2025 – PAGE 106 – ALLERGY & IMMUNOLOGY

IGE MEDIATED MEDICATION HYPERSENSITIVITY

Consider IgE mediated medication hypersensitivity in any patient with a pruritic rash/hives ± SOB occurring within 1 hour of the second dose of a medication.

PENICILLIN (PCN) ALLERGY

In most cases, alternative antibiotics can be used when patients are allergic to penicillin. In some cases, however, such as syphilis in pregnancy, penicillin is the best treatment. Desensitize patients with a penicillin allergy if they have SYPHILIS IN PREGNANCY or if you are presented with a CYSTIC FIBROSIS (CF) patient with resistant Pseudomonas (needing an anti-pseudomonal penicillin such as ticarcillin).

SERUM SICKNESS

Serum sickness and serum-sickness-like reactions can result in arthritis, arthralgias, nephritis or a rash within 1-2 weeks of exposure to an offending agent such as cefaclor, amoxicillin, minocycline or anti-venom. Treat by removing the offending agent if possible. Use antihistamines for pruritis and rashes, use NSAIDS for fevers, and you may use steroids for severe symptoms (e.g., high fever or arthritis) or if the patient has to continue using the offending agent (e.g., snake anti-venom immunotherapy).

BEE STINGS

Bee stings cause an IgE mediated reaction. If symptoms resolve with therapy in the ER, you may discharge the patient home. If not, admit to inpatient.

POISON IVY, POISON OAK, & POISON SUMAC

The term RHUS DERMATITIS is used to describe the skin manifestations of poison ivy, oak, and sumac. If the rash is in a sensitive area or is severe, give oral STEROIDS for 2–3 weeks. Shorter courses can result in a re-flare.

MNEMONIC: If the boards talk about exposure to a plant with three leaves, they are talking about one of the above-mentioned plants. “LEAVES OF THREE, LET THEM BE!” The answer might be RHUS DERMATITIS.

TYPES OF IMMUNITY

Types of immunity include Humoral, Cellular, Phagocytic, and Complement mediated. They are discussed below. KNOW what labs should be ordered to test the functionality of each of these different immune systems:

• HUMORAL DEFECTS: Tests include Isohemagglutinins and/or Serum IgG (or Ig subclasses from previous vaccinations such as varicella, rubella, or tetanus). Remember, these are antibody tests.
• CELLULAR DEFECTS: The primary test is a Candida Delayed-type hypersensitivityintradermal test. >10mm after 48 hours means cellular immunity is intact and primary T-cell defects are virtually excluded. If the test is negative, you can also check lymphocyte counts, T-cell subtyping with flow cytometry, or lymphocyte stimulation testing.
• PHAGOCYTIC DEFECTS: Phagocytes such as neutrophils are attracted to cytokines. Tests for chronic granulomatous disease include the generally-preferred DihydrorhodamineFluorescence Test (DHR or DHR 123) and the Nitroblue Tetrazolium dye.
  • MNEMONIC: “NEUTROblue” tetrazolium dye test
• COMPLEMENT DEFECTS: Test with a total complement assay (AKA Complement 50). This checks for early (C1–4) and late (C5–9) deficiencies.