Allergies Flashcards
Define hypersensitivity
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
Define allergy
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)
Define atopy
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
Define anaphylaxis
a serious allergic reaction with bronchial, laryngeal, or cardiovascular involvement that is rapid in onset and may cause death
Define immune tolerance
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
Define sensitisation
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”
Describe IgE-mediated allergies
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
What are the two phases of IgE mediated allergies
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
What is oral allergy syndrome
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)
Describe non-IgE mediated allergy
Cell-mediated (T cell) mechanisms
Tends to occur in young children
Give examples of common allergens
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
What are the common food allergens in younger vs older children
Infants- most common causes are milk, eggs and peanut
Older children- peanut, tree nut, fish, shellfish
What are the risk factors for allergy
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)
What is the allergic march
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
What proportion of children in the UK have an allergic disorder
40%
What are the symptoms of IgE mediated allergy
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
What are the symptoms of non-IgE mediated allergy
GIT: N&V, diarrhoea, colicky abdominal pain, blood in stools (Proctitis, severe vomiting)
Faltering growth
What are the signs of allergy on examination
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
What investigations are done for allergy
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)
What is the management for allergies
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
What factors necessitate referral to the allergy specialist
Faltering growth with ≥1 GI symptoms of allergy
Severe atopic eczema
Multiple allergies
≥1 acute systemic or severe delayed reactions
Persisting suspicion
What is an allergen challenge
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
What are the complications of allergy
Anaphylaxis, death
Stress and anxiety
Reduced QoL
Restricted diet and malnutrition
What is the prognosis for allergies
Most kids outgrow their food allergy - eggs and cow milk
Certain food allergies are most likely to persist - Nuts and seafood
