What is the definition of an allergy?
- Immunological hypersensitivity that can lead to a variety of different diseasess via different patho-mechanisms
- Not a disease itself but mechanism leading to a disease
Define the following:
Define the following:
- Food allergy
How can allergies present differently and what are some of their symptoms and triggers?
- Allergic rhinitis
- Allergic conjuctivitis
- Asthma (allergens not the most common trigger)
- Atopic dermatitis / eczema (allergen avoidance like dietary exclusion rarely improves symptoms)
- Insect allergy
- Food allergy
- Drug allergy
How can you tell the difference between allergic conjunctivitis compared with other causes like viral?
Allergic is itchy
What are the most common allergic conditions in the following groups:
- Pre school children
- School aged children
- Preschool: eczema and food allergy
- School: asthma
- School to adult: rhinitis and conjunctivitis
How does the prevalence of allergic diseases change over a lifetime?
- Asthma presents in school aged children then improves and decreases in prevalence with age as well as food allergies
- Pollen allergies are detected at young age but the prevalence increases with age
- Rhinitis and Conjunctivitis develop late in childhood and then increase in prevalence into adulthood
Why are allergies important?
- Allergy is common
- Allergy is associated with significant morbidity
- Allergy can be fatal
What is food intolerance?
Food intolerance are numerous adverse responses to foods that do not involve an immune response
What are the major food allergies?
- Over 170 IgE mediated reactions to food but most common is milk, eggs, and peanuts
- Self reported food allergies a lot higher than actual prevalence
How do we classify the different adverse reactions to food?
Take note of highlighted
What is the mechanism behind having an adverse reaction to spoiled oily fish?
When fish like mackerel and tuna spoil they produce histamine in the process of decay causing symptoms similar to allergy when eaten
What are the two main phenotypes of food allergy and what are the differences between the two?
- Immediate onset/IgE mediated: affects skin, GI tract, respiratory and CVS
- Delayed onset/Non-IgE mediated: affects GI tract and possibly causes eczema
What are some of the different presentations of IgE and Non-IgE mediated food allergy? (give examples for each system affected)
Identify three ways in which allergy is associated with significant morbidity.
- AR can impair sleep and reduce productivity
- Hospital admissions for asthma cause high absenteeism
- Restrictive diets in food allergy cause social exclusion and malnutrition
What are some different presentations of IgE mediated food allergies?
PFS: doesn't cause systemic symptoms as heat and stomach acid denatures pollen. Also only causes symptoms in unprocessed foods e.g apples
What are some different presentations of Non-IgE mediated food allergies?
- Mainly GI symptoms that are resistant to treatment. Rare cases eczema
- Often vague like abdominal pain
- Not associated with food contact as presentation delayed
- Can mimic other diseases e.g GORD and colic
What are some specific food allergy disorders that are IgE mediated and what foods are common triggers of these disorders?
PFS doesn't cause any GI symptoms as the heat and acid of the stomach destroy the pollens allergenicity
What are some specific food allergy disorders that are Non-IgE mediated and what foods are common triggers of these disorders?
FPIES: can cause possible shock due to vomiting and diarrhoea in 25% of cases. Often to milk, soya, rice, wheat and meat
What are food allergy presentations influenced by?
- Age (food allergy march)
- Effects of processing
- Allergen cross reactivity
At what age do different food allergies usually present?
Changes as childs diet becomes more diverse
Improving allergies: milk, egg, wheat, fruit
Persisting allergies: peanut, tree nut, seed, fish and shellfish
What are some examples of how high temperature and food matrix (mixing with other foods) can change allerginicity of a food type?
Wheat: boiled doesn't change but matrixing with wheat decreases allerginicity
Egg: cooked egg less allergic so baked egg used to test allergy and resolve it
Apple: pollen labile so not a problem if processed
How does food processing lower the allerginicty of foods in some cases?
Epitopes can no longer be recognised by the IgE antibodies
When a child is diagnosed with a food allergy, what do they need to be warned about?
Cross reactivity, could also be allergic to other substances with similar proteins (see image)
e.g would test for all nut allergies if indiviual present with single nut allergy as high cross-reactivity
How do we diagnose a food allergy in general?
- Medical history
- Physical examination
- Screening tests
- Diagnosis verification
What are some important questions to ask in the medical history when trying to diagnose a food allergy?
- Context of reaction
- Presenting symptoms
- Food considerations
On a physical examination for a potential food allergy, what two things should be done?
- Identify manifestations of food allergy as often present in outpatient after symptoms
- Differential diagnosis with other allergic conditions e.g. eczema and asthma
- Take weight and height of child to observe trends to see if they find it difficult to gain weight
What are some screening tests that can be done for food allergies?
- Test selection depends on clinical history and possible cross reactivity (don't test for all allergens!!)
IgE mediated presentation (need to prove sensitisations)
- Skin prick test (15 mins)
- Prick prick tests for foods that blood test isn't available
- Blood specific IgE
- Elimination diet
What does detecting the presence of IgE confirm?
- Sensitivity not allergy
- Level of IgE correlates with likelihood of allergy but does not correlate or predict severity of allergic reaction
How can one verify a diagnosis of a potential food allergy?
Controlled oral food challenges