Allergies

Question 1

Define hypersensitivity

Answer 1

objectively reproducible symptoms or signs following exposure to a defined stimulus (e.g. food, drug, pollen) at a dose that is usually tolerated by most people

Question 2

Define allergy

Answer 2

a hypersensitivity reaction initiated by specific immunological mechanisms. This can be IgE-mediated (e.g. peanut allergy) or non-IgE- mediated (e.g. coeliac disease)

Question 3

Define atopy

Answer 3

a personal and/or familial tendency to produce IgE antibodies in response to ordinary exposures to potential allergens, usually proteins. Strongly associated with asthma, allergic rhinitis and conjunctivitis, eczema and food allergy

Question 4

Define anaphylaxis

Answer 4

a serious allergic reaction with bronchial, laryngeal, or cardiovascular involvement that is rapid in onset and may cause death

Question 5

Define immune tolerance

Answer 5

the absence of an active immune response against a particular antigen, e.g. the absence of an allergic immune response to peanut or house dust mite

Question 6

Define sensitisation

Answer 6

a positive test to an allergen, either by skin prick test, or specific IgE. Does not equate to allergy unless a clinical reaction is initiated on exposure. However, the higher the number of positive tests, the more likely the person is going to be “allergic”

Question 7

Describe IgE-mediated allergies

Answer 7

Follows exposure and sensitisation to trigger food allergen(s) with the development of serum-specific IgE antibody
Accounts for the majority of life threatening allergic reactions
Produces immediate and consistently reproducible symptoms which may affect multiple organs including GIT, respiratory, CV and neurological systems

Question 8

What are the two phases of IgE mediated allergies

Answer 8

Early phase: histamine and mast cell mediator release within minutes of exposure
→ Causes urticaria, angioedema, sneezing, vomiting, bronchospasm, and/or cardiogenic shock

Late phase: may occur 4-6 hours (especially for inhalant allergens)
→ Causes nasal congestion, cough, bronchospasm

Question 9

What is oral allergy syndrome

Answer 9

localising food allergy which may occur due to cross-reactivity between aeroallergens (results in IgE response to epitopes in fruits and vegetables on oral contact)

Question 10

Describe non-IgE mediated allergy

Answer 10

Cell-mediated (T cell) mechanisms
Tends to occur in young children

Question 11

Give examples of common allergens

Answer 11

Inhalant allergens, e.g. house-dust mite, plant pollens, pet dander and moulds
Insect stings/bites, drugs, and natural rubber latex.
Ingestant allergens, e.g. egg, cow’s milk, nuts, wheat, seeds, legumes, seafood and fruits

Question 12

What are the common food allergens in younger vs older children

Answer 12

Infants- most common causes are milk, eggs and peanut
Older children- peanut, tree nut, fish, shellfish

Question 13

What are the risk factors for allergy

Answer 13

PMHx atopy or anapylaxis
FMHx of atopy (asthma, eczema, rhinitis)
Occupation, recreational, geographical exposure to allergens
Hygiene hypotheses (lower risk of allergy in children of large families and those raised in farms, modern living conditions = increased allergy)

Question 14

What is the allergic march

Answer 14

The progression of allergic diseases from an initial diagnosis e.g. eczema in infancy to asthma later on in life,
INFANCY
* Eczema
* Food allergy

PRESCHOOL/ PRIMARY SCHOOL
* Allergic rhinitis
* Conjunctivitis
* Asthma

Question 15

What proportion of children in the UK have an allergic disorder

Answer 15

40%

Question 16

What are the symptoms of IgE mediated allergy

Answer 16

Urticaria
Facial swelling
Anaphylaxis within 10-15 minutes
GIT: N&V, diarrhoea, colicky abdominal pain
ENT: nasal itching, sneezing, rhinorrhoea
Respiratory: cough, chest tightness, wheeze, mouth breathing
Sleep: Hx apnoea/snoring

Question 17

What are the symptoms of non-IgE mediated allergy

Answer 17

GIT: N&V, diarrhoea, colicky abdominal pain, blood in stools (Proctitis, severe vomiting)
Faltering growth

Question 18

What are the signs of allergy on examination

Answer 18

Obs
Height and weight + growth charts

General: urticaria, facial swelling, sneezing, rhinorrhoea, eczema

ENT: mouth breathing, allergic salute, pale and swollen inferior nasal turbinates

Resp: cough, wheeze, hyperinflated chest, harrison sulci

Eyes: conjunctivitis → Denni-morgan folds (prominent creases), blue-grey discolouration below the lower eyelids

Question 19

What investigations are done for allergy

Answer 19

Serum-specific IgE allergy testing (RAST): raised response

Skin prick testing (ensure antihistamines are stopped)
Double-blind placebo controlled food challenge (must be done in hospital)

Question 20

What is the management for allergies

Answer 20

Avoidance of relevant allergen
Individualised written allergy management plan
Education: allergy UK, british dietetic association
Review annually

Mild reactions: PO non-sedating antihistamines PRN

Proteins with an unstable tertiary structure may be rendered non-allergenic by heat degradation or other forms of processing e.g. milk, eggs

Question 21

What factors necessitate referral to the allergy specialist

Answer 21

Faltering growth with ≥1 GI symptoms of allergy
Severe atopic eczema
Multiple allergies
≥1 acute systemic or severe delayed reactions
Persisting suspicion

Question 22

What is an allergen challenge

Answer 22

Food allergies may resolve in childhood, where gradual re-introduction may be tried
The child is given increasing quantities of the food, starting with a tiny amount, until a full portion is reached.
Sometimes these are ‘placebo controlled’, where the child and parents do not know which of the challenges involves the food or a placebo
The test should be performed in a hospital with full resuscitation facilities available, with close monitoring for signs of anaphylaxis

Question 23

What are the complications of allergy

Answer 23

Anaphylaxis, death
Stress and anxiety
Reduced QoL
Restricted diet and malnutrition

Question 24

What is the prognosis for allergies

Answer 24

Most kids outgrow their food allergy - eggs and cow milk
Certain food allergies are most likely to persist - Nuts and seafood