Food Allergy Flashcards
Definition of food allergy
An adverse immune-mediated response, which usually occurs when a person is exposed to a sepcific food allergen. Usually IgE mediated
What is the mechansim for non-IgE mediated food allergy, how does it present?
Cell mediated, typically occuring hours after ingestion
May present as food protein induced enterocolitis syndrome in young children- vomiting (with/without diarrhoea), abdominal cramps, colic, possible faltering growth
What types of food allergy are medaited by mixed IgE and non-IgE mechanisms
- Cows’ milk protein allergy
- Eosinophilic oesophagitis
- Eosinophilic gastroenteritis
What is ‘oral allergy syndrome’
A secondary food allergy caused by corss-reactivity between aeroallegens and fruits, vegetable and nuts
What is food intolerance
A non-immunological hypersensitivity reaction to a specific food- often presents with non-specific GI symptoms, headache fatigue etc.
What are some risk factors for food allergy
- Known food allergy
- Known atopic eczema (development of early-onset atopic ezema before 6 months of age and severe eczema below the age of one associated with development of food allergy> peanut allergy may develop by exposure to impaired skin barrier)
- Family history of atopy or food allergy
What is the prevalence of food allergy, how has it changed over time
- The prevalence of true food allergy confirmed by oral food challenge is about 3–8% in children
- There is evidence that the prevalence of food allergy has increased since the early 1990s
Common complications of food allergy
Severe and life-threatening reactions (most common trigger of anaphylaxis in the community), Stress and anxiety, social exclusion, Restricted diet and malnutrition
Presentation of food allery
- Classical symtoms which develop within seconds or minutes to 1-2 hours after ingestion of a specific trigger food, and typically resolve before 12 hours (if IgE mediated)
- Systemic symptoms- Respiratory distress, severe wheeze, hypotension, tachycardia or bradycardia, drowsiness, confusion, collapse and loss of conciousness (suggests life-threatening anaphylaxis)
- Skin- urticaria, angio-oedema (most commonly of the lips, face and around the eyes), erythema, generalised itching and sneezing
- Respiratory- presistent cough hoarseness, wheeze, breathlessness, stridor, nasal discharge, congestion, itching and sneezing
Symptoms of more severe reaction include: respiratory distress, wheeze, stridor, abdo pain, vomiting, diarrhoea, shock, collapse
Non-IgE mediated food allergy usually presents with: vomiting with or without diarrhoea, abdominal cramps, colic, possible falering growth. It may present with blood in the stool due to proctitis in the first few months of life
How might oral allergy syndrome present
Mild, transient localised urticaria with associated itching an swelling of the lips, tongue and throat. Ofetn associated with co-morbid rhinitis symptoms after ingestion of fresh fruits and vegetables
What aspects are important to ask about in a food allergy history
- Possible causal foods. The form in which the food is eaten, setting of the reaction
- Symptoms
- Frequency, speed of onset, duration, and timing of reaction in relation to eating.
- Setting of reactions
- Reproducibility of symptoms
- Weight gain and nutritional status, age at which it started and any supplemental food (breast fed etc.)
- Co-morbid atopic symptoms and FHx
Investigations for food allergy
- Examine for BMI
- Skin-prick tests are the most useful confirmatory test (may be suppressed by recent antihistamine, BB, corticosteroid use)
- Patch testing- identifies the allergens that cause reactions through delayed contact hypersensitivity (T cell mediated)- allergic extract held against skin for 48 hours
- Measurement of specific IgE antibodies
- Non-IgE mediated food allergies are harder to diagnose- more reliant on history and examination- eosinophilic infiltrates on histology is supportive of a diagnosis
- For both IgE- mediated and non-IgE mediated food allergies, the gold standard investigation in cases of doubt is exclusion of the relevant food under the dietician’s supervision
Increased size of the skin prick wheal or concentrations of serum specific IgE are associated with an increased likelihood of food allergy, but they do not predict symptom severity
Allergy testing may also be used to assess whether tolerance has developed in a person with a confirmed food allergy. The optimal interval for follow-up testing is not known, and partly depends on the specific food allergen
When should a child be referred to A&E with suspected food allergy
Arrange immediate ambulance transfer to A&E if there are systemic symptoms or suspected anaphylaxis with or without angio-oedema
Management of food allergy
Arrange referral to an allergy specialist (more urgent if at risk of anaphylaxis, if having systemic symptoms, if diagnosis is uncertain or if history of atopy or multiple food allergies)
Dietary treatment:
* Exclusion of offending food from diet
* Dietary exclusion in mother should be considered if mother is breastfeeding
* Arrange referral to a paediatric dietician if there are concerns about faltering growth, nutritional status, specific food allergen avoidance is needed, or food reintroduction is needed
Self-help + allergy action plan:
* Provide written self-management plans and training- how to recognise lables for food allergens, avoidance during travel, vaccinations etc.
* Provide Epi-Pens for home use, advise to always keep 2 doses with them (30kg = 0.3mg for single dose)
* Itchy Wheezy Sneezy
Drug treatment:
* Mild reactions (no cardiorespiratory symptoms) are treated with *non-sedating antihistamines *(loratadine)
* Severe reactions (with cardiovascular, laryngeal, or bronchial involvement) require IM adrenaline (may be given by autoinjector (EpiPen)) and salbutamol if bronchospasm occurs
When should food challenge be considered
After 6-12 months of being symptom-free consider a food challenge (in hospital if previous symptoms were severe)
