S2) Food Allergy Flashcards
Define allergy
- Allergy is an immunological hypersensitivity that can lead to a variety of different diseases via different pathomechanisms
- It has different approaches in diagnosis therapy and prevention
Is an allergy a disease?
Allergy is not a disease itself, but a mechanism leading to disease.
Define allergen
- An allergen is any substance stimulating the production of IgE or a cellular immune response.
- Usually a protein, but can be carbohydrates
Define sensitivity
Sensitivity is a normal response to a stimulus.
Define hypersensitivity
Hypersensitivity is an abnormally strong response to a stimulus.
Define sensitisation
Sensitisation is the production of IgE antibodies after repeated exposure to an allergen.
Define atopy
- Atopy is a tendency to produce IgE antibodies in response to ordinary exposure to potential allergens.
- Strongly associated with asthma, rhinitis, eczema and food allergy.
Define anaphylaxis
Anaphylaxis is a serious allergic reaction with bronchial, laryngeal and cardiovascular involvement that is rapid in onset and can cause death.
There are 8 possible presentations of allergy. Identify them
- Allergic rhinitis
- Allergic conjuctivitis
- Asthma
- Atopic dermatitis / eczema
- Urticaria
- Insect allergy
- Food allergy
- Drug allergy
Allergic rhinitis is also called hay fever. Identify its symptoms and triggers
- Symptoms: blocked/runny nose, itchy nose, sneezing.
- Triggers: pollen, pets or HDM.
Allergic conjuctivitis can occur with allergic rhinitis. Identify its symptoms
Symptoms: red, swollen, itchy, watery eyes.
Asthma is not always allergic but its symptoms are the same. Identify them
Symptoms: wheeze, cough, shortness of breath and tight chest
What is atopic dermatitis/eczema?
Atopic dermatitis is the commonest chronic inflammatory skin disease with itch and excoriation
What is urticaria?
Urticaria is an acute/chronic (±6w) maculo‐papular pruritic rash with/without angioedema
Insect allergy is usually to bee/wasp stings. What are its different forms of presentation?
- Mild (local)
- Moderate (urticaria)
- Severe (anaphylaxis)
Why is allergy important?
- Allergy is common
- Allergy is associated with significant morbidity
- Allergy can be fatal
How exactly is allergy common? Provide three examples
- Approx. 50% of UK adults have at least 1 allergy
- Allergic rhinitis affects up to 30% of adults.
- Asthma is diagnosed in more than 10% UK children
Define food
- Food is a substance, whether processed, semi‐processed or raw, which is intended for human consumption
- It is also any substance used in the manufacture, preparation or treatment of food.
Define food allergy
Food allergy is an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a food.
Define food intolerance
Food intolerance are numerous adverse responses to foods that do not involve an immune response.
What are the 3 most common food allergies?
- Milk
- Eggs
- Peanuts
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
Identify and describe the 2 types of adverse food reactions
- Non‐immune mediated: primary food intolerances
- Immune mediated: food allergy and coeliac disease
What are the two types of immune mediated adverse food reactions?
- IgE mediated
- Non‐IgE mediated
What are the characteristics of food causing non-immune mediated adverse reactions?
- Pharmacologic eg. caffeine
- Toxic eg. scromboid fish toxin
What are the host characteristics in non-immune mediated adverse food reactions?
- Psychological eg. food adversion
- Metabolic eg. lactose intolerance
For IgE-mediated food reactions, describe the following:
- Symptom onset
- Common foods
- Presenting age
- Symptom onset: immediate (5‐30 min)
- Common foods: milk, egg, nuts, shellfish
- Presenting age: variable, depends on contact
Do all IgE-mediated allergies last a lifetime?
- PFS is detected in adolescence and milk allergy by 1st year
- Milk and egg allergies can resolve while others persist into adulthood
For non IgE-mediated food reactions, describe the following:
- Symptom onset
- Common foods
- Presenting age
- Natural History
- Symptom onset: delayed (hours - days)
- Common foods: milk, soya, wheat, rice & oats
- Presenting age: infancy and early childhood
- Natural history: resolve earlier than IgE
How can IgE-mediated food allergies present in the skin?
- Pruritus, erythema
- Acute urticaria
- Acute angioedema (lips, face, eyes)
How can IgE-mediated food allergies present in the Gastrointestinal system?
- Angioedema (lips, tongue,palate)
- Oral pruritus
- Nausea, vomiting, diarrhoea
How can IgE-mediated food allergies present in the respiratory system?
- Upper resp: blocked/runny nose, sneeze, itch
- Lower resp: wheeze, cough
How can IgE-mediated food allergies present in the Cardiovascular system?
- Pallor
- Drowsiness
- Hypotension
How can non IgE-mediated food allergies present in the skin?
- Pruritis
- Eczema
- Atopic eczema
How can non IgE-mediated food allergies present in the Gastrointestinal system?
- Loose or frequent stools
- Blood and/or mucus in stools
- Abdominal pain
- Food refusal/aversion
- Constipation
Identify 4 different presentations of IgE-mediated adverse food reactions
- Acute urticaria/angioedema
- Anaphylaxis
- Pollen‐food syndrome (PFS)
- Food‐associated exercise‐induced anaphylaxis
When does Food‐associated exercise induced anaphylaxis occur?
- Food triggers anaphylaxis only if ingestion is followed temporally (within 2 hours) by exercise.
- Involves wheat, shellfish, celery
Identify some symptoms of Pollen Food Syndrome.
What is it associated with?
- Symptoms: pruritus and mild oedema confined to the oral cavity
- Associated with hay fever (raw fruit and vegetables)
Provide 4 examples of non-IgE mediated adverse food reactions
- Proctocolitis
- Enterocolitis
- Eosinophilic oesophagitis
- Food Protein induced enterocolitis syndrome (FPIES)
What is proctocolitis?
- Proctocolitis is the passage of bright red blood in mucousy stools in otherwise asymptomatic infants.
- Involves reactions with breastmilk
Enterocolitis involves multiply variable GI symptoms. Identify them. Which food is it associated with?
- Symptoms: feed refusal, persistent vomiting, abdominal cramps, loose stools and constipation
- Associated with milk, eggs, wheat
Identify the symptoms involved in eosinophilic oesophagitis. Which food is it associated with?
- Symptoms: oesophageal inflammation and scarring, feeding disorders, reflux symptoms, vomiting, dysphagia
- Involves milk, eggs, wheat
What are the symptoms of Food protein‐induced entero‐ colitis syndrome?
- Profuse vomiting leading to pallor, lethargy and possibly shock
- Diarrhoea in 25%
Who is affected in Food protein‐induced entero‐ colitis syndrome?
Which food is involved?
- Primarily affects infants.
- Involves milk, soya, rice, wheat, meat
The Food allergic march refers to the change in food allergies with increasing age. Illustrate this with reference to:
- Infancy
- Childhood
- Adolescence
- Infancy: milk, eggs, peanuts
- Early childhood: soya, wheat, tree nuts, fish, kiwi, sesame, shellfish
- Adolescence: fresh fruit and vegetables
Explain the effect of high temperature in milk allergy sufferers
- Casein is more heat resistant than whey
- Availability & allergenicity is reduced in food matrix
- 70% milk‐allergics can tolerate baked milk (in wheat)
Explain the effect of high temperature in egg white allergy sufferers
- 75% major proteins in egg white are heat labile
- Well cooked egg is much less allergenic than raw egg
- 70% of egg‐allergics can tolerate baked egg (in wheat)
Explain the effect of high temperature in peanut allergy sufferers
- Allergenicity increases if dry roasted and decreases if boiled/fried
- Perhaps explains more allergy in Western societies vs Asian
Explain the effect of high temperature in fish allergy sufferers
Fish protein is very heat stable, but canned tuna and salmon are significantly less allergenic.
Explain the effect of high temperature in PFS sufferers
- Apple proteins are exquisitely heat sensitive
- Patients with PFS can eat processed apple
If someone is allergic to cow’s milk, what else could they react to?
92% risk they can react to goat’s milk
If someone is allergic to a tree nut, what else could they react to?
37% risk they can react to other tree nuts (walnut, brazil, cashew, hazelnuts)
If someone is allergic to a fish, what else could they react to?
50% risk they can react to other fish (salmon, swordfish and sole)
If someone is allergic to a shellfish, what else could they react to?
75% risk they can react to other shellfish (crab, lobster, shrimp)
If someone is allergic to pollen, what else could they react to?
55% risk they can react to fruits or vegetables
Identify the 4 steps involved in diagnosing a food allergy
- Medical history
- Physical examination
- Screening tests
- Diagnosis verification
Which 3 things should one gather when taking a medical history for a potential 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
- Differential diagnosis with other allergic conditions e.g. eczema
Identify and describe some IgE-mediated screening tests
- Serum specific IgE: IgE circulating in blood
- Skin prick tests: response of skin mast cells to allergens
Which investigation can one perform for both IgE-mediated and non IgE-mediated food allergy?
Elimination diet
How can one verify a diagnosis of a potential food allergy?
Controlled oral food challenges
What should one ask about context of a reaction in a medical history for a food allergy?
- Age of onset.
- List of all suspected foods causing symptoms
- Route of exposure (ingestion, skin contact, inhalation).
- Activity at time of exposure (exercise/alcohol)
What should one ask about a patient’s symptoms in a medical history for food allergy?
- Severity, timing and duration of symptoms
- Symptom onset after food exposure.
- Treatment provided and response
What should one consider about food when taking a medical history for a food allergy?
- Food preparation (cooked, raw, added ingredients)
- Minimal quantity of food exposure required to cause symptoms
Outline the 3 steps involved in an immunoassay for detection of specific IgE
- Allergen is absorbed and immobilised to a solid phase.
- Patient’s serum is added followed by incubation
- Allergen‐bound IgE is detected by an enzymatically labeled anti‐human IgE monoclonal antibody
What are the most commonly used techniques for immunoassays for IgE antibodies?
- ELISA‐Plates
- Western blots
- Microarrays
Identify three steps in active management of food allergies
- Anticipatory allergy testing
- Dietetic advice for dietary exclusions
- Prescription of emergency medication
What are the 2 steps involved in anticipatory allergy testing?
- Test for cross‐reactive allergens to minimise dietary exclusions.
- Test for known potential future food allergens i.e. peanut in egg allergy
Explain how re-introduction and desensitisation can also be used in the active management of food allergies
- Re‐introduction of foods where allergy known to resolve
- Desensitisation to food allergens e.g. use baked milk or baked egg in re‐introductions
How are skin prick tests and serum IgE blood tests used?
- Determine presence of sensitivity not allergy
- Level of sIgE / size of SPT correlates with likelihood of allergy and not severity
