Hypersensitivity disorders

Question 1

What occurs in type 1 hypersensitivity disorders? Give 3 pathophysiological changes in the body as a result of a reaction.

What is the atopic triad?

Answer 1

Immediate reaction provoked by re-exposure to an allergen. IgE mediated: mast cells release mediators resulting in vasodilation, increased permeability, smooth muscle spasm.

Atopic triad is eczema, asthma and hay fever.

Question 2

Give some typical symptoms of a type 1 hypersensitivity reaction.

Answer 2

• Angioedema
• Urticaria
• Rhinoconjunctivitis
• Wheeze
• D&V
• Anaphylaxis

Question 3

Give some disease examples of type 1 hypersensitivity.

Answer 3

Most use skin prick test

• Food allergy
• Atopic dermatitis
• Oral allergy syndrome
• Latex food allergy- food with latex-like components: avocado, banana, potato, tomato, kiwi etc.
• Allergic Rhinitis
• Acute Urticaria- 50% caused by food, drugs, latex, viral infections. 50% idiopathic.

Question 4

What is anaphylaxis? What are the two immune mechanisms and their triggers?

Answer 4

A severe systemic allergic reaction causing respiratory difficulty and hypotension.

IgE mediated mast cell degranulation- peanut, penicillin, stings, latex.
Non- IgE mediated mast cell degranulation- NSAIDs, IV contrast, opioids, exercise

Question 5

Give differential diagnoses for anaphylaxis

Answer 5

• C1 inhibitor deficiency- hereditary angioedema
• ACEi induced angioedema
• Acute anxiety
• Urticaria

Question 6

What is the management for anaphylaxis?

Answer 6

Elevate legs, 100% oxygen, IM adrenaline 500mcg, inhaled bronchodilators, hydrocortisone 200mg IV, chlorphenamine (antihistamine) 10mg IV, IV fluids, Seek help.