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USMLE® Step 1 questions

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A 78-year-old female presents to the emergency department with altered mental status. She was found down by her neighbors, who immediately called EMS. Medical history is notable for multiple myeloma, for which she is currently undergoing treatment. Temperature is 38.9°C (102°F), pulse is 137/min, respirations are 26/min, blood pressure is 87/60 mmHg, and O2 saturation is 89% on room air. Physical exam reveals a cachectic, ill-appearing woman who is moaning and unable to provide further history. She has bilateral costovertebral angle tenderness to palpation as well as warm and perfused peripheral extremities. Subsequent blood cultures grow a Gram-negative rod. Which of the following is the most likely trigger of this patient’s clinical presentation?

External References

First Aid








Anaphylaxis p. 110

blood transfusion p. 110

complement and p. 104

epinephrine for p. 243

IgA-containing products p. 114

shock with p. 321

Epinephrine p. 243

for anaphylactic reaction p. 112


Anaphylaxis comes from the greek word “ana-“ which roughly means against and “phylaxis” which means protection, implying that someone’s immune system has reacted to something in such a way that ends up damaging them, instead of protecting them.

It’s basically a severe type of allergic reaction that affects multiple organ systems and it’s potentially life-threatening.

Normally, the immune system recognizes and acts against pathogens that can cause disease.

These pathogens have specific molecules on their surface, called antigens, and they help trigger an immune response.

In some individuals, though, the immune system overreacts and starts targeting harmless molecules that don’t cause any problems for most people.

These include molecules found in foods like peanuts and shellfish, medications like antibiotics, and in the venom of insect bites.

In most cases, there might be a mild to moderate allergy, but sometimes things get really serious, involving two or more organ systems, and at that point it’s called anaphylaxis.

Anaphylaxis, just like any allergic response, happens in two steps, a first exposure, or sensitization, and then a subsequent exposure, which is when it actually gets a lot worse.

So, let’s say a person is stung by a bee from a nearby beehive, for the first time in their life.

When the bee pierces the skin with its stinger, its venom gets into the skin.

Part of that venom molecule can get picked up by a dendritic cell, which is a type of immune cell.

The dendritic cell gobbles up the foreign particle and presents it to a nearby lymphocyte, called a T cell.

If the T cell is activated, it starts to produce cytokines, which stimulate B cells, another group of lymphocytes, which produce IgE antibodies.

These IgE antibodies get released into the bloodstream and bind to the surface of mast cells and basophils, which are immune cells that are full of granules that contain proinflammatory molecules.


Anaphylaxis is an acute, generalized, multi-systemic allergic reaction to an antigen such as a bee sting. Its symptoms can range from mild pruritus and skin flushing to severe respiratory distress and cardiovascular collapse. Anaphylaxis can lead to rapid deterioration, and without treatment, it can lead to respiratory failure and cardiovascular collapse, and then death.


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  2. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  3. "Yen & Jaffe's Reproductive Endocrinology" Saunders W.B. (2018)
  4. "Bates' Guide to Physical Examination and History Taking" LWW (2016)
  5. "Robbins Basic Pathology" Elsevier (2017)
  6. "Anaphylaxis: A review of causes and mechanisms" Journal of Allergy and Clinical Immunology (2002)
  7. "Pathophysiology of anaphylaxis" Current Opinion in Allergy & Clinical Immunology (2011)
  8. "Anaphylaxis: mechanisms and management" Clinical & Experimental Allergy (2011)

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