Allergy Flashcards
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.
- Skin prick test (SPT)
- Specific IgE (previously RAST)
- 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.
IgE:
- Generalised anaphylaxis
- Pathophys: IgE induced mast cell degranulation
- Rapid onset (<2h)
- Ix: SPT/RAST, food challenge
non-IgE:
- 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
FPIES:
- 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
- FFT
Mx:
- IV fluid resuscitation
- IM adrenaline is NOT used to treat this reaction
FPIE:
- 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.
- Normal: redness, swelling up to 5-10cm, transient (resolve few to 24hrs)
- Large local reaction: swelling>10cm developing minutes to hrs after the sting and lasting over 24hrs +/- systemic upset.
- Systemic (anaphylaxis):
a. Mild – no cardiovascular sx
b. Mod/Severe – with CVS sx - 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
