Transcript Food Allergy By Dr Rowan Brown

Food Allergy
By Dr Rowan Brown
Problem
Common - (1.6 - 8% of population)
Attitude - Medical vs Common Opinion
Service Provision - access to specialist opinion +
testing
Doctor’s Agenda
nutritional adequacy of child
quality of life
parental anxiety
Allergic Types
IgE (Type 1 hypersensitivity)
“Classic” Peanut Allergy
Atopy & anaphylaxis (rapid 20mins -2hrs)
non-IgE (IgG)
examples - coeliac disease
non-specific + delayed symptoms
Intolerance
multiple types - common: lactose intolerance
IgE - mediated
allergy
Food
Age of onset
Resolution
Hen’s Egg
6-24mths
7yr (75%)
Cow’s Milk
6-12mths
5yr (76%)
5yr (20%)
Peanut
6-24mths
Fish
childhood
persistent
Shellfish
adulthood
persistent
Wheat
6-24mths
5yr (80%)
Soya
6-24mths
5yr (70%)
Kiwi
Any Age
not known
IgE - mediated
allergy
Presents with multi-system involvement
urticaria, angio-oedema, rhinitis, cough,
eczema vomiting, diarrhoea, abdominal pain,
rapid onset
High association with atopy: ⇒ if present
indicates higher likelihood of anaphylaxis
Associated with multiple allergies
IgE - Diagnosis
4 modalities
History (very important)
IgE-specific titres (CAP-RAST)
Skin prick testing (SPT)
Food Challenges
Tests are sensitive, but have poor specificity,
however, in conjunction with positive predictive
values and post test probabilities a diagnosis
can be made in 70% of cases
IgE Allergy Treatment
Treatment entails elimination of food stuffs
Oral challenge (depending upon natural history
of allergy and severity of reaction)
Advice about anaphylaxis + treatment of
associated atopy (asthma)
legal vs medical assessment for anaphylaxis
prophylaxis
If every child with wheeze treated, (IM
adrenaline +
training/antihistamine/bronchodilator) the
cost per life saved calculated at $20,000,000
Non-IgE Allergy
Onset typically delayed (4-48hrs), and thus
poor association with precipitants.
IgG testing not specific with poor concordance all food stuffs will develop an IgG response.
Exceptions to this include coeliac disease with
tissue transglutaminase having a high
specificity
Management with elimination diets + if
necessary food challenges (under medical
surveillance if reaction severe)
Unclear association with IBS
Intolerance
Not an immune response
Common - Lactose intolerance.
Inability to hydrolyse lactose to
monosaccharide
Results in bloating, diarrhoea, abdominal
pain -develops several hours after
indigestion
Enterases in gut facilitate hydrolysis. May
become functionally inactive post-infection or
congenitally missing. It is common post
Cow’s Milk Allergy
Presents with an acute IgE and delayed IgG
response.
Typically occurs post breast feeding and
introduction of milk - 4-6mths
Mild symptoms may be managed with an
elimination diet, with eHF (extensively
hydrolysed formula) or AAF (amino acid
formula) - in severe cases
Challenge at 9-12mths
Breast feeding thought to be protective, though
inconclusive evidence: current ongoing trial
References
Wikipedia “Food Allergy” & “Intolerance”
Arch Dis Child 2007;92:902-908 Guidelines for the diagnosis and
managment of cow’s milk protein allergy in infants. Yvan Vandenplas
etal.
N Engl J Med 2008;359:1252-60 Food Allergy. Gideon Lack
Clin & Exp Imm;55:378-386 Clinical Immnology Review Series: An
approach to the patient with allergy in childhood. R Sporik et al