Case 7- treating allergic diseases Flashcards
Long acting histamine
Provides symptom relief for 8-12 hours
Shorter acting histamines
Last up to 4 hours but begin working faster
First generation antihistamine side effects
Drowsiness, difficulty urinating, dizziness, dry mouth, blurred vision, tinnitus and constipation
First generation antihistamines
Chlorphenamine, Diphenhydramine
Second generation antihistamine side effects
Less likely to cause side effects
Examples of second generation antihistamines
Cetirizine (Active ingredient in OTC medicine Zyrtec) and Loratadine (active ingredient in OTC medicine Claritin.
Eosinophilic esophagitis
An allergic inflammation of oesophagus which involves build up of eosinophils in its lining. There is dis-mobility of the oesophagus so it cant move much, you get difficulty swallowing. It is non-IgE mediated. You are likely to have other allergies which are IgE mediated
First thing to discuss in an allergic reaction
Ask about exposure- was there a clear temporal relationship with the trigger, the consistency of the reaction does it happen every time they are exposed to the substance. Is it a typical allergen? Timing, IgE mediated allergy is within 2 hours of ingestion. Ask about atopy and family history. History identifies allergen 50% of the time
Common IgE mediated food allergies
Cow’s milk, soybean, wheat, Egg white, peanut, tree nuts, fish and selfish. They account for 90% of reactions.
Allergy- examination
- Skin- eczema (extent and severity), urticaria.
- Eyes- conjunctivitis, swollen, watery.
- Nose- nasal speech, congestion and inspection
- Chest- shape and wheeze.
- Growth parameters- lots of disorders which cause symptoms similar to allergies cause a failure to thrive. This could be general malabsorption.
How useful is a skin prick test
It is cheap, painless with instant results. It has a 90% sensitivity and a 50% specificity. Due to the low specificity you will get more positive results then are clinically relevant. So when examining results be aware of clinical history.
How do you use a skin prick test
You put a drop of the allergen on the skin and place a small incision in the skin within the upper epidermis and that will mimic mast cell degranulation. If there is an allergy you will get a wheel and flare rash. You then put a drop of histamine on the skin as a control, everyone will react to the histamine. You measure the size of the reaction produced.
Allergy- blood test
Specific IgE measurements looks specifically at the allergen you are investigation. Blood tests are expensive and can take a week for results to get back. Blood tests measure the levels of allergy antibodies or IgE produced when your blood is mixed with a series of allergen in the lab
When do you use an allergy blood test
You do this when there is a risk of anaphylaxis in the skin test and if there is recent antihistamine use as the skin prick test wont work. If the patient has lots of eczma you do it instead of the skin prick test.
Components test- allergy
Identifies the part of the allergen that the patient is allergic to as this will effect on the severity of the reaction. The component test can be used as a diagnosis and risk assessment
Severity of allergies- peanuts
Patients who are sensitised to the peanut allergen Ara h 8 usually experience none or very mild oral symptoms. Patients who are sensitised to more stable components such as the seed storage proteins (i.e. Ara h 2) are more likely to experience systemic reactions.
Food challenge- allergies
It is open feeding/single blinded. There is the gradual feeding of the test food under supervision and see if they react. You need specific protocols and trained staff due to the risk of anaphylaxis. It can be done at home or in the hospital.
Blood test results for allergy
Normal range for blood tests is 0-100 ku/L so over 100 is an allergy.
EpiPen
Epinephrine autoinjectors (EpiPen)- used when the patient goes into an anaphylactic shock, two of them might need to be used. They should be carried around at all times
Allergy treatment- immunotherapy
It is associated with more risk but is used when there is inadequate control or the allergen is unavoidable. Can be used for pollen, house dust and certain foods like peanuts. Anti-IgE therapy is used for asthma and chronic urticaria
Insect stings- anaphylaxis
More common in adults and males. Can cause a local reaction or anaphylaxis. It is reported in 0.3-3% of stings. Ischaemic heart disease and chronic lung disease are risk factors for severe/fatal anaphylaxis. Half of the people who die did not know they had an allergy.
Causes of anaphylaxis
Food, pollen and insect bites, medication, miscellaneous (immunotherapy) and idiopathic (don’t know the cause).
