Allergy

Question 1

Define Intolerance

Give example

Answer 1

Intolerance is where a substance elicits an adverse reaction w/o the immune system being involved.

Often b/c of enzyme deficiences, e.g. lactose intolerance

Question 2

Anaphylaxis

• Define
• Symptoms

Answer 2

Type 1 hypersensitivity reaction mediated by IgE antibodies against allergen, present on mast cells and basophils. 
Signs and symptoms: 
Vascular shock, low BP and syncope 
Bronchospasm --> wheeze 
Uritcaria 
Angioedema 
Laryngeal oedema --> stridor and airway obstruction 
Abdo pain, vomitting, diarrhoea

Question 3

Examples of triggers of anaphylaxis

Answer 3

Arthropod venoms (e.g. bee, wasp stings)
Drugs:
1) IV and oral antibiotics- beta-lactams
2) Neuromuscular agents- suxamethonium
3) Peptide hormones- ACTH, insulin
4) Plasma
5) Foods- peanuts, true nuts

Question 4

Treatment for Anaphylaxis

Answer 4

1) Adrenaline IM 1:1000 (500 micrograms in adult, so 0.5mL)
2) Establish airway
3) High flow O2
4) IV Fluid Challenge (500ml-1000ml)
5) Chlorphenamine 10mg IM
6) Hydrocortisone 200mg IM

Question 5

Anaphylactoid Reactions

• define
• triggers

Answer 5

Inv. a direct or indirect activation of mast cells w/o IgE
Can be caused by drugs, e.g. opiates, vancomycin, NSAIDs
Physical stimulant: exercise, cold and trauma

Question 6

Scromboid

Answer 6

Massive ingestion of histamine, from decayed mackerel or other oily fish
Mast cells are not inv. therefore tryptase -ve

Question 7

Urticaria

• define
• causes

Answer 7

A raised, itchy, erythematous rash: wheals/hives
Classified as acute or chronic (>1month)
Can be allergic- same as anaphylaxis, anaphylactoid, scromboid
Infections: H. pylori, Hep. B, lyme disease
Autoimmune: autoantibodies to FcE receptors on basophils, mast cells
Vasculitis- more painful

Question 8

Cold Urticaria

Answer 8

Cryoglobulinaemia (SLE, leukemias, lymphomas, idiopathic)

Inherited: C1AS1 gene mutation

Question 9

Autonomic Urticaria

Answer 9

Cholinergic urticaria- assoc. w/ heat and sweating

Adrenergic urticaria b/c of stress

Question 10

Exercise Urticaria

Answer 10

?assoc. w/ IgE to omega-gliadin

Hx. of exercise within hours of meal containing gluten

Question 11

Treatment for Urticaria

Answer 11

Anti-histamines- cetrizine, fexogenidine, loratidinele
H2 Antagonist- Ranitidine
Montelukast- leukotriene inhibitor
If all this fails in chronic urticaria, use omalizumab

Question 12

Angioedema

-define

Answer 12

Swelling of subcutaneous tissues due to fluid collection caused by release of inflammatory mediators, esp. histamine.

Question 13

Causes of Angioedema

Answer 13

Histamine (+/- leukotriene) mediated: allergic, idiopathic
Bradykinin (+/- complement) mediated: hereditary angioedema, acq. C1 esterase inhibitor deficiency, idiopathic (normal C1 esterase)

Question 14

Hereditary Angioedema

-3 types

Answer 14

TYPE 1- deficiency of C1 esterase inhibitor (which restrains classical complement and bradykinin pathways)
TYPE 2- mutation of C1 esterase inhibitor
TYPE 3- mutation of Factor XII gene (initiated bradykinin and intrinsic clotting pathways)

Question 15

Presentation of Hereditary Angioedema

Answer 15

Episodes of angioedema of limbs, trunk, perineum, face and within mouth and airway
Can be intra-abdo –> pain and swelling
C4 Low

Question 16

Acquired C1 Esterase Inhibitor Deficiency

Answer 16

Caused by autoimmune disease, haematological malignancy, infections (Hep. B/C, H. pylori), drugs (ACE-I)
C4 Low, C1q N/L and anti-C1q antibodies may be present

Question 17

Treatment of Angioedema

Answer 17

If allergic, same as anaphylaxis
C1 esterase deficiency: anabolic steroids which increase C1 esterase production
C1 inhibitor IV
Icatbant and Lanadelumab inhibit the bradykinin pathway (emergency treatment)
If idiopathic: tranxemic acid