Flashcards in Allergy and allergic disease Deck (57)
What are the different types of type 1 allergies?
- hay fever, allergic asthma, atopic dermatitis
the way a person reacts can be very different
mediated by IgE antibodies
What is the prevalence of allergies and how did they impact people's lives?
- performance - work, exams, school
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
What are the key characteristics of type 1 allergies and their Tx?
- immediate - within minutes of exposure - rapid mast cell degranulation
Tx- avoidance, antihistamine, adrenaline, steroids
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
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
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
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
What are some examples of how mild and severe allergic diseases vary?
- hay fever - mild intermittent nose itching
- eczema - mild itching of skin
- asthma - intermittent wheeze
- food allergy - mild oral itching
- persistent nasal blockage, asthma periorbital swelling
- fatal bronchospasm
- fatal anaphylaxis
What is hay fever?
- allergic response to aeroallergens (pollen, dust mites)
- effects barrier areas: - resp tract and eyes (mucosal surfaces)
- rhinorea = watery eyes
- affects 20% pop
What are the nasal and eye symptoms of hay fever?
Nasal - itching, rhinorrhoea, sneezing
eyes- allergic conjunctivitis, tears, itching, redness
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
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
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
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
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
How is mild intermittent rhinitis treated?
nasal or oral antihistamine = nasal sprays need to taken properly, head all the way forward to be effective
How is mild-moderate intermittent or persistent rhinitis treated?
nasal steroids and nasal or oral antihistamine
pre-medicate before season (if appropriate)
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
What are some of the potential reasons for treatment failure?
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
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
reversible bronchial hyper-reactivity due to smooth muscle contraction
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
What are the treatment approaches for asthma?
stabilise mast cells - sodium chromoglycate = more useful in children
treat the inflammation = steroids, LTRA (montelukast)
relieve bronchospasm - beta2 agonists
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
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
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
What does being atopic mean?
allergic to one allergen then more likely to be allergic to another allergen
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
- temporal relationship
- consistent relationship = every time they eat that food
- mouth itching/swelling/hives/angiodema
- can come at any age
What do we know about food intolerances?
pathogenesis is not fully understood
often a threshold and can tolerate varying amounts of food
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