Allergies Flashcards
Define hypersensitivity
Damage to a patient caused by the immune system
Define allergy
A type 1 hypersensitivity reaction in response to foreign antigens
What is involved in a type 1 hypersensitivity reaction?
IgE Mast Cells
What is involved in a type 2 hypersensitivity reaction?
Autoantibodies
What is involved in a type 3 hypersensitivity reaction?
Immune mediated complexes
What is involved in a type 4 hypersensitivity reaction?
T cells
What is involved in a type 5 hypersensitivity reaction?
Upregulation (eg Graves)
What is anaphylaxis, and briefly, what happens within anaphylaxis? What is released?
A type 1 hypersensitivity reaction
- Degranulation and activation of mast cells and basophils
- Release of leukotrienes and histamine
Signs and Symptoms of anaphylaxis?
Syncope Bronchospasm (wheeze) Urticaria (red, itchy rash) Angioedema (swelling with fluid in subcut tissue) Abdo pain Vomiting Diarrhoea
What test is used to diagnose anaphylaxis?
Tryptase
Differentials for anaphylaxis?
PE MI Hyperventilation Hypoglycaemia Vasovagal
Describe the short term treatment of anaphylaxis
- IM Adrenaline
- Oxygen 100%
- IV fluids
- IV glucocorticosteroids and antihistamines
What is the long term treatment of anaphylaxis?
- Identify antigen responsible
- Avoid antigen
- Can use prophylactic antihistamine
- Carry adrenaline injection device
- Sometimes, densensitisation
Define anaphylactoid reaction?
The direct or indirect activation of mast cells without IgE
What are some causes of anaphylactoid reactions
a) drugs
b) food
c) physical stimuli
a) Vancomycin, opiates, NSAIDS
b) Strawberries
c) exercise, cold, truama
Are anaphylactoid reactions tryptase positive
Yes
Define scromboid
Massive ingestion of histamine from decayed mackrel and other oily fish.
Are scromboid reactions tryptase positive?
No, as mast cells not involved
What is urticaria?
Raised, itchy, erythermous rash
Inflammation within the dermis
Name allergic causes of urticaria?
Usually acute or chronic?
- Anaphylaxis, anaphylacoid and scromboid (drugs, food and arthropod venoms)
- Local injections of antigens such as bites and scratches
- Direct contact: latex gloves, grass
Usually acute
Describe the autoimmune causes of urticaria
Autoantibodies to Fc- Epsilon receptors on mast cells/ basophils SLE Vasculitis Injected serum/ blood products Type 3 hypersensitivity (usually)
What infections can cause urticaria
Hep B
H. Pylori
Lymes Disease
What deficiencies can cause urticaria
B12
Folate
Name a mast cell disorder that cause cause urticaria
Urticaria pigmentosa
When in the menstrual cycle have urticaria been reported?
Luteal phase- progesterone
What are the following associated with
a) cholinergic urticaria
b) adrenergic urticaria
a) heat and sweating
b) stress
What 3 drug classes are recommended in the treatment of acute urticaria
1) Antihistamines
2) Rantidine (H2 antagonist)
3) Montelukast (leukotriene antagonist)
Which antihistamine is older and more sedative
Chlorphenamine