Allergy Flashcards
Type 1 hypersensitivity?
Immediate
IgE mediated - allergen binds to IgE on basophils/mast cells causing degranulation and inflammation
Anaphylaxis, Urticaria, angioedema, asthma, rhinitis
Type 2 hypersensitivity?
Sub-acute
Antibody-dependant cytotoxic - IgG/M/A attacks antigen on cell surface and complement pathway activated
Haemolytic anaemia, Goodpasture, blood transfusion reaction, myasthenia, graves
Type 3 hypersensitivity?
Sub-acute
Immune complex - Ag-Ab complexes deposit in tissues and activate complement/inflammation
SERUM SICKNESS LIKE REACTION
SLE, GN, HSP
Type 4 hypersensitivity?
Cell mediated
Lymphocyte - cytokine release
Contact dermatitis, transplant rejection, TEN/SJS
When is an IgE specific allergen test indicated?
Confirmation of IgE mediated food allergy
Determine if safe to proceed to oral food challenge
When is IgE specific food allergen test NOT indicated?
If tolerating the food without an IgE reaction (eg eczema)
Food “intolerance”
Non-IgE mediated reaction (FPIES)
Chronic idiopathic urticaria
What medication to withhold prior to skin prick testing?
No antihistamines for 3-5 days
No tricyclic antidepressants or antipsychotics for 7 days
Factors influencing skin prick result?
Certain medications - antihistamines, amitriptyline, olanzapine
Dermatographism
Recent episode of anaphylaxis
Positive skin prick test and positive hx?
Confirmation of food allergy
Negative skin prick test and positive hx?
Proceed to food challenge
What is most common use of CRD test? When not to do?
Peanut
Don’t do if high ARA H 2
Definition of anaphylaxis?
Skin features AND resp/cardio/GI sx OR hypotension
Can still consider anaphylaxis if hx suggestive if skin features not present
Insect bite anaphylaxis?
GI sx alone is sufficient for adrenaline
Most common food allergy?
Egg
Most common anaphylactic allergy?
Peanut, tree-nut, milk
Risk factors for fatal anaphylaxis?
Adolescent age
Nut/shellfish trigger
Poorly controlled asthma
Treatment delay
What not to do when child has anaphylaxis?
Let them stand or walk -> HIGH RISK OF DEATH
Which allergens is child likely to outgrow or not outgrow?
Nuts and seafood - tends to persist
Egg, wheat, milk - vast majority outgrow
Risk factors for allergic rhinitis?
FHx Smokers in family High IgE Indoor allergens LUSCS
Severe allergic rhinitis?
Sleep disturbance or school interruption
Prevalence of eczema?
10-30% worldwide; 80% outgrow by age 5
Pathophys of eczema?
Defective barrier
- keratinocytes induce cytokines
- filaggrin mutation in 50% of severe eczema
- SPINK5 mutation in netherton (severe eczema syndrome)
Immune dysregulation
- Increased Th2 cytokines
Environmental factors influencing eczema?
1 Environmental irritants (all pts) 2 Infections (all patients) - staph colonisation producing superantigen TH2 response 3 Airborne (some pts) - dustmites 4 Food (some pts) - 40% have co-existing food allergy
Eczema treatment pillars?
Manage triggers
Reduce inflammation
Treat super-infections
AEs of topical corticosteroids in eczema treatment?
Peri-oral dermatitis
Striae if used in striae prone areas
Theoretical suppression of HPA
YEs of topical pimecrolimus in eczema?
Application area burning
Irritation, pruritus, erythema
Skin infections
Desquamation (rare)
Peri-oral dermatitis VS eczema?
Peri-oral dermatitis:
- zone of sparing around lips
- occurs as rebound following corticosteroids
- treated with erythropoietin/tetracycline
- is a variant of rosacea
Treatment of large local reaction to insect bite/sting?
Cold compress Oral prednisolone NSAID for analgesia Antihistamine for pruritis RISK OF SYSTEMIC REACTION IN FUTURE IS 7%
Most common conjunctivitis and is assoc w allergic rhinitis?
Allergic conjunctivitis?
Conjunctivitis of upper tarsal plate, long eyelashes and worse in spring/summer?
Vernal conjunctivitis
Conjunctivitis of lower tarsal plate in late adolescent with atopic dermatitis?
Atopic conjunctivitis
Giant papillae in contact lens wearer?
Giant papillary conjunctivitis
Serum sickness pathophysiology?
Type 3 hypersensitivity reaction
Ag-Ab complexes, intermediate size deposit in vessels
Signs/symptoms of serum sickness/serum sickness like reaction?
Fever, rash, poly arthritis/arthralgia
Most common drug cause of serum sickness like reaction?
Cefaclor
Investigation findings in serum sickness/SSLR?
Low plts and neuts
High ESR and CRP
Urinanlysis - proteinuria, haematuria
Low C3 and C4 and low total haemolytic complement (CH50)
