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The Anatomy of a USMLE Question

Answering USMLE questions correctly requires a profound amount of both knowledge and test-taking skill. While a solid knowledge base is essential for a high score, honing in on how the test is written can help you maximize your performance and eliminate incorrect answers for those questions that you find particularly difficult. Let’s take a deep dive into how a USMLE-style question is written.

The Clinical Vignette

Almost every USMLE-style question is written in a case format and typically follows the same classic order:

  1. Chief concern

  2. Past medical history

  3. Medications

  4. Allergies

  5. Social history

  6. Diagnostics

  7. Physical exam

  8. The question being asked

Every question has a testable concept that it is trying to test the reader on. Let’s think about how questions are written so we can better understand how to approach them.

Questions are Often Reverse-Engineered

What this means is that many questions writers start with the correct answer and a compelling differential diagnosis. A properly written USMLE question will often have a differential that is highly relevant and something that the clinician must consider when presented with a chief concern. For example:

Tested concept: Pes anserine bursitis occurs in overweight woman and athletes and presents with tenderness to palpation over the medial aspect of the tibia just inferior to the patella.

Answer choices (differential diagnosis):

  1. Per anserine bursitis

  2. ACL tear

  3. PCL tear

  4. Medial meniscus tear

  5. MCL tear

  6. Osteoarthritis

  7. Patellofemoral syndrome

Now, with this differential in mind, the author will create a story that makes the correct answer the most likely diagnosis while making the other diagnoses compelling but less correct. Remember – all answer choices are on a spectrum of correctness. You’ll never see a testable concept of threatened abortion with an answer choice of penile fracture! Similarly, if there is not enough information to make a definitive diagnosis, you should pick the answer choice that is the most epidemiologically plausible.

With this in mind, the author will now add in information to the case that makes each diagnosis more or less compelling:

A 22-year-old obese woman presents to her doctor with knee pain. She recently joined her school’s basketball team and felt pain in her knee when she was suddenly pivoting during a play. Since then she has not been able to play basketball secondary to the pain. She states that her knee is in pain and she does not feel comfortable bearing weight on it, and she struggles to go up and down stairs. On physical exam, the patient has profound tenderness on palpation over the superior and medial aspect of the tibia just inferior to the patella. Her gait is stable and does not appear to be antalgic. The rest of her exam is within normal limits. Which of the following is the most likely diagnosis?

As you can see, this question has compelling evidence to support each incorrect answer. For example, obesity + joint pain is a classic presentation for osteoarthritis; however, this typically occurs in older patients and is not sudden in onset thus ruling out this answer. Similarly, the mention of symptoms near the patella, and pain with climbing of stairs was deliberately included for patellofemoral syndrome; however, there is no physical exam finding of pain with compression of the patella – the pain is inferior and medial to the patella. Finally, the sudden onset of pain with pivoting/twisting is classic for an ACL, MCL, PCL, or a meniscus tear. The reader may see this classic phrase and pick the most epidemiologically relevant answer which would be an ACL tear; however, this ignores the key information the author included (or did not include) to rule out the diagnosis. In this case, you are given only 1 finding on physical exam and no other findings which would support a diagnosis of a ligament or meniscus tear. Given that the rest of the physical exam aside from this one finding was “within normal limits” the most plausible answer choice is pes anserine bursitis as it fits the epidemiological picture and symptoms/findings given. As you can see in this case, the differential diagnosis is laid out and then information is then added to make certain answers more or less compelling.

Special Cases

When designing a board question it must be consistent with the classic epidemiological presentation that the disease would present with. This means that if you are asked what the cause of a runny nose is during the winter, the answer will be rhinovirus or coronavirus and not some odd presentation of malaria even with a recent travel history. There are a few instances when this is not true:

  1. A finding is given that concretely rules out that diagnosis

  2. The most accurate test rules in another diagnosis

Let’s use gout as an example:

An alcoholic, obese, thiazide-diuretic using patient presents with severe pain of the great toe right after winning a meat-eating competition. Aspiration of the joint reveals rhomboid shaped crystals. What is the most likely diagnosis?

This case is CLASSIC for gout; however, you are given the results of a “most accurate test” which demonstrates rhomboid shaped cells rather than negatively birefringent cells which would be seen in gout. In this case, you must choose pseudogout as the most likely diagnosis! Similarly, if aspiration of the joint was within normal limits then you would be forced to rule out gout and find another cause such as osteoarthritis in this patient.

In summary remember these key points:

  1. All answer choices are written on a spectrum of correctness.

  2. The information in the case is given specifically to rule in or out a diagnosis.

  3. Questions are often reverse engineered to include information to make each choice correct on some level.

  4. If there is not enough information to definitively answer the question, pick the answer that is the most epidemiologically common.

  5. Never forget to respect the results of the most accurate test!

There are many strategies you can now employ when reading a question. I personally choose to read the question stem first (the last sentence) to frame my thinking and look for specific information that rules in or out a certain diagnosis. Some authors prefer to start with the case; however, the key takeaway point is to remember that the USMLE blatantly includes each piece of information to help you make the diagnosis. If you find yourself stuck, ask yourself – “Why did they include this piece of information?”, as sometimes, simply answering this question for yourself can be enough to allow you to choose the correct answer.

Damian Apollo is a resident in Emergency Medicine at the Harvard-affiliated Beth Israel Deaconess Medical Center. He obtained his MD and MBA from Yale, and scored a 252 on Step 1 and a 261 on Step 2 CK. He tutors with USMLE Pro for Step 1, Step 2 CK, Step 2 CS, and Shelf Exams, and is a residency application advisor for Emergency Medicine.

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1 Comment

May 25, 2020

This is one of the very well written blog posts with emphasis on how to deconstruct usmle vignette .It was very clear ,concise and to the point. looking forward to more Damian Apollo blog posts especially "The Anatomy of Usmle qn ---Part 2"---updated version. Thank you . Dr.Sailaja Sanikommu M.B.B.S

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