paediatric allergy Flashcards
IgE mediaed allergy pathophys
allergen prested to T cell
B cell activated
bind to mast cells
sensitisation
mast cell exposed to allergen
bursting of mast cell releases inflammatory mediators
exposure to allergen
mast cell degranulation
rapid release and onset of symptoms
histamine, tryptase, hydrolase
later realease of inflammatory mediators - prostaglandins, leukotrienes, cytokines
what does histamine cause
- bronchial smooth muscle contraction
- vasodilation
- separation of endothelial cells (hives)
- pain and itching
genetic influence to allergy
parental atopy (maternal) concordance for allergy in twins
hygiene hypothesis
too clean
children in farmyard environments less allergies/sensitisation
is it allergy?
rapid onset histamine mediated reactions urticaria, erythema, andioedema, pallor/sweating, wheeze improvement with antihistamines relatively quick resolution of symptoms
what caused the reaction?
food environmental allergen drug sting/bite idiopathic
common food allergies
cows milk hen's egg peanuts tree nuts e.g. walnuts soya wheat fish sesame
mild/moderate reaction
angioedema (not involving airway)
urticaria and rash
severe reactions
andioedema of airway (stridor)
bronchospasm
hypotension
supporting evidence that it is an allergy
prev reactions atopy FHx response to Rx co-existing asthma
allergy investigations
skin prick testing
specific IgE - blood test
oral food change
skin-prick testing pros
easy to do
non-invasive
immediate results - 20min
negative SPT very likely not allergy
skin prick testing cons
stop antihistamine 48hrs prior broken skin theoretical risk of reactions dermatographism over-interpretation +ive results avoid random tests
specific IgE pros
no need to stop antihistamines
no risk of reactions
specific IgE cons
expensive invasive delay in obtaining results less sensitive and specific than SPT highly unreliable results in eczema
oral food challenge
day case procedure
gold standard
what actually happens upon contact or ingestion?
invenstigating urticaria and angioedema
urticaria only with no trigger - none, consider SPT/IgE is sus food/environmental trigger
angioedema only - look for hereditary angioedema C4 and C1 esterase inhibitor
rarely: FBC, urinalysis, ESR, LFT, coeliac screen, TFT
treatment of allergies
avoid triggers H1 antihistamine preventative: high dose antihistamines leukotriene antagonist corticosteroids tranexamic acid anti IgE monoclonal antibody (omalizumab) in kids >7yrs
anaphylaxis features
laryngeal oedema hypotension collapse bronchospasm feeling of impending doom onset usually in mins
anaphylaxis onset of symptoms
within 60mins
later the onset the less severe the attack
risk factors for anaphylaxis
poorly controlled asthma stress exercise viral infection alcohol
adrenaline pen
adult 0.3mg, junior 0.15mg
1st line rx anaphylaxis
early use assoc with better outcomes
