Food Allergy Flashcards
Allergy is a mechanism leading to disease.
Define;
- Allergen
- Sensitivity
- Sensitisation
- Atopy
Allergen: Any substance stimulating IgE production/ a cellular immune response. Usually proteins
Sensitivity: Normal response to a stimulus
Sensitisation: Production of IgE ABs after repeated exposure to an allergen
Atopy: Personal/ familial tendency to produce IgE in response to exposure to potential allergens. (Strongly associated with Asthma, Hayfever, Eczema and food allergy)
List 3 reasons why Allergy is important
- Allergy is common (Hayfever affects 30% of adults, More than 10% of children have Asthma, 6% of children have food allergy)
- Allergy is associated with significant morbidity (Impaired sleep and daytime function/ productivity/ school performance, impact on social life)
- Allergy can be fatal (Every year 1200 people die from Asthma in UK)
List 8 Allergic CONDITIONS
- Allergic Rhinits/ Hayfever
- Allergic Conjuctivitis
- Allergic Asthma
- Eczema/ Atopic Dermatitis
- Urticaria/ Hives
- Insect allergy
- Drug allergy
- Food allergy
Describe the Presentation and list 3 Triggers of Allergic Rhinits
- Itchy nose/ Sneezing
- Blocked/ Runny nose
- Pollen
- Pets
- House dust mites
Describe the presentation of Allergic Conjunctivitis
- Red, swollen, watery, itchy eyes
- Occasionally occurs with Allergic Rhinitis, so has similar triggers
(The itchiness is a key symptom that allows AC to be distinguished from other forms of Conjunctivitis)
Describe the presentation of Allergic Asthma
Are allergens common triggers for asthma attacks?
- Asthma symptoms (wheeze, cough, tight chest, SOB)
- Allergens are NOT common triggers for asthma attacks
Describe the presentation of Eczema/ Atopic Dermatitis
(This is the commonest chronic inflammatory skin disease)
Describe the effectiveness of allergen avoidance
- Itchy skin-> Scratching-> Chronic skin changes
- Triggers are rarely recognised and allergen avoidance rarely provides symptomatic improvement
Describe the presentation of Urticaria/ Hives
- Acute or Chronic (< or > 6 weeks)
- Maculopapular pruritic rash
- With or without Angioedema
Describe the presentation of Insect allergy
- Mild (localised skin reaction- Swelling + Itch)
- Moderate (Urticaria)
- Severe (Anaphylaxis)
Describe Drug and Food allergy
Drug allergy: Much less common than reported by patients
Food allergy: Varying symptom presentation + severity
Allergic disease evolve in a characteristic manner with age. This change is called the Allergic March
Give 3 examples
- Eczema + Food allergy are predominant in children and decrease in incidence as age increases and they improve spontaneously
- Asthma is predominant in children, then improves in many and decreases in prevalence to adult levels
- Rhinitis + Conjunctivitis are rare in children, then increase in prevalence in adulthood
What are the 2 broad types of Food allergy?
How does Food Intolerance differ to Food Allergy?
Anyone can be allergic to anything. List the 3 most common food allergies
- IgE-mediated
- Non-IgE mediated
- Food intolerance does not involve the immune response
- Milk, Eggs, Peanuts
List the 2 types of Adverse Reactions to foods
- Non-immune mediated (primary food tolerances);
- Due to Food characteristics or
- Due to Host characteristics - Immune mediated (Food allergy or Coeliac disease);
- IgE mediated or
- Non-IgE mediated
Describe how Food Characteristics can lead to Non-immune Mediated Adverse Reactions to food
- Reactions to pharmacologically active food components (Caffeine)
Illness in response to;
- Toxins from microbial contamination
- Scromboid fish toxin (Excess histamine from decayed/ spoiled fish-> symptoms similar to allergy)
Describe how Host Characteristics can lead to Non-immune Mediated Adverse Reactions to food
- Metabolic disorders (Lactose intolerance)
- Psychological/ neurological responses (food aversion or rhinorrhoea due to spice)
Compare IgE and Non-IgE Mediated food allergy in terms of;
- Symptom onset
- Common foods
- Presenting age
IgE;
- Immediate (5-30mins)
- Milk, eggs, peanuts, fish/ shellfish, fruit + veg
- Depends on age of contact
Non-IgE;-
- Delayed (hrs-days)
- Milk + soya, wheat, FPIES: milk, soya, rice, wheat, meat
- Infancy and early childhood
All milk allergies present by what age?
Same for IgE and Non-IgE mediated
12 months
Compare IgE and Non-IgE Mediated food allergy in terms of;
- Systems affected
IgE;
- Skin, GI Tract, Respiratory, CVS
- Can also have behavioural changes (Mood changes, agitation, ‘sense of impending doom’)
Non-IgE;
- GI tract mainly (often multiple and resistant to medication)
- Rarely, skin (Itch, Eczema)
Describe how IgE mediated food allergy affects the Skin
- Itch
- Reddening
- Local/ Generalised Urticaria
- Angioedema (lips, face, eyes)
Describe how IgE mediated food allergy affects the GI tract
- Angioedema (lips, tongue, palate)
- Oral itch
- Colicky ab pain
- Nausea, Vomit, Diarrhoea
Describe how IgE mediated food allergy affects the Respiratory system (upper and lower)
- Usually within skin and/or GI symptoms
- Upper Respiratory: Runny/ blocked nose, Sneeze, Itchy nose, Croupy cough, Stridor
- Lower Respiratory: SOB, cough, wheeze
Describe how IgE mediated food allergy affects the CVS
- Uncommon in food allergy and rarely alone
- Pallor, Drowsy, Hypotension
List 3 reasons Non-IgE mediated food allergy symptoms can be attributed to being due to other conditions
- Can be vague (ab pain)
- Not clearly associated with food contact (delayed)
- Can mimic common GI conditions (GORD in infants)
List 4 presentations of IgE mediated food allergies
- Urticaria/ Angioedema (hives with swelling, N+V)
- Anaphylaxis
- Pollen-food Syndrome (PFS)
- Food-associated exercise induced anaphylaxis
Describe Pollen-Food Syndrome (PFS)
- Itch + Mild oedema of Oral Cavity (lips, tongue, mouth, throat)
- Usually associated with Hayfever
Describe Food-associated exercise induced anaphylaxis
Food triggers anaphylaxis if ingestion is followed by exercise within 2 hours/ temporarily
List 4 presentations of Non-IgE mediated food allergies
- Proctocolitis
- Enterocolitis
- Eosinophilic Oesopagitis
- FPIES, Food protein induced enterocolitis syndrome
Describe Proctocolitis
- Bright red blood in mucousy stool
- In asymptomatic infant
Describe Enterocolitis
- Food refusal
- Persistent vomiting
- Ab cramps
- Loose + frequent stools
- Constipation
Describe Eosinophilic Oesophagitis
- Symptoms from Oesophgeal inflammation + scarring
- Feeding disorders
- Reflux
- Dysphagia
- Food impaction
Describe FPIES
Caused by milk, soya, rice, wheat, meat
- Primarily in infants
- Profuse vomiting-> Pallor
- Lethargy
- Possibly shock
- Diarrhoea in 25% of cases
What’s the main influence on the age at which food allergies present?
Name the most common food allergy in adults
Individual’s diet
Pollen-food Syndrome, PFS
Describe the aetiology of PFS
- Usually manifests in teenage years
Result of cross-reactivity between pollens;
- Of fruit, vegetables and nuts
- and those causing hayfever
(Heat and stomach acids easily denture these allergens, so symptoms occur only with unprocessed food that has had mucus contact)
The ability of allergens to induce symptoms is influenced by their Epitope structure which affects their heat stability.
Compare Sequential and Conformational Epitopes
Sequential;
- Not damaged by heat= heat stable
Conformational;
- Altered/ destroyed by heat= Lose allergenic potential
Casein and Whey are 2 components of milk.
Which is more heat resistant/ stable?
Casein
Why can Baked Milk (in biscuits) be used to reintroduce milk into the diet of someone who’s milk allergy is expected to resolve?
Can heating raw milk have the same effect?
Baked milk has lower allergenicity and availability to the immune system
Not sufficiently for clinical use
Egg whites contain 5 main proteins.
Which of these 5 is heat stable/ resistant?
Why is this clinically important?
- Ovomucoid (comprises 10% of the proteins)
- Hard boiled/ well cooked scrambled eggs have 80-90% les allergenicity than a raw one
- Baked eggs further reduce the allergenicity
- Thus, baked eggs are used as the initial food in assessing + treating a resolving egg allergy
How can peanut allergenicity be increased and decreased?
To increase: Use dry/ roasted peanuts
To decreases: Use boiled/ fried peanuts
(Explains why western countries have more peanut allergy prevalence)
Fish proteins are very heat stable.
List 2 variants that are a lot less allergenic
Canned Tuna and Salmon
Apple proteins are very heat stable.
What kind of apple can be eaten by PFS patients safely?
Processed apple
In an individual allergic to cows milk, what’s the chance of them being allergic to Goat’s milk?
92%
List 4 steps in diagnosing food allergy
- Medical history
- Physical examination
- Screening tests
- Diagnosis verification
What are 3 components of a medical history investigating food allergy?
Context of reaction;
- Age of symptom onset
- List of all suspected foods
- Route of exposure
- Activity at time of exposure
- Intercurrent illnesses at time of of exposure
- List of foods eaten previously without symptoms
Presenting symptoms;
- Observed symptoms + severity
- Timing of symptoms in relation to exposure
- Duration of symptoms, treatment provided, response to treatment
Food considerations/ detail about food ingested;
- Minimal quantity of food required for symptoms
- Manner in which food was prepared
What are 3 components of a physical examination investigating food allergy?
- Identify manifestations of allergy
- Include height and weight in children, observe trends
- Examine for other allergic conditions and differential diagnosis
What are the components of screening tests investigating food allergy?
- Skin prick tests, SPTs (Info within 15 mins)
- Blood specific IgE
- Elimination diet
How is a food allergy diagnosis verified?
Oral food challenges
Describe the use of Serum Specific IgE tests in screening for food allergy
- Tests for IgE antibodies determine the presence of Sensitivity NOT allergy
- Size of SPT wheal/ Specific units of IgE correlates with increased likelihood of allergy
List 6 methods of management of food allergy
- Anticipatory allergy testing
- Dietetic advice for dietary exclusions (Dont avoid food classes, only specific foods)
- Prescription of emergency medication
- Early food introduction in infancy (lower allergenicity food variants)
- Desensitisation to food allergens
- Oral food challenges for diagnostic verification
Describe Anticipatory Allergy testing
Patients tested for;
- Cross-reactive allergens
- Potential future allergens
How is milk allergy managed in a breastfeeding infant
- Extensive Hydrolysed formula
- If not working, Amino-acid formula
- Soya can be used after 6 months of age
As child grows up, give dairy-free weaning advice and later attempt milk re-introduction using the ‘Milk ladder’
