Case 14: Allergy Flashcards
1
Q
Atopy
A
- An exaggerated propensity in genetically predisposed individuals to produce IgE and Non IgE responses to common environmental triggers.
- The IgE mediated Allergic March: allergic comorbidities evolve through time in a pre-set pattern. When a patient present with one comorbidity ask about the others
- Types of allergic co-morbidities: Atopic dermatitis (Eczema), food allergy, Allergic Rhinnitis (hay-fever), Atopic asthma, Drug allergy
2
Q
Allergy history
A
- Timing: did it start during weaning
- Nature of reaction: sudden or delayed
- Reproducibility: occur everytime they are exposed to the allergen
- How much allergen does it take to produce the reaction
- Was the allergen tolerated before or not
- Whether sensitised, allergic or tolerated they will have the same blood results so need history to distinguish them
3
Q
Skin allergy: IgE mediated and non-IgE mediated
A
- Both: Pruritus, Erythema
- IgE mediated: acute Urticaria (wheel shaped) localised or generalised. Acute angioedema- of the lips, face and around the eyes
- Non IgE mediated: Atopic suppurative eczema, Multi-system organ disease
4
Q
Atopic dermatitis (eczema)
A
- due to genetic mutation (filaggrin mutation) causes increased sensitisation across leaky skin.
- Children are at higher risk of IgE and non- IgE food allergy.
- Can lead to Eczema Herpeticum and S.aureus/Streptococcus infections
- Discoid eczema: not related to food allergy
5
Q
GI allergy symptoms: IgE and non IgE mediated
A
- Both: Faltering growth due to malnutrition- any child with eczema and faltering growth should be referred to a dietician
- IgE mediated: Angiodema of the lips, tongue and palate, Oral pruritus, nausea, colicky abdo pain, vomiting, diarrhoea. Consider anaphylaxis if skin symptoms with acute abdo pain, vomiting, marked diarrhoea with collapse
- Non-IgE mediated: Delayed symptoms due to inflammation of gut wall and dysmotility. GORD, loose or frequent stool, blood and or mucus in stool, abdo pain, infantile colic, food refusal or aversion, constipation, perianal redness, pallor or tiredness
6
Q
Most common food allergies
A
- Children: cows milk, eggs, nuts
- Adults: fish, shellfish, kiwi
- Non-IgE mediated: soya, wheat, cows milk
7
Q
Management: food allergies
A
- Food allergy management plan: state the trigger and outline how to treat mild, moderate and severe symptoms
- Anyone with asthma and moderate food allergy should have an adrenaline autoinjector
- Prescribe a ‘Rescue Medication Pack’: Antihistamine (i.e. cetirizine), Bronchodilator (i.e. Slabutamol), Adrenaline autoinjectors
8
Q
Investigations of non IgE mediated allergy
A
- eosinophils, basophils, mast cells
- gut biopsies
- nutrition growth centiles
9
Q
Allergy investigations
A
- Two main options: Skin prick testing, Specific IgE testing
- Neither confirms allergy just by positive result- instead shows sensitisation (patient produces specific IgE against the allergen) but that can be asymptomatic
- Also: Intradermal testing and Challenges
- Need history
10
Q
Skin Prick Testing (SPT)
A
- Can be done for most IgE mediated allergies: foods, inhalants (dust/pollen), bee/wasp venom, some drugs
- Normally uses liquid reagents (allergen extracts) can be done with native allergens as prick-prick test (fresh food, drugs)
- Wait 15 minutes after administration to see results. Positive is a red wheel surrounded by white flare
- Positive (histamine) and negative (saline) controls are essential to ensure valid test (rule out suppression with e.g. antihistamines, and false positive due to pressure / dermographism)
11
Q
Skin prick testing (SPT’s): pros and cons
A
- Pro’s: rapid result (15 min), wide range of allergens, cheap, good specificity and less prone to false positives then blood tests in atopic patients
- Cons: Exposure to allergen so (low) risk, difficult if severe skin pathology (active eczema), cant be on antihistamine/some other drugs (antidepressants and antipsychotics), labour intensive
12
Q
Specific IgE testing
A
- Blood test using enzyme immunoassay on the ImmunoCap platform
- Gives a quantitative result in kAU/L. Negative <0.35
- Pros: Zero allergen exposure (no anaphylaxis), not affected by other drugs, wide range (not unlimited) of allergens, can test individual components as well as whole substances
- Cons: False positives, especially in atopy (raised total IgE), expensive, some allergens not available, variable sensitivity (very low for drugs)
13
Q
Intradermal testing (IDT)
A
- Almost exclusively used for drug allergy testing
- Higher sensitivity than SPTs, but also higher risk
- Conducted with diluted drug in liquid form where its injected in-between the skin layers causing a bleb to form. If positive will form wheel with flair
- Cons: more likely to cause reactions
- Start with SPTs first, and IDTs if negative
- Only used for a small number of drugs (mostly antibiotics)
14
Q
Food and drug challenge (AKA Provocation test)
A
- Gold standard for ruling out allergies
- Not needed if considered low risk after standard testing (skin prick and bloods)- can go straight to home reintroduction
- Patient given drug or food in controlled dose and under observation
- Graduated or single dose (depending on risk)
- Treatment for allergic reactions immediately available
- Differentiating non-allergy (e.g. anxiety-mediated) and allergic symptoms can be difficult
- Occasionally done as double-blinded, placebo controlled challenge (multiple appointments – very labour intensive)
15
Q
Patch testing
A
- Test for contact dermatitis (type IV hypersensitivity)
- Patches applied to skin and left for 48-72 hours: positive would be erythema
- Use chemicals found in cosmetics, hair dyes, dental procedures etc.
- Conducted by Dermatology
- NOT useful for investigation of IgE-mediated allergy
16
Q
Component resolved diagnostics
A
- Testing different allergen components separately rather than all together
- allows identification of true allergy (certain allergen components are more likely to be markers of true allergy)
- allows risk stratification (certain allergen components are more associated with severe reactions)
17
Q
Anaphylaxis features
A
- sudden onset and rapid progression ofsymptoms
- Airway and/or Breathing and/orCirculation problems (one must be present)
- skin and/or mucosal changes (flushing, urticaria, angioedema)- can be absent
- Diagnosis is supported if patient has been exposed to an allergen known to affect them
18
Q
Anaphylaxis timing
A
- Quicker presentation with IV drugs and stings, slower for food or oral medication. Symptoms present within first few minutes to an hour after exposure
- Food- 30mins
- Sting- 12mins
- Drugs- 1min
19
Q
Anaphylaxis: symptom progression
A
- Mild, localised skin symptoms and/or swelling of the lips/face. Rhinitis or Conjunctivitis
- Generalised skin reaction
- Airway/Breathing/Circulation problems +/- skin problems (80% have skin problems)
20
Q
Anaphylaxis: ABCDE
A
- Airway: hoarse voice, stridor
- Breathing: increased work of breathing, wheeze, fatigue, cyanosis, SpO2 <94%
- Circulation: hypotension, signs of shock, confusion, reduced consciousness
- Disability: dizziness, decreased conscious level or loss of consciousness
- Exposure: flushed, itchy, urticaria or hives, angiodema
