MARATHON for USMLE Step 1 Answers 2017 pdf

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ANSWERS
Question 1
The correct answer is A
Educational Objectives
Recall how to
differentiate ulcerative colitis from Crohns disease.
Critique
This
patient has the typical clinical findings of new-onset inflammatory
bowel disease. Based on his presentation and results of initial studies,
the type of inflammatory bowel disease cannot be established. The
differentiation of Crohns disease from ulcerative colitis cannot be made
in up to 5% of patients who present with features of indeterminate
colitis. These patients require additional testing. The most useful tests
are an assay for anti-Saccharomyces cerevisiae antibody (ASCA),
which is usually positive in patients with Crohn’s disease, and an assay
for perinuclear antineutrophil cytoplasmic antibody (p-ANCA), which is
usually positive in patients with ulcerative colitis. This patient most
likely has Crohns disease, based on ASCA positivity.
Colonic biopsy
findings of continuous pancolitis are more consistent with ulcerative
colitis, although neither granulomas nor the transmural nature of the
inflammation of Crohn’s disease may be evident on biopsy. Distal ileitis
can be found on cont rast radiographic studies in patients with either
ulcerative colitis (backwash ileitis’) or Crohns disease. No specific
findings for Crohn’s disease such as cobblestoning or fistulae are noted
in this patient. Smoking protects against ulcerative colitis but often
aggravates the course of Crohn’s disease, and patients with ulcerative
colitis are sometimes first diagnosed soon after they quit smoking.
Question 2
The correct answer is D
 Educational Objectives
Recall the
diagnostic tests for acute hepatitis A virus infection. Critique
This patients clinical and biochemical findings suggest acute hepatitis.
She has recently returned from a country where hepatitis A virus is
endemic, and testing for IgM antibody to hepatitis A virus (IgM anti-
HAV) is indicated.
A positive test for antibody to hepatitis B surface
antigen (anti-HBS) indicates only that the patient has been exposed to
HBV. It does not indicate that she has acute HAV infection. There is
nothing in the history to suggest acute hepatitis C virus infection. In
addition, determination of antibody to hepatitis C virus (anti-HCV) is
not the appropriate test to diagnose this infection, as up to 40% of
patients may have a negative test. The clinical picture is not consistent
with an amebic liver abscess, and serum aminotransferase elevations
to the degree noted in the patient are not typical for amebic liver
disease. Therefore, an indirect hemagglutination test for Entamoeba

histolytica is not indicated. Acute Epstein-Barr virus infection is usually
associated with pharyngeal discomfort, lymphadenopathy, and atypical
lymphocytosis, which this patient does not have.
Question 3
 The correct answer is E
 Educational Objectives
Recall how to
manage a patient with uncomplicated gastroesophageal reflux disease.
Critique
This patient has the classic symptoms and findings of uncomplicated
gastroesophageal reflux disease (GERD). A response to acid
suppressive therapy is the best way to confirm the diagnosis, since
additional testing is not indicated if the patient’s symptoms resolve
with therapy.
Upper endoscopy is usually indicated only for patients
with complications of GERD. Patients with such complications usually
present with warning symptoms (dysphagia, odynophagia, weight loss,
and/or anemia), none of which the current patient has. Esophageal
manometry is used to diagnose esophageal motility disorders or to
evaluate patients prior to antireflux surgery. Ambulatory 24-hour
esophageal pH monitoring is indicated for patients who do not respond
to initial acid suppressive therapy or who may have a diagnosis other
than GERD. Barium swallow is used in the evaluation of esophageal
function and in assessing structural abnormalities of the esophagus.
Question 4 
The correct answer is A 
Educational Objectives
Recall the most
appropriate initial management for a patient with acute upper
gastrointestinal bleeding.
Critique
Upper endoscopy should not be performed immediately because the
patient must be resuscitated, stabilized, and intubated for airway
protection prior to this procedure. If upper endoscopy is done
immediately, the patient is at high risk for aspiration or
othercardiopulmonary complications.
Gastroenterology and Hepatology:Question 5
The correct answer is A
Educational
Objectives
Recall how to use the MELD score and the Child-Turcotte-
Pugh score to prioritize patients for liver transplantation.
Critique
In February 2002 the United Network for Organ Sharing adopted the

 

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