USMLE® Step 1 Question of the Day: A Syncopal Event

USMLE® Step 1 Question of the Day: A Syncopal Event

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Each week, Osmosis shares a USMLE® Step 1-style practice question to test your knowledge of medical topics. Today’s case involves a 65-year-old man after a syncopal event at home. Can you figure out the diagnosis?

A 65-year-old man presents to the emergency department after a syncopal event at home. He has had two hours of left-sided flank pain radiating to the groin, which is associated with nausea and vomiting. Prior to this episode, he reports vague back pain and fatigue over the past several months. His past medical history is significant for 80-pack-year smoking history, hypercholesterolemia, and hypertension. He has had no previous abdominal surgeries. His BMI is 30 kg/m2. His temperature is 37.0 °C (98.6 °F), pulse is 100/min, respirations are 20/min, blood pressure is 90/60 mmHg, and O2 saturation is 95% on room air. Abdominal examination shows distension and diffuse tenderness on palpation, and cardiovascular examination shows a 1+ dorsalis pedis pulse in the left foot and 2+ pulse in the right foot. Laboratory findings show a WBC of 12,000/mm3. Which of the following is the most likely diagnosis?

A. Renal colic

B. Acute pancreatitis

C. Bowel obstruction

D. Abdominal aortic aneurysm

E. Cholangitis

Scroll down to find the answer!

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The correct answer to today’s USMLE® Step 1 Question is…

D. Abdominal aortic aneurysm

Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!

Incorrect answer explanations

The incorrect answers to today’s USMLE® Step 1 Question are…

A. Renal colic

Incorrect: Renal colic commonly causes flank pain radiating to the groin with associated nausea and vomiting; however, it rarely causes syncope. Patients commonly describe sharp severe flank pain with associated urinary symptoms, including dysuria and hematuria.

B. Acute pancreatitis

Incorrect: Pancreatitis can present with nausea and vomiting, but it is also commonly associated with distinct mid-epigastric pain radiating to the back and a history of chronic right upper quadrant pain due to gallstones or recent alcohol use, neither of which this patient endorses.

C. Bowel obstruction

Incorrect: Bowel obstructions may present with abdominal distension and pain, as well as nausea and vomiting. They are most commonly associated with a history of adhesions from prior abdominal surgeries. This patient has no past surgical history, making this diagnosis less likely.

E. Cholangitis

Incorrect: Cholangitis refers to an ascending infection of the biliary tree. This disease classically presents with right upper quadrant tenderness, fever, and jaundice, referred to as Charcot’s triad. While the patient in this vignette has signs of sepsis including hypotension and tachycardia, there is no evidence of fever or jaundice, making this diagnosis less likely.

Main Explanation

Abdominal aortic aneurysms (AAA) should be considered in any older individual presenting with sudden onset abdominal, low back, or flank pain and a history of syncope with hypotension. Risk factors for AAA include significant age >65 yearssmoking, male genderfamily history of AAA, and other risk factors for coronary artery disease or peripheral vascular disease including hypertension and hypercholesterolemia. Abdominal aortic aneurysms are true aneurysms, meaning all three layers of the blood vessel – the intima, media, and adventitia – are dilated. The pathophysiology of abdominal aortic aneurysms is a complex, multifactorial process that involves alterations in the structure of the vascular wall due to inflammatory changes, abnormal collagen remodeling and cross-linking, as well as loss of elastin and smooth muscle cells. This ultimately results in progressive thinning and weakening of the aortic wall and enlargement of the aortic diameter to a dilation 50% greater than the normal diameter of the aorta.

AAAs commonly occur at the infrarenal level, or below the level of the renal arteries. People with near rupture or rapid expansion of an AAA commonly present with sudden onset back, flank, or abdominal pain and associated symptoms such as nausea and vomiting, mimicking a myriad of other conditions. Other associated symptoms may include diminished peripheral pulses due to expansion of the aneurysm compressing the internal iliac arteries. Although a pulsatile abdominal mass is a classic presentation, it may not always be detectable, especially if the patient is obese, such as in this vignette. If left untreated, AAAs can rupture, leading to severe hypotension, hemodynamic instability, and death. In a case where rupture has not occurred, repair should be offered when the aneurysm is >5 cm.

Major Takeaway 

Abdominal aortic aneurysms (AAA) classically present with a triad of hypotension, abdominal, low back, or flank pain, and a palpable pulsatile mass, although the findings of all three is a rare clinical occurrence. Primary risk factors include age >65 years, smoking, male gender, and a family history of AAATreatment should be offered to patients with AAA >5 cm, as risk of rupture increases exponentially beyond this value.

References

Chaikof EL, Dalman RL, Eskandari MK, et al. The Society for Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm. J Vasc Surg. 2018;67(1):2‐77.e2. doi:10.1016/j.jvs.2017.10.044

Kumar, V., Abbas, A. K., Aster, J. C., & Robbins, S. L. (2013). Robbins Basic Pathology Philadelphia: Elsevier/Saunders

Abdominal Aortic Aneurysms, K. Craig Kent, M.D.November 27, 2014 N Engl J Med 2014; 371:2101-2108 DOI: 10.1056/NEJMcp1401430

Curry, M. (2017, May 18). Rosen’s Emergency Medicine: Concepts and Clinical Practice. Retrieved from https://www.us.elsevierhealth.com/rosens-emergency-medicine-concepts-and-clinical-practice-9780323354790.html.

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The United States Medical Licensing Examination (USMLE®) is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). Osmosis is not affiliated with NBME nor FSMB. 


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