Allergy Flashcards
What is atopy?
Personal and/or family tendency to produce IgE antibodies in response to ordinary exposures to potential allergens, usually proteins
Strongly associated with asthma, allergic rhinitis and conjunctivitis, eczema and food allergy
Eczema
Atopic or non-atopic
Atopic = evidence of IgE antibodies to common allergens, classed as an allergic disease
Many children have a FHx of allergy
Close relationship with food allergy (in particular egg allergy)
Screening by skin prick or IgE blood testing considered
Allergic rhinitis and conjunctivitis
Atopic or non-atopic
Underestimated cause of childhood morbidity
Intermittent or persistent and mild or severe
Temperate climates often classified as seasonal (grass, weed or tree pollen) or perennial (house dust mites and pets)
Associated with eczema, sinusitis and adenoidal hypertrophy, closely associated with asthma
Mechanism of allergic disease
polymorphisms or mutations in certain genes linked to development of allergic disease lead to susceptibility to allergy
Allergic reaction occurs when individuals make an abnormal immune response to harmless environmental stimuli, usually proteins
Developing immune system must be ‘sensitised’ to an allergen before an allergic immune response develops - sensation can be ‘occult’ meaning that sensitisation can happen even when trace amounts of food are ingested
Main stimuli for allergens
Inhalant allergens - house-dust mite, plant pollens, pet dander, moulds
Ingestant allergens - nuts, seeds, legumes, cow’s milk, eggs, seafood, fruits
Insects stings/bites, drugs and natural rubber latex
IgE mediated allergic reactions (phases)
Early phase: within minutes of exposure to allergen
- release of histamine etc from mast cells
- cause of urticaria, angioedema, sneezing and bronchospasm
Late phase occurring after 4-6 hours:
- causes nasal congestion in upper airway, cough and bronchospasm in lower airway
Allergic march
Allergic children develop individual allergic disorders at different ages:
- eczema and food allergy usually develop in infancy (often both are present) - presence is predictive of asthma and allergic rhinitis later in life
- allergic rhinitis, conjunctivitis and asthma occur most often in preschool and primary school years
- rhinitis and conjunctivitis often preceed development of asthma
Allergy Mx:
Allergy is considered a systemic disease - identify triggers to avoid and to manage children with multi-system or severe disease
Specific allergen immunotherapy can be used for allergic rhinitis, conjunctivitis, insect stings, anaphylaxis and asthma
Solutions of allergen are injected subcut or sublingual on a regular basis for 3-5y to develop immune tolerance
sublingual is safer
Major causes of childhood wheeze
viral induced wheeze
asthma
airways malacia
bronchitis
Bronchiolitis
Primary food allergy
children have failed to ever develop immune tolerance to relevant food
In infants: milk, egg and peanut
Older children: peanut, tree nut, fish and shellfish
Secondary food allergy
Children initially tolerate a food and then become allergic
Usually due to cross reactivity between proteins presents in fresh fruits/veg/nuts and those in pollens very common
milder allergic reactions than primary
itchy mouth
no systemic symptoms
S+S of IgE and Non-IgE food allergy
IgE:
- hx of allergic sx varying from urticaria to facial swelling to anaphylaxis
- 10-15 mins after ingestion
- on 1st occasion food is knowingly ingested
Non-IgE:
- D+V
- abdo pain
- FFT
- Colic
- Eczema
- Blood in stools in first few days of life from proctitis
Investigations for food allergy
Gold standard: exclusion of relevant food under dieticians supervision, followed by double-blind placebo food challenge
- child given increasing amounts of food or placebo, tiny quantity until full portion is reached
- test should be performed in hosp with resus available
IgE: skin prick tests and measurements of specific antibodies in blood (RAST test)
Non-IgE: endoscopy, intestinal biopsy, eosinophilic infiltrates = diagnosis
Mx of food allergy
avoidance of relevant foods
paediatric dietician advice to aid parents avoid allergens but also avoid nutritional deficiencies
Written self-management plans and training are essential to allow a child their family to manage an allergic attack
- antihistamines for mild attacks
- severe reaction - adrenaline given IM by an autoinjector
Causes of acute anaphylaxis
IgE mediated with significant resp or CV compromise
food allergy
insect bites
drugs
latex
exercise
inhalant allergens
idiopathic
Mx of acute anaphylaxis
ABCDE
Airway: swelling, hoarseness, stridor
Breathing: tachypnoea, wheeze, cyanosis, SpO2 <92%
Circulation: pale, clammy, hypotensive, drowsy, coma
Put patient in supine position with legs raised
Adrenaline 1:1000 give IM
If available: establish airway, high flow oxygen, IV fluids, Chlorpheniramine, hydrocortisone
Monitor: pulse ox, ECG, BP
