Allergy

Question 1

What is the pathogenesis of IgE allergy (e.g. type 1 hypersensitivity reaction)? What are the effects of this reaction?

Answer 1

1. First exposure
2. TH2 activation stimulate B cells
3. Produce IgE
4. binding of IgE to mast cell FcepsilonR
5. repeated exposure
6. cross link and release mediators
7. release cytokines and histamine

Anaphylaxis:

• acute severe systemic allergic reaction
  
  • typical skin features (urticaria, erythema, flushing, angioedema)
  • respiratory compromise (tongue and throat swelling with bronchospasm)
  • CVD symptoms
  • stings - abdo pain and vomiting sometimes indicates anaphylaxis

Question 2

Go through the action plan for anaphylaxis

Answer 2

Signs of mild to moderate reaction:

• swelling of lips, face, eyes
• hives or welts
• tingling mouth
• abdominal pain, vomiting

Action for mild to moderate:

• insect sting (flick it out)
• for tick (freeze dry)
• stay with person
• locak EpiPen or Epipen Jr autoinjector
• phone family/emergency

Following signs:

• difficulty breathing/talking
• swelling of tongue
• persistent dizziness
• wheezing or cough
• pale/floppy

see hospital copies

• lie them flat - (don’t want to drop blood pressure)
• ambulance always called when adminster adrenaline
• further adrenaline doses can be administered (other medications after Epipen)
  
  • Jr - 300mcg >20kg, 150mcg <20kg
  • >12 years 500mcg

without cutaneous features could still be anaphylaxis, ventolin isn’t a treatment for anaphylaxis. If in doubt treat for anaphylaxis.

>2 adrenaline boluses notify ICU.

Question 3

What is the assessment of someone post-anaphylaxis? What investigations can you do?

Answer 3

• History:
  
  • exposure:
    
    • what
    • amount
    • cooked?
    • time of exposure
    • treatment needed?
    • previous exposures?
  • Investigations?
    
    • skin prick test
      
      • false negatives
        
        • antihistamines (withhold 3-4 if H1, H2 antagonists have minimal effect)
        • recent anaphylaxis (<6weeks deplete mast cells)
      • informs on likely reaction not severity
    • RAST testing
      
      • specific to IgE
      • similar value to SPT
    • food challenge
      
      • gold standard
      • hospital vs home
      • useful for review of allergies

Question 4

What is the treatment for an anaphylactic reaction?

Answer 4

• DRS ABCDE
• adrenaline 0.01mg/kg (max 0.5mg) in anterior thigh, can be repeated every 5 mins till response
• A: airway (nebulised adrenaline, early intubation)
• B: high flow O2
• C: posture - prevent collapse - supine or 45 degrees with elevated legs, get IV access and give fluid bolus
• Other treatments:
  
  • antihitamines (pruritis)
  • corticosteroids/salbutamol (bronchospasm)

LT

• Avoidance
• Medical treatment
  
  • antihistamines
  • EpiPen
• Immunotherapy
  
  • increased risk if asthma or previous anaphylaxis or β-blockers

Question 5

Outline some different types of food allergies.

Answer 5

• IgE Mediated:
  
  • generalised/anaphylaxis
  • IgE induced mast cell degranulation
  • usually rapid
  • RAST/skin prick
• Non-IgE mediated:
  
  • mainly GI:
    
    • food protein induced enterocolitis
    • food protein induced enteropathy
    • food protein induced proctocolitis
    • eosinophilic oesophagitis
  • usually intermediate (2-24hr) or delayed (>24hr)
  • Patch testing and food challenge

Question 6

What is FPIES? What is the common cause?

Answer 6

Food Protein Induced Enterocolitis Syndrome (FPIES)

• from 1 week to months of age
• cows milk, soy milk and rice are the common causes
• Presentation:
  
  • acutely unwell
  • vomiting, abdomen distension
  • bloody diarrhoea +/- CVS collapse

Question 7

FPIES vs FPIE vs FPIP - what are they and how does the prestation differ

Answer 7

• FPIES - food protein induced enterocolitis syndrome
  
  • acutely unwell
  • bloodly diarhoea
  • meningococcal-like.
  • recovers quickly once third spacing is corrected with fluid resus.
  • cows milk, soy milk, rice, corn, chicken
• FPIE - food protein induced enteropathy
  
  • unwell baby
  • vomiting and diarrhoea
  • FTT and oedema
• FPIP - food protein induced proctocolitis
  
  • cow soy or BF
  • early infancy
  • well baby with blood streaks in stool.

Question 8

What is Eosiophilic Oesophagitis? What causes it?

Answer 8

• food triggers allergic inflammatory disorder
• consider in patients who complaing of dysphagia, more common in males.
• allergic reaction to food based proteins in the diet
• Presentation:Treatment
  
  • Infants:
    
    • regurgitation
    • difficulty feeding
    • FTT
  • Adolescents:
    
    • difficulty swallowing
    • slow eaters
    • food impaction
  • Others:
    
    • epigastric pain
    • dyspepsia
    • heartburn
• Diagnosis:
  
  • histological findings
  • >15 eosinophils on biopsy with symptoms of dysfunction
  • eosinophilia after PPI
• Treatment:
  
  • food avoidance
  • may use steroids to decrease inflammation (swallowed aerolised)

Question 9

Guidelines for Epipen Prescription

Answer 9

• previous clinical diagnosis of anaphylaxis
• mod/severe food allergy with asthma
• mast cell disorder

Question 10

What is a cow’s milk protein allergy? What are the symptoms? How should you treat it?

Answer 10

• non-IgE mediated allergy
• symptoms:
  
  • diarrhoea
  • vomiting
  • rashes
  • FHx of atopy
• Treatment:
  
  • breastfeeding - keep it but eliminate cow’s milk from mother’s diet. 72 hours symptoms will improve
  • some will tolerate soy.
  • Switch to formular (hydrolyzed)
  • most rechallenge at 1 year and they grow out of it.

Question 11

What adivce can you give to parents whose child has just had an allergic reaction?

Answer 11

• educate and reassure
  
  • do not do a food challenge at home
  • go through the natural history:
    
    • reexposure can get worse
    • most resolve (30-40% in 1-3yrs, >85% 5 years, 20% in nuts/fish/shellfish)
• written anaphylaxis action plan
  
  • mild-mod - avoid causative agents
  • severe - referral, give epipen