Allergy Flashcards
FPIES
Food protein-induced enterocolitis is not Ig-E mediated, but an example of cell mediated hypersensitivity.
It presents with irritability and protracted vomiting or diarrhoea usually 1-3 hours after feeding, and chronically can cause bloody diarrhoea and bloating.
Diarrhoea stops with cessation of enteral feeds
Hypotension occurs in about 15%.
Can present shocked
- FPIES can result in an elevated WCC with neutrophilia and left shift +/- fever so can look like sepsis
Type IV reactions
Type IV reactions (i.e. delayed hypersensitivity reactions, cell-mediated immunity) are mediated by T cells rather than by antibodies.
They produce more indolent symptoms (cachexia, early satiety, V&D, abdo pain).
IgE-mediated immediate-onset food sensitivity
Type I reactions (i.e. immediate hypersensitivity reactions) involve IgE–mediated release of histamine and other mediators from mast cells and basophils, which are the key mediators in anaphylaxis.
Continuous or repeated exposure to an can result in chronic allergic inflammation.
Tissue from sites of chronic allergic inflammation contains eosinophils and T cells (particularly TH2 cells).
Eosinophils can release many mediators (e.g. major basic protein), which can cause tissue damage and thus increase inflammation. This can result in structural and functional changes to the affected tissue.
Furthermore, a repeated allergen challenge can result in increased levels of antigen-specific IgE, which ultimately can cause further release of IL-4 and IL-13, thus increasing the propensity for TH2 cell/IgE–mediated responses.
Type II reactions
Type II reactions (i.e. cytotoxic hypersensitivity reactions) involve immunoglobulin G or immunoglobulin M antibodies bound to cell surface antigens, with subsequent complement fixation. E.g. transfusion reactions and hemolytic anemias.
Bee stings- large local reaction
Large local reactions develop over hours to days, and involve swelling of extensive areas >10 cm that are contiguous with the sting site, and may last for days.
Localised skin responses to biting insects are likely caused by vasoactive or irritant materials derived from insect saliva (not IgE), thus antihistamines may not have a significant response except for symptom control of itch.
For local cutaneous reactions, treatment with cold compresses, topical medications to relieve itch and occasionally the use of a systemic antihistamine or oral analgesic are appropriate.
Steroids may have some effect in reducing inflammation but are not required. Remove any sting present by scraping.
The risk of a systemic reaction after a large local reaction is only 5-10%, thus, venom immunotherapy is not recommended and carrying an Epipen is considered optional
Food protein enteropathy
- This is also a non IgE mediated response to food similar to coeliac disease, although less severe.
- It is distinct from FPIES in that patients do not present with lethargy, pallor, dehydration. Can present with vomiting/diarrhoea
