S1: clinical allergy Flashcards
Define allergen
Any substance stimulating the production of IgE or a cellular immune response
Usually proteins, but not always eg. carbs
Compare sensitivity vs hypersensitivity
Sensitivity = normal response to a stimulus Hypersensitivity = abnormally strong response to a stimulus
Define allergy
Hypersensitivity reaction initiated by a specific immunological mechanism, that is IgE-mediated or non-IgE mediated
Define anaphylaxis
Serious allergic reaction with bronchial, laryngeal & cardiovascular involvement
Rapid in onset & can cause death
Describe allergic rhinitis
Hay fever
Presents with persistent or recurrent blocked or runny nose, itch and sneezing
Common symptom triggers are grass, tree pollens & house dust mites
Describe allergic conjunctivitis
Red, swollen, watery & itchy eye
Occasionally occurs with hay fever & has similar allergy triggers
Describe atopic dermatitis
Commonest chronic inflammatory skin disease
Causes scratching which leads to chronic skin changes
Recognised as an allergic condition, but triggers are rarely recognised & dietary exclusions rarely provide symptomatic treatment
Describe urticaria
Can occur in isolation as a maculopapular pruritic or itchy rash
Classified as acute or chronic based on symptom duration (<6 weeks = acute, >6 weeks = chronic)
Describe types of non-immune mediated/primary food intolerances
1) Food characteristics – reactions to pharmacologically active food components or illness in response to toxins from microbial contamination
2) Host characteristics – metabolic disorders eg. lactose intolerance or rhinorrhoea caused by spicy foods
Describe IgE mediated food allergy
Immediate symptom onset
Common foods – milk, eggs, peanuts, tree nuts, fish, shellfish, fresh fruit & vegetables
Presenting age – depends on age of contact, all milk allergy by 1 year
Natural history – milk & egg allergy can resolve, others tend to persist
Systems affected – skin, GI tract, respiratory system, cardiovascular system
Describe non-IgE mediated food allergy
Delayed symptom onset
Common foods – milk, soya, wheat, rice, & meat (FPIES)
Presenting age – infancy & early childhood, all milk allergy by 1 year
Natural history – favourable prognosis with resolution before IgE mediated
Systems affected – GI tract, possibly eczema
Outline stereotypical symptoms of IgE mediated food allergies
1) Skin: pruritis, erythema, acute localised or generalised urticaria/angioedema
2) GI symptoms: angioedema of lips, tongue, palate & oral pruritus, colicky abdominal pain, nausea, vomiting & diarrhoea
3) Respiratory symptoms: upper (runny nose, sneezing, cough) & lower (breathlessness, wheeze) symptoms
4) Cardiovascular symptoms: pallor, drowsy & hypotension
Outline stereotypical symptoms of non-IgE mediated food allergies
Vague – abdominal pain
Not clearly associated with food contact, presentation is delayed
Can mimic other common GI conditions, resistant to medication
Eczema is a rare presentation
List specific disorders of IgE mediated food allergies
1) Urticaria/angioedema: acute hives with swelling & GI symptoms of nausea & repeated vomiting (any food)
2) Anaphylaxis: rapidly progressive potentially fatal multiple organ system reaction with respiratory & possibly cardiovascular symptoms (nuts, fish, shellfish, milk, egg)
3) Food-associated exercise induced anaphylaxis: triggers anaphylaxis only if ingestion is followed temporarily by exercise (wheat, shellfish, celery)
4) Pollen food syndrome: pruritis & mild oedema of oral cavity, associated with hay fever (uncooked fruit, veg & nuts)
List specific disorders of non-IgE mediated food allergies
1) Proctocolitis: passage of bright red blood in mucous stool in otherwise asymptomatic infant (milk)
2) Enterocolitis: multiple & varying GI symptoms, eg. food refusal, cramps, loose stools & constipation (milk, eggs, wheat)
3) Eosinophilic oesophagitis: oesophageal inflammation, reflux symptoms, dysphagia & food impaction (milk, egg, wheat)
4) Food protein induced enterocolitis syndrome (FPIES): infants with symptoms of profuse vomiting -> pallor, lethargy, shock (milk, soya, rice, wheat, meat)
Describe the food allergic march
Age at which food allergies present are influenced mainly by individuals diet
Natural history of food allergies vary as food allergy resolves with increasing age
Pollen food syndrome = commonest food allergy in adults
-result of cross-reactivity between the pollens of fruit, veg, nuts & pollens causing hay fever
-symptoms only occur in unprocessed food
Describe effects of high temperature and food matrix on food proteins
Ability of food allergens to induce symptoms is influenced by their epitope structure & consequent heat stability
Baked milk has lower allergenicity & availability to the immune system -> can be used to reintroduce milk back into the diet of a child
Baked egg is used as the initial food in assessing and treating resolving egg allergy
Describe implications of cross-reactive food allergens
Food families share proteins that can cause implications in an individual’s allergic manifestations
Important to be aware of which foods are related & if these have been ingested
Eg. test all nuts in an individual presenting with a single nut allergy
Describe the medical history of a patient presenting with food allergy
Context of the reaction – age of symptom onset, compete list of suspected foods, route of exposure, activity at the time of exposure
Presenting symptoms – timing, duration, severity
Details about food ingested – minimal quantity of food exposure required to cause symptoms, the way food was prepared
Describe screening tests for food allergies
Skin prick tests (SPTs) – provide info in 15 mins
-further useful as they can be used to test for foods for which there are no blood tests available by pricking the food & then the skin (prick-prick tests)
Tests for IgE antibodies – determine the presence of sensitivity & not allergy
-level of antibodies does correlate with the increased likelihood of allergy
Describe the management of food allergies
1) Anticipatory allergy testing – patients tested for cross-reactive allergens & potential future allergens
2) Dietetic advice for dietary exclusions
3) Prescription of emergency mediation where indicated
4) Early food introductions in infancy
5) Desensitisation to food allergens
6) Oral food challenges for diagnostic verification
What is the most appropriate screening test for FPIES?
Elimination diet
Which cell type is responsible for the response seen in skin allergy tests?
Mast cell
Describe type I hypersensitivity
Type 1 hypersensitivity is due to the activation of mast cells which is triggered by the antigen cross-linking IgE receptors on the surface of the mast cell
