2025 – PAGE 104 – ALLERGY & IMMUNOLOGY

(DOUBLE TAKE) LACTOSE INTOLERANCE (AKA LACTASE DEFICIENCY)

It is not common for kids < 5 years old to have lactose intolerance (AKA lactase deficiency). So, for the pediatric boards, if the child is less than 5 years of age, suspect a different diagnosis!

• SYMPTOMS: Diarrhea ± abdominal pain.
• The HYDROGEN BREATH TEST can be used to help diagnose a lactase deficiency (as well as bacterial overgrowth). When the patient takes a carbohydrate load; if he or she is unable to digest the carbs because of a lack of lactase, the bacteria will digest the carbs and release hydrogen (which can be measured in the breath).
• TREATMENT: SOY milk. It does not contain lactose. It contains sucrose.
• PEARLS: Stool is NOT malodorous and does NOT have food particles. These patients do NOT vomit and do NOT have an associated rash. consider the diagnosis of an ALLERGY if you’re presented with a patient with such symptoms.
• MNEMONICS: “LACTose comes from the LACTating breasts of women and cows, NOT from soybeans.”

IMMUNOLOGY

KEY PEARL: There is a TREMENDOUS overlap within the immunodeficiency (ID), metabolic, immunologic, inborn errors of metabolism, and genetic sections. Therefore, the entire immunodeficiency section is highly represented on the exam in the form of answer choices. Knowing the pertinent positive AND negative findings is key to narrowing your choice down to one.

EPINEPHRINE PEN

Epinephrine pens (autoinjectors) are for patients with a history of severe allergic reactions or a history of anaphylaxis due to environmental exposures. Prescribe 3 sets of epinephrine pens. These should be kept at room temperature and used on the outer thigh. Replace the epinephrine pen after expiration (usually 6 months). Epinephrine pens are prescribed as a set of two in case the response is inadequate after the first injection and in case the first one had a mechanical failure of any type. Multiple sets are prescribed in order to make sure that one set is available at all times (home, school, for carrying around, etc.).

TYPES OF HYPERSENSITIVITY REACTIONS

• Type 1 Hypersensitivity reaction= IgE = Anaphylactic. Think of PCN allergy. PCN is the only antibiotic that can be skin tested. If a reaction occurs > 24 hours after PCN is administered, it is NOT a PCN allergy and there is NO indication for skin testing. Skin testing done in obscure cases typically results in > 90% of cases being ruled out as PCN allergy.
• Type 2 = AntiBody mediated = B-cell = Humoral
• Type 3 = Immune complexes, as in serum sickness or vasculitis
• Type 4 = T-cell mediated/Cellular immunity. The classic example is poison ivy. This includes CD4 cells and problems that arise from HIV/AIDS.
• MNEMONICS:
  • “1= A = Anaphylactic” or “1 = IgE = 1gE”
  • “2= B = antiBody” = humoral
  • “3= C = immune Complex”
  • “4= D = CD4 = T-cell mediated. Or, if presented with the classic example of poison “IV” = the Roman numeral IV = Type 4.