Allergy Diagnosis and Treatment Flashcards
(89 cards)
1
Q
What is allergy?
A
An inappropriate or harmful immune response to foreign substances that are otherwise not harmful to the body, mediated largely (though not exclusively) by IgE
2
Q
What are allergens?
A
Generally proteins that elicit an IgE response in allergic individuals
3
Q
Give some examples of allergens
A
Allergic rhinitis and asthma: grass pollens, dust mite proteins, animal proteins (e.g. cat dander), moulds
Food allergy: peanuts, tree-nuts, eggs, milk, fish, crustaceans
4
Q
How is a “clinical allergy” defined?
A
Symptoms + demonstration of specific IgE response (either by skin test or RAST)
5
Q
RAST
A
Radioallergosorbent test
6
Q
What are the symptoms of allergy?
A
Dependent on route of exposure
Inhaled: rhinitis, asthma
Skin: acute contact urticaria
Mouth: oral allergy syndrome (local swelling only), cramping/vomiting/diarrhoea, can lead to anaphylaxis
7
Q
When do allergic symptoms come on?
A
Classically immediately related to allergen exposure (within 1 hour, usually secs/mins)
8
Q
What patient demographic is more likely to have an atypical allergy presentation?
A
Young children
Elderly
9
Q
List 3 types of diagnostic tests for allergy
A
Skin prick tests (SPTs)
Serologic assays (RAST, EAST, CAP-FEIA)
Challenge testing
10
Q
What is the criteria for a positive SPT?
A
≥3mm wheal
11
Q
List 3 advantages of the SPT
A
Highly sensitive (usually >99%)
In vivo exposure to allergen
Convenient and results obtained within 20 mins
12
Q
List 3 disadvantages of SPT
A
Potential (small) for anaphylaxis (mainly with SPT for latex, penicillin, venom)
May lack specificity either because of sensitised but asymptomatic individuals or through irritant false positive reactions (seen particularly with foods)
Usually require specialist clinic
13
Q
What do serologic assays measure?
A
Allergen-specific IgE
14
Q
What is RAST?
A
Radio-allergosorbent test
Now redundant but commonly used nomenclature for other serologic tests (i.e. CAP-FEIA, EAST, ELISA)
15
Q
CAP-FEIA
A
Fluro-enzymatic immunoassay
16
Q
EAST
A
Enzyme allergosorbent test
17
Q
ELISA
A
Enzyme-linked immunosorbent assay
18
Q
Describe the principles of in vitro IgE assays
A
Allergen and serum added to dish, allergen specific IgE will bind allergen
Wash out, only bound IgE remains (or only bound anti-human IgE fluoresces)
Fluorochrome-labelled mouse anti-human IgE added, binds the allergen-specific IgE
Light detector used to get a quantitative readout
19
Q
List 4 advantages of in vitro assays
A
Availability (GPs can do)
Safety
Specific particularly at a high level (class II or above; around 80-90% specific)
Standardised
20
Q
List 3 disadvantages of in vitro assays
A
Interpretation dependent on pre-test probability (FP rate usually 5-10%)
May get FPs with elevated total IgE (e.g. eczema)
Medicare only subsidises 4 tests at a time
21
Q
What is the gold standard for allergy diagnosis?
A
Challenge tests
22
Q
Where are challenge tests usually performed?
A
Only in specialised allergy clinics
23
Q
When are challenge tests usually performed?
A
Potentially risky, so usually used when RAST and SPT are negative or discordant, but there is a good clinical story
24
Q
What % of Australian children report wheeze?
A
~20%
25
Describe the role of genetics and environment in the rise of childhood food allergy
Genetic factors, FHx of atopy, parental age and maternal exposure (e.g. to Abx, probiotics, vitamin supplements, smoking, diet and food allergens) and fetal epigenetic modification all contribute to food allergy "programming" pre- and perinatally
Environmental factors including initiation of breast-feeding, exposure to sunlight (vit D) and exposure to pollutants, as well as infant dietary factors and factors associated with the "hygiene hypothesis" contribute to onset of food allergy postnatally
26
Describe 5 factors associated with the "hygiene hypothesis"
Increased sanitation, immunisation, Abx use
Decreased infections
Exposure to farm animals, domestic pets and endotoxins
Decreased microbial load in food and water
Presence of siblings
27
What symptoms are seen in an acute vs chronic allergic reaction? What mediates these responses?
Acute (related to mast cell activation): wheeze, urticaria, sneezing, rhinorrhoea, conjunctivitis
Chronic (related to mast cell activation, neuropeptide release from TH2 cells and eosinophils): further wheeze, sustained blockage of the nose, eczema
28
List 2 allergen-specific treatments for allergy
Allergen avoidance
| Allergen specific immunotherapy
29
List 5 non-specific medical therapies for allergy
```
Antihistamines
Corticosteroids
Adrenaline
Leukotriene antagonists
Anti-IgE Abs (e.g. omalizumab)
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30
Describe the typical course of subcutaneous allergen immunotherapy
Increasing doses of allergen extract given subcutaneously initially weekly and then monthly for 3-5 years
31
What allergy therapy is the only one to provide prolonged improvement or cure?
Immunotherapy
32
What is the major risk in injection immunotherapy?
Small but important risk of anaphylaxis with SC immunotherapy (reported death rate from US data 1 in 2,000,000 injections)
33
Who should provide injection immunotherapy?
Generally recommended to be initiated and/or supervised by an allergy specialist
34
What is the main indication for SC injection immunotherapy?
```
Venom allergy (e.g. bee, European wasp)
Allergic rhinitis +/- mild, well controlled allergic asthma (stable symptoms and FEV1 >70% predicted)
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35
Why must allergic asthma be mild and well controlled for injection immunotherapy to be considered as a treatment option?
Level 1 evidence that it works in allergic rhinitis and allergic asthma, but risk of adverse reactions is higher in asthmatics (must have STABLE symptoms and FEV1 >70% predicted)
36
Name one contraindication to allergy immunotherapy
Co-existent B blockade
37
Describe the proposed mechanism of allergy immunotherapy
Allergen presented by APC to Th0
Th0 releases IL-4, stimulates Th2 to release IL-4 and IL-5 which results in the production of IgE by activated B cells (the ALLERGIC response)
Following immunotherapy, Th0 releases IL-12 when stimulated by APCs; IL-12 induces release of IFN-y from Th1 cells, which acts on B cells to stimulate production of IgG (the NON-ALLERGIC response)
38
Describe some practical aspects of injection allergen immunotherapy
Always wait at least 30 mins in surgery after injection
Usually antihistamine prior is advisable
Always check the dose and extract
Adrenaline and O2 must be available for treatment of anaphylaxis if it occurs
39
Which is more effective: sublingual or subcutaneous immunotherapy?
Appear to be equally effective
40
What are the advantages of sublingual immunotherapy?
Minimal risk of anaphylaxis (no deaths reported with use)
| Can be administered at home by patient
41
What is the limitation of sublingual immunotherapy?
Extracts are more expensive
42
Describe the method of sublingual immunotherapy
Dose of allergen extract self-administered daily by patient sublingually, held for 2 mins under the tongue and then swallowed
43
Define anaphylaxis
No clear consensus on definition; "serious allergic reaction that may cause death"
Generally implies IgE-mediated (as opposed to anaphylactoid which is non-IgE mediated)
Is a generalised serious IgE-mediated allergic reaction which usually involves CV (hypotension) and/or respiratory tract (asthma/laryngeal oedema)
Atypical presentations (e.g. without rash) are not uncommon, particularly in the very old or very young
44
Describe the proposed mechanism of anaphylaxis
Massive mediator release primarily from mast cells and circulating basophils
Vasodilation, fluid extravasation, bronchial smooth muscle contraction and mucosal oedema
Death due to shock and/or hypoxaemia
45
Describe some "mild" anaphylactic symptoms
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Pruritis (particularly in hand and groin)
Urticaria
Flushing
Vomiting
Diarrhoea
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46
Describe some moderate and severe anaphylactic symptoms
Angioedema (particularly of lips, tongue and larynx)
Wheeze, asthma
Hypotension
LOC
47
Describe the death rate from anaphylaxis
One death per 3 million population per annum
48
What are the main causes of fatal anaphylaxis?
Food allergy (especially nuts)
Insect venom
Drugs
49
What is the risk of death per nut allergic person per year?
2.3/100,000 risk of death per nut allergic person per year
50
What medications are most commonly associated with fatal anaphylaxis?
Anaesthetics
Abx
Contrast
51
What foods are commonly associated with allergy?
```
Peanuts
Tree-nuts
Eggs
Milk
Fish
Crustaceans
```
52
Does anaphylaxis ever remit?
Anaphylaxis is often life-long, except for egg and milk allergy which frequently remit (cf peanut, only ~30% of children remit)
53
How is food allergy causing anaphylaxis managed?
Avoidance
| Mx of inadvertent exposure (adrenaline)
54
List 5 risk factors for fatal food-related anaphylaxis
```
Associated asthma
Lack of self-injectable adrenaline (Epipen, Anapen)
Young adults
Alcohol
Extreme sensitivity
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55
List the 3 main insect venom allergies
Bee
European wasp
Jumper ants
56
How do bee deposit their venom? How much venom is deposited per sting?
Via a barbed modified ovipositor which is left in the skin (sting only once)
Each sting deposits 35-200 mcg of venom
57
How do European wasps deposit their venom? How much venom is deposited per sting? When are stings most commonly acquired?
Can sting multiple times
10-20 mcg of venom per sting
Nests in concealed locations (underground, logs, wall cavities); single queen starts a new colony each spring, and wasps become most aggressive towards the end of summer
58
Where are jumper ants most prevalent? How can jumper ant venom allergy be treated?
Unique to Australia; prevalent in Tas, Northern suburbs of Melbourne and Bellarine Peninsula
Immunotherapy effective but availability currently limited in Victora
59
What is the efficacy of immunotherapy for insect venom allergy?
Efficacy 95% with vespid, 75-80% with bee venom
60
What protocols are available for immunotherapy for insect venom allergy?
Standard
Cluster "rush"
"Ultrarush"
61
How long should immunotherapy protocols last for insect venom allergy?
5 years
62
What precautions should be taken with immunotherapy for insect venom allergy?
Epipen should be available until negative sting reaction is achieved
63
Mr SM, 38 year old postie, stung at work by a bee (confirmed as left a stinger - no other insects do)
Experienced generalised urticaria, breathlessness
Ambulance called
Administered IM adrenaline 0.5mg, hydrocortisone and phenergan en route to ED
Dx?
Ix?
Mx?
Dx: honeybee venom allergy
Ix: RAST (was strongly positive, Class 3 out of 4, to honeybee)
Mx: desensitisation to honey bee recommended and Epipen and anaphylaxis plan provided
64
In what populations is latex allergy typically seen?
Healthcare workers
| Spina bifida patients
65
What symptoms are commonly seen in latex allergy?
Irritant or contact dermatitis
| Can be associated with urticaria, rhinitis, asthma and even anaphylaxis
66
Why is latex allergy less of a problem now?
Has decreased in importance due to reduction in protein content of latex gloves
67
What other things are cross reactive with latex allergens?
Banana
Avocado
Kiwi fruit
68
What Abx are the main causes of allergy?
Penicillins
| Cephalosporins
69
What is the mechanism of allergy to radiocontrast agents?
Anaphylactoid (non-IgE mediated)
70
What anaesthetic agents are more strongly associated with allergy?
Muscle relaxants
71
What medication is a common cause of serious anaphylaxis but is often not thought of as a "medicine" but patients?
NSAIDs
72
Give an example of a natural medicine which is associated with allergy
Echinacea
73
How is anaphylaxis diagnosed?
Clinical diagnosis; broad differential including CV and other disorders
RAST testing, skin prick testing (when safe) and measurement of mast cell tryptase may aid diagnosis
74
What is mast cell tryptase and how is it associated with anaphylaxis?
An enzyme released during degranulation of mast cells
| Peaks around 4-6 hours post-anaphylaxis
75
Describe the current Australian guidelines for emergency management of anaphylaxis
Stop administration of causative agent (if relevant), assess reaction severity and treat accordingly: call for assistance, give adrenaline IM (lateral thigh, 0.1 mg/kg to max dose of 0.5 mg), set up IV access, lay patient flat (elevate legs if tolerated), give high flow O2 + airway/ventilation support if needed, if hypotensive also set up additional wide-bore IV access and give IV normal saline bolus 20 mL/kg over 1-2 min under pressure
If there is inadequate response, an immediate life-threatening situation, or deterioration: start an IV adrenaline infusion OR repeat IM adrenaline injection every 3-5 min, as needed
76
Describe the principles of long-term allergy therapy
Avoidance
Education on action plan: recognise symptoms, when to seek help, adrenaline injection, antihistamine tablets, desensitisation if relevant
Medical alert bracelet
"Action plan" for anaphylaxis
77
Describe the typical appearance of urticaria
Circumscribed, slightly elevated, intensely pruritic skin lesions
Initially erythematous but can develop central pallor as oedema develops in the dermis
Can occur anywhere including face and scalp
Individual lesions rarely last longer than 24 hours
No residual skin staining
78
Describe the typical appearance and presentation of urticaria
Non-pruritic, less erythematous and less clearly defined swelling occurring in the deep dermis or subcutaneous tissues
Can occur anywhere under skin or mucous membranes but frequently involves face including eyelids, lips or tongue
Often associated with a burning sensation or pain
Can last for up to 3 days
79
What is chronic urticaria and angioedema indicative of? How can it be distinguished from acute allergy-related urticaria and angioedema?
Commonly not due to allergy
| Clue is in the Hx: recurring lesions with no obvious temporally related allergic trigger
80
How is chronic urticaria and angioedema managed?
Antihistamines are mainstay of treatment
81
In the case of chronic urticaria and angioedema, what other diagnoses must be excluded?
AI disease (e.g. SLE) and other rare diseases (e.g. hereditary angioedema) may need to be excluded (amongst other Ix) if symptoms are severe or persistent
82
What allergens are typically associated with allergic rhinitis?
```
Perennial (year round allergens) include dust mite, pets (principally cats) and moulds
Seasonal rhinitis (springtime hayfever) usually due to grass pollen
```
83
How is allergic rhinitis managed?
Nasal corticosteroids and/or antihistamines
| Allergen specific immunotherapy is useful if medical therapy is inadequate/not tolerated (level 1 evidence)
84
Master AK, 10 year old boy
PHx: eczema since 6/12 old, asthma since 6 years old, rhinorrhoea and nasal obstruction since 8 years old
Eczema and rhinitis have worsened recently
Mother is concerned regarding food allergies
Further Qs?
More detail regarding Hx and severity of atopic disorders, particularly regarding severity and possible hospitalisation for asthma
Previous treatments and efficacy
Qs regarding allergen exposure (e.g. dust, moulds, pets, seasonal variation, foods)
FHx
85
Master AK, 10 year old boy
PHx: eczema since 6/12 old, asthma since 6 years old, rhinorrhoea and nasal obstruction since 8 years old
Eczema and rhinitis have worsened recently
Mother is concerned regarding food allergies
O/E: widespread chronic eczema esp face, cheeks and eyelids, flexural areas of arms and legs and hands, swollen pale boggy nasal turbinates with reduced nasal airflow bilaterally (polyps not present), clear chest examination
Mx?
Allergen avoidance: no efficacy demonstrated for primary prevention, greater evidence for allergen avoidance in ESTABLISHED allergic disease
Allergy Dx can direct avoidance of SPECIFIC allergens only (e.g. animals, occupational, etc)
I.e. does not need to avoid potential food allergens unless there is a proven Hx of food allergy
86
Mr UD, 61 year old cotton goods importer and non-smoker, developed severe SOB during springtime thunderstorm
PHx: asthma since childhood, springtime hayfever
Required intubation in ED for acute respiratory failure and transferred to ICU for mechanical ventilation
Commenced budesonide/eformoterol (Symbicort) inhaler and oral prednisolone
Extubated, mobilised, discharged after 1 week
At follow up he feels well and is on inhaled corticosteroids (Symbicort), intranasal steroids (Nasonex) but his lung function still shows severe airflow obstruction (FEV1 30%)
Dx?
Ix?
Mx?
Dx: acute exacerbation of asthma due to springtime allergy
Ix: RAST (results were strongly positive for grass pollen)
Mx: immunotherapy not appropriate as he has severe asthma and FEV1
87
What is a negative RAST result?
Less than 0.35kU/L of specific IgE
88
Describe the proposed mechanism of thunderstorm asthma
Whole pollen grains get swept up into cloud as storm matures
Moisture in the cloud fragments the pollen into smaller pieces
Dry, cold outflows carry pollen fragments to ground level, where people breathe them into their lungs
89
What is the mainstay of acute anaphylaxis Mx?
IM adrenaline
