Allergy and allergic disease Flashcards Preview

Yr 3 - December lectures 2018 > Allergy and allergic disease > Flashcards

Flashcards in Allergy and allergic disease Deck (57)
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1

What are the different types of type 1 allergies?

aeroallergy
- hay fever, allergic asthma, atopic dermatitis
food allergy
drug allergy
venom allergy
the way a person reacts can be very different

mediated by IgE antibodies

2

What is the prevalence of allergies and how did they impact people's lives?

1:3
- QoL
- concentration
- performance - work, exams, school
- socialisation
- diet
- sleeping/snoring
- anxiety

3

Why has there been an increase in allergy?

no single factor explains the rise - combo of genetic and environmental
Hygiene hypothesis - all too clean now => lack of exposure to germs, skews Th1 cell response to a Th2 cell response

4

What are the key characteristics of type 1 allergies and their Tx?

IgE mediated
- immediate - within minutes of exposure - rapid mast cell degranulation
- life-threatening

Tx- avoidance, antihistamine, adrenaline, steroids

5

What are the key characteristics of type 4 allergies and their Tx?

T cell mediated
> 4 hours, often a day or 2 after antigen exposure
Tx = avoidance, steroids
much less severe than type 1

6

What is the process of developing a type 1 allergy?

1) allergen exposure
2) sensitization => can't have a reaction on 1st exposure
3) specific IgE production
4) Re-exposre to allergen = acute allergic response
5) Long-term exposure leads to chronic inflammation or tolerance e.g. chronic asthmas - scarring and remodeling - can desensitize by giving them a higher dose than normal exposure in environment

7

What are the molecules involved in type 1 allergy and what happens?

antigen activates IgE (antibody class that can stimulate allergy cells)
- high affinity receptor on mass cell that cross link the antigen and IgE
- allergy cell that releases substances that cause allergic symptoms

8

What are the mast cell mediators and what do they cause?

histamine, prostaglandin, leukotrienes, PAF, tryptase
- vasodilation (erythema)
- vascular permeability (swelling)
- heart rate, cardiac contraction - hypotension
- glandular secretion - IL13 release
- bronchoconstriction

9

What are some examples of how mild and severe allergic diseases vary?

Mild
- hay fever - mild intermittent nose itching
- eczema - mild itching of skin
- asthma - intermittent wheeze
- food allergy - mild oral itching

Severe
- persistent nasal blockage, asthma periorbital swelling
- fatal bronchospasm
- fatal anaphylaxis

10

What is hay fever?

allergic rhinitis
- allergic response to aeroallergens (pollen, dust mites)
- effects barrier areas: - resp tract and eyes (mucosal surfaces)
- rhinorea = watery eyes
- affects 20% pop

11

What are the nasal and eye symptoms of hay fever?

Nasal - itching, rhinorrhoea, sneezing
eyes- allergic conjunctivitis, tears, itching, redness

12

Why is it important to discuss when pts get hay fever?

it can help to identify what causes their hay fever
- e.g. tree pollen tends to be high in spring, grass pollen tends to be higher in early/mid summer, fungal spores tend to higher mid/late summer

13

What tests are available to support history?

serum specific IgE - helpful to back up history but sensitivity and specificity only 60-80%, false positives (atopic dermatitis)
total IgE - guide, helps interpret ssIgE
Skin prick tests = more sensitive than ssIgE

14

What happens in skin prick tests and what do they rely on?

relies on IgE mediated local reaction
- gives immediate answer
itchy, doesn't really hurt
results within 20 mins

15

What are some examples of unproven allergy tests and what are the problems with them?

hair analysis, pulse test, cytotoxic food testing, ELISA/ACT
- a lot of these are actually for intolerances and therefore are not that helpful

16

How easy is it avoid allergens?

animal dander is straightforward= don't have pets
grass, dust mites, moulds are much more difficult
therefore if you can't avoid them you need to treat them

17

How is mild intermittent rhinitis treated?

allergen avoidance
douching
nasal or oral antihistamine = nasal sprays need to taken properly, head all the way forward to be effective

18

How is mild-moderate intermittent or persistent rhinitis treated?

regular treatment
nasal steroids and nasal or oral antihistamine
pre-medicate before season (if appropriate)

19

What additional therapies can be added on if you are still suffering from rhinitis?

ipratropium, increase antihistamine dose, short term course of oral steroids, immunotherapy

20

What are some of the potential reasons for treatment failure?

compliance
not taking the treatment properly
not taking it due to side effects
try different device
pre-season medication may be necessary = generally more effective if you stop inflammation happening in the first place

21

What happens in allergic asthma?

one of the phenotypes of asthma
symptoms worse on exposure to allergen but also complex late phase responses due to inflammation
direct bronchospasm
reversible bronchial hyper-reactivity due to smooth muscle contraction

22

How are rhinitis and asthma linked?

concept of one airway
- 80% of asthmatics have rhinitis
- 20-50% of patients with rhinitis have asthma
allergic rhinitis is an important independent risk factor for asthma

23

What are the treatment approaches for asthma?

avoid triggers
stabilise mast cells - sodium chromoglycate = more useful in children
treat the inflammation = steroids, LTRA (montelukast)
relieve bronchospasm - beta2 agonists

24

What is atopic dermitits/eczema and what are some risks associated with it?

allergic skin disease and immunodeficiency and chronic inflammation
more complex response to allergen than hay fever or asthma
very high IgE but allergen is not usually identified
T cells and infection with S aureus important = if barrier is broken more likely to come into contact with immune cells
often underlying genetic defect in barrier defense

25

What genetic defect is thought to be involved in asthma?

filaggrin - structural protein in the keratinocyte layer - only discovered about 10 years ago
70% of atopic dermatitis

26

What are the treatments for eczema?

avoid the allergen and prevent scratching
prevent barrier defense breakdown (moisturizers deluxe)
- the key treatment is moisturisation
treat the infection - antibiotic creams
treat the chronic inflammation = steroids

27

What does being atopic mean?

allergic to one allergen then more likely to be allergic to another allergen

28

What is a key factor in food allergies and what is important to ask in the history?

patients usually tell you what the food is
take food allergies seriously as they can be life-threatening
Hx
- temporal relationship
- consistent relationship = every time they eat that food
- mouth itching/swelling/hives/angiodema
- can come at any age

29

What do we know about food intolerances?

pathogenesis is not fully understood
Non-IgE mediated
often a threshold and can tolerate varying amounts of food
unpredictable
non-life threatening but distressing
abdominal discomfort, bloating, vomiting, nausea, diarrhea, headache, feeling unwell
no reliable diagnostic tests except avoidance reintroduction diets
can be difficult to distinguish from IBS

30

How are food allergies managed?

avoidance
antihistamines
adrenalin
mx plan
medical alert
medical notes