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Flashcards in Allergy Deck (29):

Compare: allergy, intolerance and atopy.

- Allergy: reaction initiated by specific immunological mechanisms
- IgE mediated/non-IgE mediated (T cell mediated)

- Intolerance: reaction initiated by non-immunologic mechanisms

- Atopy: genetic predisposition to become sensitised
- Produce IgE in response to ordinary exposures to common environmental allergies
- May lead to allergic disease - but not always!


Examples of intolerances

- Metabolic e.g. CHO malabsorption- lactose intolerance
- Pharmacologic e.g. Caffeine causing irritability, restlessness, palpitations
- Toxic e.g. Food poisoning- salmonella, fish toxins


Examples of atopic diseases

asthma, allergic rhino-conjunctivitis, eczema, IgE- mediated food allergy


List 3 major investigations for allergy testing, and state which is the GS.

1. Skin prick test (SPT)
2. Specific IgE (previously RAST)
3. Challenge testing (GS)


What is the process for SPT?

- Test that measures the IgE produced in vivo to an allergen
- Allergen scratched on back, with histamine and saline control
- Measure at 15 mins


What does the SPT tell you and what doesn't it tell you?

- What does it tell you?
• The larger the SPT size, the more likely an IgE mediated reaction will occur
- What does it NOT tell you
• Severity of reaction
• Non-IgE mediated reaction

- Importantly +ve SPT doesn't equal allergy, so called 'clinically silent sensitisation'


Pros and cos of the SPT?

○ Pros: readily available, inexpensive, no minimum age
○ Cons: only available to allergists


When will you get a false positive with an SPT?

- recent anti-histamines (H1 only) - withold for 3-4 days
- Recent anaphylaxis (SPT > 6 weeks later)


What is considered a +ve result with an SPT? What is a convincing result for peanut allergy?

○ +ve SPT: wheal and flare > 3mm cf saline control
○ Convincing result for peanuts - >7mm wheal


What does the specific IgE test test?

- Detects free antigen specific IgE in serum


Pros and cons of specific IgE test

- One step above, but:
○ less sensitive than SPT - more false negatives
○ More expensive
- Pros:
○ Useful if pt on anti-histamines
○ If dangerous to do SPT
○ Can use if SPT allergens not available
○ Can do a blood specific IgE e.g. to peanuts


Mx of a generalised allergic reaction: acute and ongoing

- Anti-histamines
- Cool compress
- Observation
- Identify trigger

- Allergy action plan
- Education
- Referral


What are the types of allergic rhinitis? Describe.

Seasonal allergic rhinitis:
• due to pollen allergy, esp grass in Aus
• Symptoms start abruptly in spring and continue for a variable time, depending on the geographical area.
• Symptoms are worse outdoors.

Perennial allergic rhinitis:
• usually due to house dust mite allergy, others e.g. animal dander
• Symptoms are often worse at night or early in the morning.


What are some possible consequences of serious cases of allergic rhinitis?

• increase the chance of sinus infections
• affect learning and performance in children
• lead to bad breath, a husky voice and/or a sore throat
• more frequent eye infections because people rub itchy eye


What are some clinical features of allergic rhinitis?

Nasal symptoms:
• Sneezing, itchy nose, itchy palate
• Rhinorrhoea
• Nasal obstruction - snoring, mouth breathing

Eye symptoms:
• Intense itching, hyperaemia, watering, chemosis, periorbital oedema


What Rx can be used to manage allergic rhinitis? What isn't recommended?

• Oral antihistamines (e.g. cetirizine, loratadine)
○ manage itching and sneezing or eye symptoms

• Intranasal corticosteroids (e.g. mometasone, fluticasone)
○ First line for perennial and seasonal allergic rhinitis

• Allergen immunotherapy (3-5 year program)
• NB - nasal decongestant not recommended


Compare food allergy vs food intolerance.

- Food allergy
• immune mediated
• *"Reproducible, non-dose dependent"* immunological reaction to food proteins by exposure to a defined stimulus that causes an adverse clinical reaction, at a dose tolerated by normal person

- Food intolerance - NOT immune mediated


Compare IgE vs non-IgE mediated food allergies.

- Generalised anaphylaxis
- Pathophys: IgE induced mast cell degranulation
- Rapid onset (<2h)
- Ix: SPT/RAST, food challenge

- mainly GI/skin features
- T-cell mediated
- Intermediate (2-24h)/delayed (>24h) onset
- Ix: Patch test, food challenge


What are the major food groups causing food allergies? Which are hard to outgrow?

8 major food groups cause >90% of food allergy:
• Soy
• Eggs - earliest onset
• Milk - earliest onset
• Fish
• Wheat
• Shellfish - can have later onset
• Tree nuts*
• Peanuts *

*= hard to outgrow


Outline a quick history for food allergy.

- What was ingested?
• Food type
• Form
- Amount ingested?
- How was it cooked/was it raw?
- Timing of exposure to reaction onset/offset
- How serious was the reaction? Sx of allergy?
- Treatment needed
- Previous exposures? Is it reproducible?
- FHx of allergy, PHx allergy/atopy
- High risk groups for anaphylaxis


List some conditions caused by non-IgE mediated food allergy.

- FPIES (food protein induced enterocolitis syndrome)
- FPIE (food protein induced enteropathy)
- Food protein induced proctocolitis
- Eosinophilic oesophagitis


- What age
- Which food
- Presentation
- Mx

- Weeks-months, outgrown by 3-4yo
- Common trigger cow's milk, but almost any food can
- Acutely unwell: vomiting, blood diarrhoea, CV collapse: hypotension/pallor

- IV fluid resuscitation
- IM adrenaline is NOT used to treat this reaction


- What age
- Which food
- Presentation

- Early infancy
- Cow's milk
- Unwell: vomiting, diarrhoea, oedema, FTT, abdo distention


Food protein induced proctocolitis:
- What age
- Which food
- Presentation

- Early infancy
- Cow's milk, soy milk, BF
- WELL baby - blood streaks in stool


Eosinophilic oesophagitis:
- Histopath
- Presentation
- Which food

- Eosinophilic infiltration of oesophageal mucosa
• Variable and age-dependent presenting features
• Regurgitation/vomiting
• Slow eater/food refusal
• Failure to thrive
• Difficulty swallowing
• Food impaction
• Epigastric pain
- dairy, wheat, egg, soy


Mx of Food allergies

- Education – Natural history
- Dietary avoidance
- Action plan for accidental exposure
- Consider Epipen, Medicalert bracelet
- Yearly review
- Manage and control co-morbid asthma
- Repeat SPT/RAST (12 monthly) or re-challenge 6-12mo


Describe the features of insect allergies with varying severities.

1. Normal: redness, swelling up to 5-10cm, transient (resolve few to 24hrs)
2. Large local reaction: swelling>10cm developing minutes to hrs after the sting and lasting over 24hrs +/- systemic upset.
3. Systemic (anaphylaxis):
a. Mild – no cardiovascular sx
b. Mod/Severe – with CVS sx
4. Toxic: from multiple stings, due to high concentrations of histamine-like substances.


Venom immunotherapy:
- When can one receive it
- How long is the therapy
- Risk of anaphylaxis?

- Only with evidence of:
○ specific IgE (skin or RAST test)
○ + systemic reaction with cardiorespiratory involvement.
- Induction + maintenance: 3-5years
- 10-15% experience systemic reactions during early weeks of treatment


What is important to remember regarding PHx hypotensive reaction with insect allergy?

40% will have immediate systemic allergic reaction on subsequent stings