Allergy

Question 1

Types of hypersensitivity reactions

Answer 1

Type I = immediate (<30 mins to 2 hours)
Type II = antibody mediated/cytotoxic (variable, minutes to hours)
Type III = immune complex (1-3 weeks)
Type IV = delayed type (2-7 days)

Question 2

Type I hypersensitivity

Answer 2

IgE mediated
Mediators: histamine, tryptase, leukotrienes, prostaglandins
E.g. anaphylaxis, urticaria, allergic asthma/rhinitis

Question 3

Type II hypersensitivity

Answer 3

IgM, IgG, IgA mediated
Target RBCs, platelets
Mediators: complement
E.g. haemolytic anaemia, thrombocytopenia, Goodpasture, ?ABO incompatibility

Question 4

Type III hypersensitivity

Answer 4

Antigen-antibody complexes
Mediators: complement, anaphylatoxin
E.g. serum sickness, hypersensitivity pneumonitis

Question 5

Type IV hypersensitivity

Answer 5

Effector molecules = lymphocytes
Mediators: cytokines (IFNy, TNFa, G-CSF)
E.g. Tb skin test reactions, contact dermatitis, GvHD

Question 6

Role of tryptase in anaphylaxis

Answer 6

Mast cell enzyme
Related to severity of anaphylaxis (but more likely to be elevated if pt was hypotensive)

Question 7

Symptoms of eosinophilic oesophagitis

Answer 7

Reflux symptoms, vomiting, dysphagia, abdominal pain, food impaction, FTT, slow eater/food refusal

Question 8

Most common triggers of eosinophilic oesophagitis

Answer 8

Dairy, wheat, egg, soy

Question 9

Diagnosis of eosinophilic oesophagitis

Answer 9

Mixed IgE and non-IgE allergy
Positive SPT, elimination diet
Biopsy showing >15 eosinophils

Question 10

Treatment and prognosis of eosinophilic oesophagitis

Answer 10

Elimination diet
Swallowed inhaled corticosteroids
Cx: fibrosis, strictures

Question 11

Symptoms of eosinophilic gastroenteritis

Answer 11

Abdominal pain, vomiting, irritability, poor appetite, FTT, weight loss, anaemia, protein losing enteropathy

Question 12

Investigations and management of eosinophilic gastroenteritis

Answer 12

Positive SPT +/- food IgE in 50%
Don’t need to treat as aggressively as eosinophilic oesophagitis (diet Mx)
Variable prognosis

Question 13

Features of allergic proctocolitis

Answer 13

Young infants <6 months
Cow’s milk, soy, breastfed
Blood streaked stools in healthy appearing/thriving infants
Mx: allergen elimination, majority can tolerate by 1-2 years

Question 14

Features of FPIES

Answer 14

Infants around solid food introduction
Rice, soy, cow’s milk
Profuse vomiting 2-3 hours post ingestion, acutely unwell +/- CVS collapse
Mx: elimination, rehydration, usually grow out of sensitivities

Question 15

Features of dietary protein induced enteropathy

Answer 15

Young infants
Protracted diarrhoea (mucous and blood), FTT, vomiting, abdominal distension
Usually cow’s milk trigger
Anaemic in 40%
Responds to dietary restriction, most self resolve

Question 16

Overview of penicillin allergy and cross reactivity

Answer 16

Cross reactivity is due to chemical similarity of beta lactate ring side chains - R1
Risk of allergy to cephalosporin in penicillin allergy is <2%
1st gen cephalosporins more likely to cross react than 2nd and 3rd gen

Question 17

Triggers of serum sickness

Answer 17

Blood products
Foreign proteins/antivenoms
Cefaclor, penicillin
Sulfonamides
Minocycline
Thiazides
Phenytoin

Question 18

Risk of anaphylaxis following sting reaction

Answer 18

More likely to have large localised skin reactions to a sting, <10% chance of anaphylaxis in future