Allergic Reactions
There are 3 main reactions: Urticaria, Angioedema and Anaphylaxis. We are just mentioning here some important points. Treatment in real practice might vary but all agree on antihistamines as the cornerstone. This post is just a summary.
Urticaria starts minutes to few hours after exposure to the etiology like food, animals, latex, insect bites and plants. Usually, last less than 24 hours and treatment of choice is 2nd generation antihistamines like cetirizine or Loratadine, i.e non-sedating. May add in severe cases H2-blockers like famotidine or tricyclic antidepressant like doxepin. When urticaria lasts more than 24 hours then think about vasculitic urticaria which can be diagnosed with skin biopsy. In vasculitic urticaria the ESR and CRP are usually elevated. Diagnosis can be associated with this are hepatitis B and C, Cryoglobulinemia, hypothyroidism, malignancy and parasitic infections if recent history of travel.
Angioedema presentation similar to urticaria but with addition of edema that can involve any body surface including skin and mucosa internally or externally. Etiology can be either (allergic) Mast cell-mediated with etiology as urticaria or Bradykinin-mediated with no urticaria with etiologies like hereditary and acquired angioedema which can be diagnosed with low C1 and C4 levels. Treat the first one with combination of epinephrine (for airway involvement), antihistamines and corticosteroids (prescribe the patient an injectable epi pen to carry for emergency). Treat the second with intravenous C1 inhibitors or FFPs for emergency situations. Prescribe danazol or stanozolol for maintenance. Bradykinin-mediated angioedema might be associated with certain conditions like lupus, lymphoma and Monoclonal gammopathy of undetermined significance (MGUS) where C1q levels are also low in addition to C1 and C4.
Anaphylaxis is severe form of the above usually starts with abdominal symptoms before progression to respiratory compromise or vascular collapse. It is IgE-mediated (anaphylactic reaction) or non IgE-mediated (anaphylactoid reaction). Serum tryptase and histamines are usually elevated. Epinephrine is the main treatment besides supportive measures which might includes steroids, fluids, bronchodilators, oxygen...
For specialized reading in these topics the Principles and Practice is a good book.
This post covers the points you need to know for your board exams as well as for teaching residents on the daily rounds. Medical professionals can't use the information here to treat their patients nor people can use the information her to treat themselves. If you are having any medical issues, contact your doctor or local emergency services.