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    Immunologic Hypersensitivity Reactions: Key Guidelines for Internists

    Immunologic hypersensitivity reactions reflect immune-mediated tissue injury seen in allergies, autoimmune disease, and other inflammatory diseases. These immune responses are the staggeringly important basis for disease prevention in the body, and are the normal reaction to a foreign antigen. There are 2 general dysfunctions in which these normal defense mechanisms cause disease:

      1. An overexuberant response to a foreign antigen
      2. Autoimmune disease develops, in which the body sees a self-antigen as foreign

    As an internal medicine physician, staying up to date on the latest clinical guidelines and best practices is essential, especially when it comes to managing hypersensitivity reactions. These reactions are common and can be life-threatening, requiring swift and accurate intervention.

    This blog uses a snippet from our Internal Medicine Video Board Review lectures to refresh your knowledge on hypersensitivity reactions—with a particular focus on anaphylaxis—to help you better prepare for both patient encounters and board exams. In this excerpt, Dr. Patel presents a clinical scenario and reviews guidelines for hypersensitivity reactions. 

    This video is an excerpt from our 2024–2025 Internal Medicine Video Board Review. For a deeper review into Allergy & Immunology, plus 39+ more hours of board-focused lectures, explore our Video Board Review.


    Audience response question (00:00–00:37)

    You have a 45 year old man with a history of peanut allergy. Develop shortness of breath and abdominal pain after accidentally eating a cookie containing peanuts. Blood pressure is 130 over 80, heart rate is 110 beats per minute. On exam, we see audible wheezes and skin exam is normal. What would be the most appropriate next step?

            1. Give albuterol
            2. Give diphenhydramine 
            3. Give solumedrol 
            4. Give epinephrine
            5. Observation only.

    Go ahead and key in your responses there for me.

    Audience response answer and explanation (00:38–1:30)

    All right. So the answer is D—Give epinephrine. Great work there because he is having anaphylaxis, right. This patient has 2-organ involvement after consuming a known allergen; therefore, he has anaphylaxis. The first line treatment of anaphylaxis is epinephrine, epinephrine and epinephrine.

    Albuterol would have helped with the bronchoconstriction. But epinephrine is still the first line choice. Diphenhydramine will help, but it's not first line. Solumedrol—corticosteroids—help with the late phase reaction, but again, they're not first line treatment.

    Epinephrine is the only first line treatment for anaphylaxis. Observation alone would have been insufficient for this patient because he is experiencing anaphylaxis.

    Hypersensitivity reactions (01:30–02:25)

    So, if we take a look at our hypersensitivity reactions, we have four types of hypersensitivity reactions.

    Type 1 is our immediate hypersensitivity reaction, which is IgE-mediated. Onset is usually within seconds to an hour after exposure.

    You have Type 2 hypersensitivity reactions, which are your cytotoxic reactions. These are mediated by IgG or IgM. Onset is usually after days of exposure. 

    You have Type 3 hypersensitivity reactions. These are your immune complex reactions. It's an antibody-antigen complex. This takes weeks to develop. So it occurs weeks after the trigger.

    And then you have your Type 4 delayed hypersensitivity reactions, which are T-cell-mediated. These usually occur 48 to 96 hours after the trigger. And we're going to be talking about each of these individually.

    Type 1 — Immediate Hypersensitivity (02:26—02:58)

    If we take a look at type one immediate hypersensitivity reactions, again, this occurs very quickly after the exposure—seconds to an hour. This is IgE-mediated, mediated by your allergic antibody immunoglobulin E. Classic examples would be things that I normally see in the office, your typical allergies: food allergies, asthma, allergic rhinitis, latex allergies, urticaria. These are classic examples of IgE-mediated Type 1 hypersensitivity reactions.

    Anaphylaxis (02:59—02:58)

    So if we take a look at anaphylaxis specifically, this is a life-threatening IgE-mediated reaction. Common causes include antibiotics such as penicillins, cephalosporins. If we take a look at foods, common culprits might be peanuts, tree nuts, fish, and shellfish. Latex allergies in health care workers. You might see patients who've had spina bifida or urogenital malformation because they've had a lot of surgeries. They've had a lot of manipulation where the surgeon is going in with those latex gloves. And that's why they're also more prone to latex allergies. Anesthetic agents such as induction agents, neuromuscular blocking agents, and insect stings—these are all common causes of anaphylaxis.


    Dr. Patel's clinical scenario and review of the guidelines underscore the importance of prompt and appropriate treatment, particularly the use of epinephrine as the first-line intervention in cases of anaphylaxis. By staying current with clinical guidelines and continually refreshing your knowledge with Internal Medicine Video Board Review, you can ensure that you are prepared to deliver the highest standard of care to your patients and take on any board exam.

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