Monday, June 20, 2011

Diarrhea Case 3

A 25-year-old woman is hospitalized for multiple injuries to her arms and legs from an automobile accident. She is treated with several intravenous broad-spectrum antibiotics because of significant concern that her wounds are becoming infected with a mixed flora of organisms. She responds over the next several days to the antibiotics with an initial decrease in fever. However, on the fourth day after her accident, she develops severe diarrhea with fever, vomiting, cramping abdominal pain, tenesmus, abdominal distension, and fluid losses severe enough to require IV fluids.
Proctoscopic examination demonstrates discrete yellow plaques up to 2 cm diameter which are scattered over the colonic mucosa. Which of the following would most likely be demonstrated on colonic biopsy?
/ A. Acid fast bacteria
/ B. Neoplastic polyps
/ C. Parasitic eggs
/ D. Pseudomembrane formation
/ E. Small granulomas
Which of the following organisms has been implicated in this disease?
/ A. Clostridium botulinum
/ B. Clostridium difficile
/ C. Clostridium perfringens
/ D. Clostridium septicum
/ E. Clostridium tetani
Q 3
Which of the following tests would be most helpful in confirming the diagnosis?
/ A. CT scan
/ B. MRI scan
/ C. "Scotch tape" test
/ D. Specific toxin in stool
/ E. Stool for ova and parasites
Q 4
This patient should not undergo barium contrast studies because of the increased risk in her disease of which of the following
/ A. AIIergic reaction
/ B. Gut perforation
/ C. Predisposition for cancerous transformation
/ D. Secondary appendicitis
/ E. Trapping of dye in diverticula
Q 5
Which of the following drugs is most likely to be effective in this case?
/ A. 3rd generation cephalosporin
/ B. Amoxicillin
/ C. Ampicillin
/ D. CIindamycin
/ E. Vancomycin

Diarrhea Case 3 Answers
The correct answer is D. This patient's history and proctoscopic examination are typical of severe pseudomembranous colitis (also sometimes called antibiotic associated colitis). Patients with milder disease may have only diarrhea. On pathologic examination, pseudomembranes composed of fibrin, neutrophils, necrotic material, and bacteria are seen overlying partially disrupted glands with prominent submucosal edema.
Acid fast bacteria (choice A) would suggest tuberculosis or atypical mycobacterial infection.
Neoplastic polyps (choice B) are seen as isolated findings or as part of familial polyposis syndromes.
Pseudomembranous colitis is not related to parasitic infection (choice C).
Small granulomas (choice E) could suggest either Crohn disease or tuberculosis.
The correct answer is B. The clostridia are gram-positive, anaerobic, spore-forming rods that can produce a variety of nasty diseases. This patient's disease, pseudomembranous colitis, is due to bacterial gut overgrowth with Clostridium difficile, usually in the aftermath of broad-spectrum antibiotic therapy. Both children and adults may become infected. Probably in most cases, the patients already had small numbers of the organisms in their guts before antibiotic therapy, although isolated examples of transmission within wards have also been documented.
Clostridium botulinum(choice A) causes botulism.
Clostridium perfringens(choice C) and Clostridium septicum(choice D) cause gas gangrene.
Clostridium tetani(choice E) causes tetanus.
The correct answer is D. Clostridium difficile produces toxins A and B, which can now be rapidly identified in stool samples. This is the best confirmatory test following proctoscopy, as the results will be back much faster than the pathology report on a tissue sample. The toxins cause necrosis of the superficial gut mucosa that, in turn, leads to pseudomembrane formation. True infection of the gut wall by the bacteria does not occur. (The bacteria like to live in and eat the necrotic material and fibrin of the pseudomembrane.)
CT scan (choice A) and MRI scan (choice B) are expensive tests that will not contribute to the diagnosis.
The "Scotch tape" test (choice C) involves using tape to collect pinworm eggs from the perirectal skin.
Clostridium difficile is a bacterium rather than a larger parasite, so stool for ova and parasites (choice E) would not be helpful.
The correct answer is B. In addition to the immediate risks related to hypotension, dehydration, and electrolyte imbalance in these sometimes critically ill patients, complications that can incur include colonic perforation (which may be induced by barium contrast studies) and toxic megacolon.
Pseudomembranous colitis does not alter allergic reactions (choice A), predispose for appendicitis (choice D) or cancer (choice C), or induce formation of diverticula (choice E).
The correct answer is E. Clostridium difficile is resistant to most antibiotics, which is why it tends to cause a bowel bacterial overgrowth when broad-spectrum antibiotics are used. The two antibiotics to which it is usually sensitive, and that are consequently most often used to treat pseudomembranous colitis, are vancomycin and metronidazole. The other agents listed in the choices are frequently reported causes of pseudomembranous colitis.


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