Allergy Flashcards
(31 cards)
What is allergy?
Allergy is an objective, reproducible reaction mediated via the body’s immune system, initiated by exposure to a defined stimulus at a dose tolerated by normal persons.
What is the difference between food allergy and food intolerance?
Food allergy is immune mediated but a food intolerance is NOT immune mediated
Simply, what are the 3 categories of food allergy in terms of the immunoglobulin involved?
IgE mediated – immediate, symptoms appear minutes to 2 hours after ingestion
Mixed IgE and NON-IgE mediated
Non-IgE mediated – 4 hours to days (T-cell mediated)
What is meant by food intolerance and what are the 3 categories of intolerance? Give an example of each.
Food intolerance is a reaction initiated by non-immunological mechanisms. The 3 categories are metabolic, pharmacologic and toxic.
Metabolic – CHO malabsorption (lactose intolerance)
Pharmacologic – Caffiene causing irritability, restlessness and palpitations
Toxic – Food poisoning (salmonella, fish toxins)
What is meant by atopy? Does it always lead to allergic disease? What are some examples of some atopic disease?
Atopy is the genetic predisposition to be sensitised as it produces IgE antibodies in response to ordinary exposures to common environmental allergies. This can lead to allergic disease but not necessarily.
Examples of atopic disease include asthma, allergic rhino-conjunctivitis, eczema, IgE mediated food allergy
What are 3 common triggers of an allergic response? (there are 6)
Foods (nuts, shellfish etc.) Stings (wasps and bees etc.) Drugs (penicillin, NSAIDs, ACEi) Radiographic contrast media Blood Products Latex
What are 5 of the major food groups that cause >90% of food allergies? (There are 8)
Peanuts Soy Eggs Milk Fish Wheat Shellfish Tree nuts
What type of hypersensitivity reaction is anaphylaxis?
Type 1 (IgE-mediated) Hypersensitivity Reaction. It is a result of the degranulation of IgE bound mast cells releasing various mediators causing systemic consequences
Explain the pathophysiology behind the 1st exposure of a person to an allergen in an IgE mediated food allergy
On 1st exposure
Allergens are introduced to the body through various routes: ingestion, inhalation, paraenteral, skin contact. When the person is first exposed to the allergen, they make IgE antibodies specific to the allergen which attach to the high affinity Fc receptors which are found on basophils and mast cells.
Explain the pathophysiology behind the 2nd exposure of a person a specific allergen allergen in an IgE mediated food allergy
On 2nd exposure
On subsequent exposure to the allergen, it will bind to the IgE antibodies on the mast cells and the basophils -> this will cause the degranulation of these mast cells -> Histamine, prostaglandin D2, leukotrienes, platelet-activating factor, tryptase*, nitric oxide, eosinophils and neutrophil chemotactic factors will all be released as a result of the degranulation-> this will cause varying effects on target organs
Following the degranulation of the mast cells and release of mediators into the systemic circulation, what are the 6 key effects of these mediators throughout the body?
- Increased Vascular Permeability
- Vasodilation
- Myocardial Dysfunction
- Altered Smooth Muscle Tone -> bronchospasm and uterine cramps
- Activation of Sympathetic Nervous System -> tachy, increased mucus, anxiety
- Increased Platelet Activation
What is the signs and symptoms of an IgE mediated food allergy?
Onset of around 2 hours
Systems involved: Cutaneous, Gastrointestintal, Respiratory, Cardiovascular
Cutaneous: Erythema, pruritis, urticaria, angioedema
Gastrointestinal:
- Oral – Pruritis, Lip and Tongue Swelling
- Lower – Nausea, colicky abdominal pain, vomiting, diarrhoea
Respiratory:
- Upper – nasal congestion, rhinorrhoea, sneezing, hoarseness
- Lower – cough, chest tightness, dyspnoea, wheeze, accessory muscle use
Cardiovascular: tachycardia (bradycardia), hypotension, dizziness, fainting, LOC
What is urticaria?
Blanching, raised, palpable wheals which can be linear, annular or arcuate on any skin area
What is angio-oedema?
Vascular permeability is increased in anaphylaxis which causes fluid to leak from blood vessels causing swelling. Can occur in the face, lips, tongue, lips, tongue and genital area but also in the throat which can also cause shortness of breath. 50% of the intravascular fluid will move to the extravascular space in minutes.
What is anaphylaxis?
Anaphylaxis is an acute, severe, life-threatening allergic reaction in pre-sensitised individuals, leading to a systemic response caused by release of immune and inflammatory mediators from basophils and mast cells. At least 2 organ systems are involved such as skin, upper and lower airways, cardiovascular, neurological, GI systems in this order of priority or in combination.
Who are the people that are in the High Risk group for having an anaphylactic attack? (6 points)
History of Anaphylaxis Multiple food and drug allergy Poorly controlled asthma Underlying lung disease Beta-blockers/ACE inhibitors Older age
What are the 3 key points which are integral to the clinical presentation of anaphylaxis?
- Rapid Onset of Symptoms
- Compromise of one of ABC (Airways, Breathing, Circulation)
- Involvement of Skin/Mucosa
What are the 6 points which are important to elicit in a history of an allergic reaction or an anaphylactic attack?
What was ingested? (peanut butter sandwich vs mixed nuts)
Amount ingested? (nut touched lip vs whole packet of nuts)
How was it cooked? (egg within cake vs licking raw egg batter)
Timing of exposure to onset/offset
Treatment needed
Previous exposures
What are some common clinical features of a patient presenting with anaphylaxis?
Difficult/noisy breathing Swelling of the tongue Swelling/tightness in throat/Difficulty swallowing Difficulty in talking or hoarse voice Wheeze or persistent cough Persistent dizziness or collapse Pale and floppy infant/young child
What is an investigation that can be used in the diagnosis of anaphylaxis?
Anaphylaxis is a clinical diagnosis.
A raised mast cell tryptase can be a useful clue in the diagnosis of anaphylaxis. This test should only be conducted if the diagnosis is unclear and is confused with life-threatening cardiac or respiratory collapse. This serum tryptase returns to normal hours after anaphylaxis AND normal serum tryptase does not rule out anaphylaxis.
What is are the key points in the management of a patient experiencing an ANAPHYLACTIC ATTACK? **
IM ADRENALINE!!! (epipen is crucial) – into antero-lateral thigh and repeat in 5 mins if no improvement.
A: Airway Obstruction
- Nebulised Adrenaline – only used if upper airway obstruction is present
- Early intubation or laryngeal mask – if airway oedema is not responding to nebulised adrenaline
- If complete obstruction: bag mask ventilation with high flow O2
B: Breathing
- High Flow O2
C: Circulation
- Posture: prevent exacerbating collapse – keep patient supine or at 45 degrees if any breathing difficulty
- IV access with large gauge cannula – saline fluid bolus as a volume expander and may consider adrenaline infusion.
- If no pulse is detected: begin resuscitation
What are the key points in the management of a patient experiencing a GENERALISED ALLERGIC REACTION?
Anti-histamines* Cool Compress Observation Identify trigger Allergy Action Plan* Education and Referral
What are some investigations that can be made in follow-up management after the stabilisation of the patient or in the context of a relatively minor allergic reaction?
Skin Prick Test – Allergen scratched on back and wheal is measured at 15 mins. +ve. >3mm wheal is positive result. The larger the wheal the more likely an IgE mediated reaction will occur. It does NOT tell you the severity of the reaction itself. Correlation with Hx is critical.
Serum Specific IgE – detects free antigen specific IgE in serum. Results are usually concordant with the skin prick test.
Food Challenges – Gold standard for allergy diagnosis. This confirms the diagnosis of a food allergy. This can also test the tolerance/resolution of food allergy.
What are the types of non-IgE mediated food allergy conditions?
Mainly GI, skin symptoms/signs Food Protein Induced Enterocolitis Syndrome Food Protein Induced Enteropathy Food Protein Induced Proctocolitis Esosionophilic Oesophagitis
