can lead to death with laryngeal edema and lung hyperinflation (due to air being trapped from airway obstruction)
Mast cells may be activated by cross-linking of cell-surface IgE by antigen	- When multiple bound IgE on mast cells / basophils cross links a multivalent antigen, this pulls the FcεRI (high affinity IgE receptor) together  - Clumping of many FcεRI induces signalling that leads to degranulation
C1 esterase inhibitor deficiency results in hereditary angioedema	- C1 inhibitor (AKA C1-esterase inhibitor) normally inhibits kallikrein, which is responsible for conversion of HMWK to bradykinin  - Deficiency leads to high levels of serum bradykinin → episodes of swelling and edema  - Can treat with icatibant (bradykinin B2 receptor antagonist), C1-inhibitor concentrate, or ecallantide (kallikrein inhibitor)  Photo credit: James Heilman, MD, CC BY-SA 3.0, via Wikimedia Commons
What is the best treatment to minimize the development of life-threatening complications in patients with anaphylaxis (e.g., hypotension, upper airway edema)?   Intramuscular epinephrine 1:1000 (1 mg/mL)::include ROA	- IV epinephrine is indicated for patients with anaphylaxis who do not respond to initial IM epinephrine (IV is associated with a higher risk of cardiovascular arrhythmia)   - α1 stimulation for vasoconstriction (increases blood pressure and reduces edema) - β2 stimulation for bronchiole dilation - Some cases require additional doses of epinephrine for refractory symptoms - Can also use H1/H2 blockers, albuterol, steroids
What is the likely diagnosis in a patient with well-circumscribed and raised erythematous plaques with intense pruritus (pictured below)? The rash occurs episodically >6 weeks, approximately 2 - 3x/day, with each episode lasting about 6 - 8 hours   Chronic spontaneous urticaria	Photo credit: James Heilman, MD, CC BY-SA 3.0, via Wikimedia Commons   - Due to mast cell activation   - Work-up includes biopsy to rule out urticarial vasculitis or mastocytosis
"What is the likely diagnosis in a patient with a history of asthma that presents with sudden onset redness, watery discharge, and itching of both eyes? The conjunctiva has a ""bumpy"" or granular appearance with diffuse injection   Allergic conjunctivitis"	Photo credit: James Heilman, MD, CC BY-SA 4.0, via Wikimedia Commons  Allergy = affects both eyes
What is the recommended initial treatment for patients with allergic rhinitis?   Intranasal glucocorticoids	Oral antihistamines, antihistamine or cromolyn nasal sprays, and leukotriene modifiers can be considered as well   Photo Credit: https://www.myupchar.com/en, CC BY-SA 4.0, via Wikimedia Commons
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