1. Allergies Flashcards
define allergy
an immunological hypersensitivity that can lead to a variety of a different diseases via different patho-mechanisms with different approaches in diagnosis, therapy and prevention. can be IgE mediated (peanut) or non IgE (milk)
define allergen
any substance stimulating the production of IgE or a cellular immune response. Allergens are usually proteins but can be carbohydrates.
define sensitivity
normal response to a stimulus
define hypersensitivity
abnormal strong response to a stimulus
define sensitisation
Production of IgE antibodies (detected by serum IgE assay or skin
prick test) after repeated exposure to an allergen
define atopy
a personal or familial tendency to produce IgE in response to exposure to potential allergens, associated with asthma, allergic rhinitis, eczema and food allergy
define anaphylaxis
A serious allergic reaction with bronchial, laryngeal and
cardiovascular involvement that is rapid in onset and can cause death
define food
A substance, whether processed, semi-processed or raw intended for human consumption (including liquids), and any substance used in the
manufacture, preparation of treatment of food
define food allergy
A immunologically mediated adverse reaction to foods
what is allergic rhinitis or hay fever?
persistent or recurrent blocked or runnny nose, itch, sneeze. usually caused by grass or pollens or dust mites
what is allergic conjunctivits?
red, swollen, watery, itchy eyes (not usually itchy is viral/bacterial), occurs with hay fever
what is allergic asthma?
wheeze, cough, SOB, tight chest, due to allergens
what is atopic dermatitis/eczema?
itchy skin where when scratched leads to chronic skin changes, triggers rarely recognised and allergen avoidance such as diet control is rarely effective
what is urticaria?
AKA hives, can occur in isolation as a maculopapular pruritic or itchy rash
if more that 6 weeks = chronic, otherwise = acute
if chronic known as spontaneous a occurs without an identifiable trigger
what is an insect allergy?
due to stings from wasps or bees
can be mild which is large but localised, characterised by redness, swelling, itch or can be life threatening if anaphylactic
what is a drug allergy?
much less common
what is food allergy?
with many foods with varying symptom presentation and severity
what conditions predominantly occur pre school
eczema and food allergy (decrease in incidence with increasing age as improves spontaneously)
what condition predominantly occur in school
asthma (decreases with age)
what conditions predominantly occur as you get older, into adulthood
rhinitis and conjuctivitis
why are allergens so important?
common
associated with morbidity and mortality
define food intolerance
the numerous and frequently reported adverse
responses to foods that do not involve the immune response.
define prevalence
IgE-mediated reactions have been reported to more than 170 foods,
so one can be allergic to any food; but food allergies and hence the prevalence
estimates are limited to few foods – the commonest being milk, egg and peanuts.
The prevalence of self-reported allergy can be up to 6 times higher than
challenge proven allergy. The estimated prevalence is higher in children affecting
about 6% compared 1-2% of adults.
what are the two classifications of adverse reactions?
non immune mediated/primary food intolerance -
food related: to the pharmacologically active food component or illness in response to toxins from microbial contamination or scromboid fish toxin (from eating spoiled oily fish where excess histamine produced from fish decay produces symptoms similar to allergy
host related: metabolic disorders such as lactose intolerance, psychological or neurological responses such as food aversion or rhinorrhea from spicy foods
- immune mediated/food allergy/coeliac disease - IgE or non IgE mediated
contrast the phenotypes of IgE mediated and non IgE mediated allergies
Feature: IgE mediated Non-IgE mediated Symptom onset: Immediate – 5-30 min Delayed – hours to days Common foods: Milk and eggs Peanuts and tree nuts Fish and shellfish Fresh fruit and vegetables VERSUS Milk and soya Wheat Milk, soya, rice, wheat and meat in FPIES Presenting age: Depends on age of contact. Pollen-doo syndrome in adolescents All milk allergy by 1 year, VERSUS Infancy and early childhood. All milk allergy by 1 year. Natural history Milk and egg allergy can resolve. Others tend to persist. VERSUS Favourable prognosis, with resolution before IgE mediated. Systems affected Skin Gastrointestinal tract Respiratory system Cardiovascular system VERSUS Gastrointestinal tract. Possibly causes eczema.
what are the stereotypical symptoms associated with IgE mediated food allergy?
a. Skin: pruritus, erythema, urticaria or
angioedema (mostly of lips, face and eyes).
b. Gastrointestinal symptoms: Angioedema of lips, tongue and palate and oral pruritus. Colicky abdominal pain. Nausea, vomiting and diarrhoea.
c. Respiratory system (usually with skin and/or gastrointestinal symptoms):
upper respiratory symptoms of runny and/or blocked nose, sneezing and itchy nose, croupy cough, stridor; lower respiratory symptoms of breathlessness, cough and wheeze.
d. Cardiovascular symptoms (uncommon in food allergy and rarely alone):
pallor, drowsy and hypotension
can also have mood changes (quiet, anxiety), agitation and a ‘sense of impending doom’
what are some difficulties associated with the presentation of non IgE mediated allergies?
vague (e.g. abdominal pain), not clearly associated with the food contact (i.e. presentation delayed) and can mimic other common gastrointestinal conditions (e.g. colic, gastro-oesophageal reflux in infants). The symptoms predominantly affect the gastrointestinal tract are resistant to medication e.g. reflux.
which disorders are associated with IgE mediated allergies?
Urticaria/angioedema: alongside Gastrointestinal symptoms of nausea and repeated vomiting. Anaphylaxis: respiratory and possibly cardiovascular symptoms (nuts, fish, shellfish, milk, egg).
Food-associated exercise induced anaphylaxis: if ingestion is followed temporally (within 2 hours) by exercise (wheat, shellfish, celery).
Pollen food syndrome: Pruritus and mild oedema of the oral cavity (lips, tongue, mouth and throat) . Usually associated with hay fever (uncooked fruit, vegetables and nuts).
which disorders are associated with non IgE mediated allergies?
Proctocolitis: Passage of bright red blood in mucousy stool in an otherwise asymptomatic infant (milk, even through breast milk).
Enterocolitis: Multiple and varying gastrointestinal symptoms including feed refusal, persistent vomiting, abdominal cramps, loose and frequent stools and constipation (milk, eggs, wheat).
Eosinophilic oesophagitis: Symptoms from oesophageal inflammation and
scarring of feeding disorders, reflux symptoms, dysphagia and food impaction (milk, egg, wheat).
Food protein induced enterocolitis syndrome (FPIES): profuse vomiting leading to pallor, lethargy and possibly shock; diarrhoea occurs in about 25% (milk, soya, rice, wheat, meat)
in terms of diet, how may allergies differently present from infancy to childhood?
infancy - less diverse diet
what is pollen food allergy and when is most common?
- adulthood, manifests in adolescence
results from the cross reactivity between the pollens of fruit, veg and nuts and pollens causing hayfever such as birch - heat and enzymes usually denature these allergens in the body so symptoms only occur in unprocessed food where food has had mucosal contact
give some examples of allergies that improve and which persist
improve - milk, egg, wheat, fruit
persist - peanut, ree, nut, seed, shellfish
what are the effects of high temperatures and food matrix on food proteins?
The ability of food allergens to induce symptoms is influenced by their epitope
structure and consequent heat stability. Allergens comprising sequential epitopes
that are not damaged by heat tend to be heat stable, whilst those dependent on the
three-dimensional structure of the protein, conformational epitopes, will be altered
or destroyed by heat and lose their allergenic potential.
Protein interactions with other ingredients such as proteins, fats and sugars in
processed foods are also important, in general resulting in decreased availability of
protein for interactions with the immune system.
eg: milk and egg
what are cross reactive allergens?
food families that share proteins so if individual allergic to say peanuts, likely to be allergic to other nuts
how are food allergies diagnosed?
history
physical exam
screen tests
how is a history of a food allergy taken?
• Age of symptom onset
• Complete list of all foods suspected in causing the symptoms.
• Route of exposure (i.e. ingestion. Skin contact, inhalation).
• Activity at the time of exposure. Exercise or alcohol can potentiate
reactions
• Any intercurrent illness at he time of the reaction because illness can potentiate a reaction or might mimic a reaction.
• List of foods eaten previously without symptoms. It is unlikely that a child can eat a food without symptoms and then develop allergy -with the exception of Pollen Food Syndrome.
Presenting symptoms.
• All observed symptoms and their potential severity. Ask all symptoms
from each system i.e. skin, gastrointestinal tract, upper and lower respiratory tract, cardiovascular system and central nervous system.
• Timing of symptoms in relation to food ingestion i.e. immediate or delayed.
• Duration of symptoms, treatment provided and the response to treatment.
c. Details about food ingested.
• Minimal quantity of food exposure required to cause symptoms.
• Manner in which food was prepared (cooked, raw, added ingredients).
how is physical examination carried out?
height and weight in children and comparison with previous weights to observe trends
examine for concomitant allergic conditiions - eczema, allergic rhitis, asthma
what screening tests are available for allergy diagnoses?
skin prick test - IgE mediated food allergy (quick, easy)
serum IgE antibodies - sensitivity not allergy (although as get higher, more likely to be allergic
diagnosis can be verified with oral food challenges
how do we manage food allergies?
- Anticipatory allergy testing. At presentation patients are tested for crossreactive allergens and potential future allergens to minimise dietary exclusions.
- Dietetic advice for dietary exclusions
- Prescription of emergency medication where indicated.
- Early food introductions in infancy. This is central to active management where lower allergenic forms of foods e.g. baked milk or baked egg are introduced early as exposure will enhance further tolerance.
- Desensitisation to food allergens. In children with milk and egg allergy that does not resolve as expected, treatment plans are available to attempt to induce
tolerance or desensitise these patients and thereby ‘cure’ these allergies. This treatment is also be available for peanut allergy but as yet not widely available
for clinical practice. - Oral food challenges for diagnostic verification.
