If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 3 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.
This month’s stumper
A 74-year-old man with insulin-dependent diabetes mellitus and chronic renal failure comes to the emergency department because he has been nauseated and vomiting for 24 hours. He denies any chest pain or abdominal pain. He underwent his routine hemodialysis yesterday without any complications.
The man’s temperature is 38.8 ºC (101.8 ºF), blood pressure is 120/70 mm Hg, and pulse is 110 beats per minute. Abdominal examination reveals guarding in the right upper quadrant with no tenderness or peritoneal signs. Laboratory studies show a leukocyte count of 24,000/mm3 and a serum bilirubin of 2.2 mg/dL. Ultrasound examination of the right upper quadrant fails to reveal gallbladder stones.
Which of the following is the best next step in the management of this patient?
A. Order a CT scan of the abdomen.
B. Order a colonoscopy.
C. Order a hepatobiliary iminodiacetic acid (HIDA) scan.
D. Order intravenous antibiotics and continued observation.
E. Order an upper GI endoscopy.
The correct answer is C.
Kaplan Medical explains why
The HIDA scan is the most accurate diagnostic test for diseases of the hepatobiliary tree, and it will confirm the diagnosis. Acalculous cholecystitis is associated with a variety of conditions, including diabetes, trauma, mechanical ventilation, burns, childbirth and many others.
These patients may not present with classical signs of cholecystitis; signs and symptoms will depend on the underlying predisposing clinical condition. Acalculous cholecystitis is characterized by the absence of gallstones and sometimes even by biliary sludge.
Ultrasound is the method of choice to make the diagnosis, since it can visualize the gallbladder and also the liver, pancreas, and kidneys. Ultrasound will reveal a thickened gallbladder wall, pericholecystic fluid, gas within the gallbladder wall and evidence of surrounding inflammation. If the ultrasound fails to make the diagnosis, a HIDA scan may be useful.
Why the other answers are wrong
Choice A: Ordering a CT scan of the abdomen will not add much to the diagnosis. This patient’s clinical presentation is clearly associated with the biliary tract, and if the ultrasound fails to reveal the diagnosis, CT scan is not the imaging method of choice to observe the biliary tract.
Choice B: Colonoscopy is not helpful in the workup of biliary symptoms.
Choice D: Intravenous antibiotics are indicated to treat cholecystitis, but in the presence of gangrene or unresponsive cholecystitis, surgery is indicated. Continued observation may result in worsening of the symptoms and signs and the development of complications such as systemic sepsis; therefore, observation and administering antibiotics alone is not the best option at this time. Further evaluation is required.
Choice E: An upper gastrointestinal endoscopy helps in the diagnosis of pathology in the stomach or duodenum, but will not be helpful in this patient.
Tips to remember
- Acalculous cholecystitis is associated with a variety of conditions, including diabetes, trauma, mechanical ventilation, burns, childbirth, and many others.
- It is marked by the absence of gallstones and sometimes even biliary sludge.
- Ultrasound is the modality of choice for diagnosis.
- If it is equivocal, then a HIDA scan is the next best option.
For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.
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