If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 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 34-year-old man comes to the physician because of diarrhea and flatulence for three months. He has had a 33-lb (15-kg) weight loss over the same time period. His diet consists of dairy, meat, grain, and vegetable products. His temperature is 36.5°C (97.8°F), pulse is 70/min, respirations are 15/min, and blood pressure is 115/75 mm Hg. Fecal occult blood test is negative. Upper endoscopy with biopsy shows marked atrophy of duodenal villi.
Concurrent serological studies will most likely reveal which of the following?
A. Antibodies to cyclic citrullinated peptide.
B. Antibodies to Helicobacter pylori.
C. Antibodies to mitochondria.
D. Antibodies to smooth muscle.
E. Antibodies to tissue transglutaminase.
The correct answer is E.
Kaplan Medical explains why
Serologic screening for anti-tissue transglutaminase IgA antibodies is sensitive and specific for celiac disease:
- Duodenal biopsy: flattened villi.
- Etiology: allergic, immunologic, or toxic reaction to the gliadin component of gluten (from wheat, barley, rye and related grains).
- Other serologic tests include anti-gliadin (IgA or IgG) and anti-endomysial (IgA) antibodies.
- The flattening of villi reduces intestinal surface area and thereby impairs digestion and absorption.
- Undigested or partially digested nutrients pass through the small intestine to the colon, where they are acted on by bacteria to cause diarrhea and flatulence.
- The symptoms and pathologic changes usually reverse with the complete removal of gliadin from the diet.
Why the other answers are wrong
Choice A: Antibodies to cyclic citrullinated peptide (choice A), along with the presence of rheumatoid factor, are seen with rheumatoid arthritis. Patients present with symmetric tender, swollen, warm joints of the hands and wrists. Other joints of the knees, ankles, and elbows can also be involved. Subcutaneous rheumatoid nodules are present near the elbows. There is no direct connection between rheumatoid arthritis and celiac disease.
Choice B: Helicobacter pylori infections are responsible for the majority of gastric and duodenal ulcers seen in patients with peptic ulcer disease. Upper endoscopy failed to reveal such a lesion in the gastric antrum or the proximal duodenum. Villous atrophy is not related to Helicobacter infection.
Choice C: Anti-mitochondrial antibodies are found in the majority of patients with primary biliary cirrhosis (PBC). This autoimmune condition more commonly affects older females (age 40-60 years), primarily involves the intrahepatic biliary tracts, and causes lymphocytic and granulomatous destruction of bile ducts. There is no association with celiac disease.
Patients may also present with fat malabsorption and steatorrhea, similar to our patient, from lack of bile secretion into the GI tract. However, patients with celiac disease have a more broad nutritional deficiency and marked weight loss.
Choice D: Anti-smooth muscle antibodies are seen in autoimmune hepatitis. Females are more affected than males. Patients can also have elevated anti-nuclear antibodies (ANA) and present with fatigue and jaundice.
Tips to remember
- Celiac disease: weight loss, diarrhea, and flattening of the villi.
- Antibodies: anti-tTG, anti-gliadin, and anti-endomysial antibodies.
For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.
The AMA and Kaplan have teamed up to support you in reaching your goal of passing the USMLE® or COMLEX-USA®. If you're looking for additional resources, Kaplan provides free access to tools for pre-clinical studies, including Kaplan’s Lecture Notes series, Integrated Vignettes, Shelf Prep and more.
