USMLE MARATHON Answers for step 1 PDF


Question the correct answer is A
Educational Objectives
Recall how to differentiate ulcerative colitis from Crohns disease.
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.

USMLE MARATHON Answers for step 1 PDF