MKSAP quiz on gastroenterology

The following cases and commentary, which focus on gastroenterology, are excerpted from ACP's Medical Knowledge Self-Assessment Program (MKSAP 18). MKSAP 18 Part A was released this summer. Part B will be released in print on Dec. 31, 2018, and in digital format on Jan. 31, 2019.

Case 1: Bloody diarrhea

A 24-year-old man is evaluated in the emergency department for a 2-week history of worsening bloody diarrhea with up to 10 bloody bowel movements per day. He also reports increasing lower abdominal pain and distension and that stool frequency has decreased over the past day. He has extensive ulcerative colitis of 5 years' duration. His medications are infliximab and azathioprine.

On physical examination, the patient appears ill. Temperature is 38.3 °C (101 °F), blood pressure is 90/60 mm Hg, and pulse rate is 110/min; other vital signs are normal. The abdomen is distended with guarding. Bowel sounds are hypoactive.

Laboratory studies show a hemoglobin level of 10 g/dL (100 g/L), leukocyte count of 16,000/μL (16 × 109/L), and blood urea nitrogen level of 26 mg/dL (9.3 mmol/L).

MKSAP 18 image  American College of Physicians
MKSAP 18 image © American College of Physicians

An abdominal radiograph is shown.

Which of the following is the most appropriate next step in management?

A. Colectomy
B. Colonoscopy
C. CT of the abdomen
D. Stool culture

View correct answer for Case 1

Case 2: Hematochezia in a healthy young patient

A 36-year-old man is evaluated in the emergency department after passing three bowel movements of red to maroon–colored blood. He recently injured his knee playing soccer and has been taking ibuprofen three times a day for a week. He has no other relevant medical history and does not smoke or drink alcohol.

On physical examination, he is lightheaded but alert. His blood pressure is 80/60 mm Hg, pulse rate is 126/min, respiratory rate is 12/min, and oxygen saturation is 98% breathing ambient air. Cardiac examination shows tachycardia. Rectal examination shows maroon-colored stool. All other findings are unremarkable.

The patient's vital signs improve after he is given intravenous hydration.

Laboratory studies show a hemoglobin level of 9 g/dL (90 g/L) upon presentation. Six hours later, the hemoglobin level is 7.4 g/dL (74 g/L).

Which of the following is the most appropriate test to perform next?

A. Angiography
B. Capsule endoscopy
C. Colonoscopy
D. Upper endoscopy

View correct answer for Case 2

Case 3: Blood, chills, fevers

An 80-year-old man is evaluated in the emergency department after a bowel movement with initial passage of brown soft stool followed by a large volume of red blood. He reports intermittent chills and fevers over the past week. He also has peripheral vascular disease, hypertension, and hypercholesterolemia. His history includes an aortoiliac aneurysm treated with an aortic bifurcation graft 3 years earlier. His medications are atorvastatin, hydrochlorothiazide, losartan, and low-dose aspirin.

On physical examination, the patient is comfortable. His temperature is 38 °C (100.4 °F), blood pressure is 108/60 mm Hg, pulse rate is 112/min, and respiration rate is 18/min.

Cardiopulmonary examination is unremarkable. There is midabdominal tenderness to palpation. Rectal examination reveals bright red blood mixed with brown stool.

Laboratory studies show a hemoglobin level of 9 g/dL (90 g/L). Leukocyte count is 14,000/μL (14 × 109/L) with neutrophilia.

Which of the following is the most appropriate test to perform next?

A. CT scan with contrast
B. Mesenteric angiogram
C. Tagged red blood cell scintigraphy
D. Upper endoscopy

View correct answer for Case 3

Case 4: Sudden-onset abdominal pain

A 60-year-old woman is admitted to the hospital with sudden-onset, cramping abdominal pain of moderate severity in the right lower quadrant, followed several hours later by a bloody bowel movement. She has coronary artery disease; medications are atorvastatin, metoprolol, sublingual nitroglycerin, and low-dose aspirin.

On physical examination, the patient appears comfortable. Pulse rate is 110/min; BMI is 35. Other vital signs are normal. The abdomen is nondistended with normal bowel sounds. Deep palpation elicits tenderness in the right lower quadrant with no rebound or guarding.

A CT scan without contrast shows thickening of the ascending colon. Colonoscopy results show a segment of subepithelial hemorrhage, edema, and erythema from the cecum to the hepatic flexure.

Which of the following is the most appropriate test to perform next?

A. CT angiography
B. Doppler ultrasonography of mesenteric vessels
C. MR angiography
D. Selective catheter angiography

View correct answer for Case 4

Case 5: Next steps in gastrointestinal bleeding

A 72-year-old woman is evaluated after being hospitalized for gastrointestinal bleeding. She went to the emergency department after passing a large amount of bright red blood per rectum at home and became lightheaded. She had a second bloody bowel movement in the emergency department. She is otherwise healthy and takes no medication.

Findings on physical examination, including vital signs, are normal.

Laboratory studies show a hemoglobin level of 9 g/dL (90 g/L).

Which of the following is the most appropriate next step in management?

A. Angiography and arterial embolization
B. Colonoscopy within 8 hours with cleansing enemas
C. Colonoscopy within 24 hours with oral bowel preparation
D. Tagged red blood cell scintigraphy
E. Transfusion of packed red blood cells

View correct answer for Case 5

Answers and commentary

Case 1

Correct answer: A. Colectomy.

This patient requires colectomy. He has a history of ulcerative colitis and presents with fever, tachycardia, hypotension, and a dilated colon on abdominal radiography; the diagnosis is toxic megacolon, a life-threatening condition that complicates approximately 5% of acute, severe cases of ulcerative colitis. Toxic megacolon is defined by the presence of toxicity (fever, tachycardia, hypotension, and leukocytosis) along with evidence of colonic dilation. Patients with this condition have an increased risk for complications such as colonic perforation. Intravenous fluid resuscitation, intravenous high-dose corticosteroids, and broad-spectrum antibiotics (for example, a third-generation cephalosporin with metronidazole) should be initiated in patients with toxic megacolon. Management requires close collaboration with a surgeon; therefore, emergent surgical consultation for consideration of subtotal colectomy is required because of the impending risk for perforation and peritonitis in patients with toxic megacolon. Some patients may respond to medical therapy with high-dose glucocorticoids (in addition to intravenous fluids and broad-spectrum antibiotics), but there should be a low threshold for surgical intervention due to the potential harms associated with toxic megacolon.

Colonoscopy is contraindicated because it would increase the risk for perforation and complications related to toxic megacolon.

CT of the abdomen and pelvis is the optimal imaging modality to evaluate suspected toxic megacolon and may better assess for the presence of colonic necrosis; however, in this case, the diagnosis of toxic megacolon can be confidently made based on the patient's presentation and abdominal radiography, and urgent surgical evaluation is necessary.

Stool studies for enteric pathogens may identify a precipitant of toxic megacolon but require a minimum of 24 hours before test results are received. Surgical consultation should not be delayed to wait for results of stool testing.

Key Point

  • Toxic megacolon is defined by the presence of toxicity and evidence of colonic dilation; it requires prompt surgical treatment.

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Case 2

Correct answer: D. Upper endoscopy.

Upper endoscopy is the most appropriate test to perform next. The patient's presentation is consistent with rapid upper gastrointestinal bleeding (UGIB), likely from an NSAID-induced peptic ulcer. Fifteen percent of patients with presumed lower gastrointestinal bleeding are found to have an upper gastrointestinal source. Factors in this patient that favor a diagnosis of UGIB include young age, hemodynamic instability on presentation, and NSAID use. Approximately 80% of UGIB is due to four causes: peptic ulcer disease, esophagogastric varices, esophagitis, and Mallory-Weiss tear. Bleeding typically stops spontaneously; however, 20% of patients have persistent or recurrent bleeding, which increases mortality. Guidelines recommend upper endoscopy within 24 hours of presentation in patients with features of UGIB.

Angiography is used to diagnose the cause of obscure gastrointestinal bleeding when more common sources are not found on routine upper and lower endoscopy. It is also used for treatment, such as embolization, when a bleeding source has been identified.

Capsule endoscopy employs a wireless capsule camera that is swallowed by the patient to take images of the small bowel. These images are transmitted to a radiofrequency receiver worn by the patient. Capsule endoscopy allows visualization of the entire small bowel. This patient's bleeding is very likely to be accessible by upper endoscopy, the preferred diagnostic test.

Colonoscopy requires bowel preparation for adequate visualization of bleeding sources, and in the setting of acute bleeding with hemodynamic instability, a more urgent diagnostic and therapeutic test is indicated. Colonoscopy would be indicated if the source of bleeding were not identified on upper endoscopy.

Key Point

  • Hematochezia associated with hemodynamic instability in a young patient is likely due to an upper gastrointestinal source.

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Case 3

Correct answer: A. CT scan with contrast.

A CT scan with intravenous contrast is the most appropriate next test for this patient. The patient presents with the classic “herald bleed” of aortoenteric fistula: a brisk bleed associated with hypotension that stops spontaneously and then is followed later by massive gastrointestinal hemorrhage. An aortoenteric fistula is a communication between the aorta and the gastrointestinal tract, most commonly located in the distal duodenum, especially the third portion, because the duodenum is fixed and located just anterior to the aorta. The possibility of an aortoenteric fistula must be considered in a patient with previous aortic graft surgery who presents with gastrointestinal bleeding. It is a life-threatening condition, with a mortality rate of 50% even with surgical intervention. In this setting, the aortoenteric fistula is most commonly due to graft infection, and associated fever and leukocytosis occurs. When there is a high degree of suspicion for aortoenteric fistula, CT with intravenous contrast should be performed before other types of gastrointestinal evaluation because CT can be performed promptly and is noninvasive. CT can reveal evidence of graft infection, such as perigraft soft-tissue thickening or loss of tissue planes, and its reported sensitivity for aortoenteric fistula is 80% or greater.

Mesenteric angiogram can detect bleeding rates as slow as 1 mL/min compared with 0.2 mL/min for tagged red blood cell scintigraphy; however, given the intermittent nature of bleeding from an aortoenteric fistula, mesenteric angiogram and tagged red blood cell scintigraphy are rarely helpful in the diagnosis of this condition.

Upper endoscopy may be performed to rule out other more common sources of bleeding, but in this patient, the presence of fever, leukocytosis, and bleeding points to aortoenteric fistula as the most likely diagnosis, and CT angiogram is the most urgently needed test.

Key Point

  • Gastrointestinal bleeding occurring in patients following aortic graft surgery should raise the possibility of aortoenteric fistula; CT with contrast is the initial test in appropriate patients.

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Case 4

Correct answer: A. CT angiography.

CT angiography is the best next test for this patient, whose clinical presentation with the sudden onset of right-sided, cramping abdominal pain followed by a bloody bowel movement is typical of isolated right-colon ischemia. A CT scan showing thickening of the ascending colon and the colonoscopy features are helpful in confirming this diagnosis. The most common cause of colon ischemia is a nonocclusive low-flow state in the colonic microvasculature. Most cases of colonic ischemia involve the left colon, which is supplied by the inferior mesenteric artery; as with ischemia involving the right colon, the diagnosis is clinical and supported by CT and colonoscopy. Patients with left-sided colonic ischemia tend to heal well with conservative therapy alone, whereas isolated right-colon ischemia can be the harbinger of acute mesenteric ischemia caused by a focal thrombus or embolus of the superior mesenteric artery. This artery supplies both the small intestine and right colon, and the consequences of acute mesenteric ischemia involving the small bowel are severe, with mortality rates that can approach 60%. For this reason, patients with isolated right-colon ischemia require urgent, noninvasive imaging of the mesenteric vasculature to assess the extent of ischemia and nature of the intervention. CT angiography is the recommended method of imaging for diagnosing acute mesenteric ischemia because it can be obtained rapidly. CT angiography visualizes the origins and length of the vessels, characterizes the extent of occlusion, and aids in planning revascularization.

Doppler ultrasonography of the mesenteric vessels is an effective, low-cost tool that can assess the proximal visceral vessels but has limited ability to visualize distal vessels. It is best reserved for the evaluation of patients with chronic mesenteric ischemia, which typically presents with postprandial abdominal pain, sitophobia, and weight loss.

MR angiography provides information about mesenteric arterial flow and avoids the potential harms of radiation and use of contrast that are associated with CT angiography; however, MR angiography takes longer to perform, lacks the required resolution to identify arterial occlusion, and can overestimate the severity of stenosis.

Selective catheter angiography was the standard method for diagnosing mesenteric ischemia; however, it is now used after a revascularization plan has been chosen because CT angiography can be obtained rapidly and is noninvasive.

Key Point

  • Isolated right-colon ischemia may be a warning sign of acute mesenteric ischemia caused by embolism or thrombosis of the superior mesenteric artery and should be evaluated using CT angiography.

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Case 5

Correct answer: C. Colonoscopy within 24 hours with oral bowel preparation.

Colonoscopy within 24 hours with adequate bowel preparation is the most appropriate next step in management. Almost 80% of lower gastrointestinal bleeding (LGIB) is due to diverticulosis, colitis, hemorrhoids, or postpolypectomy bleeding. LGIB typically stops within 24 hours. Colonoscopy is the recommended initial diagnostic test after hemodynamic resuscitation in most patients with significant LGIB. LGIB typically occurs in older individuals and presents as acute bright red blood per rectum or red- or maroon-colored stool (hematochezia). Colonoscopy is able to identify the source of bleeding in two thirds of patients. The American College of Gastroenterology's 2016 guidelines for LGIB recommend oral bowel preparation to increase colonoscopy's diagnostic yield. Randomized controlled trials have not shown a benefit in clinical outcomes or cost with rapid bowel preparation and colonoscopy within 8 to 12 hours compared with a standard oral bowel preparation and colonoscopy within 24 hours for patients with LGIB.

For patients who continue to bleed and have failed endoscopic hemostasis treatments (for example, electrocoagulation, hemoclips, submucosal epinephrine injection), the next therapeutic step is arterial embolization of the bleeding source. Major complications include contrast dye reactions, acute kidney injury, transient ischemic attack, bowel ischemia, hematoma formation, and femoral artery thrombosis. This patient should be evaluated first with colonoscopy before using a more invasive treatment strategy.

Radiographic techniques such as tagged red cell scintigraphy may be useful in evaluating overt gastrointestinal bleeding from an unknown source. Nuclear scans can identify only a general area where bleeding is occurring; they cannot offer accuracy or intervention. Follow-up studies after a positive scan can include repeat endoscopy or angiography; both can offer more accurate localization and therapy. Nuclear scans are often done before angiography.

Transfusion strategies specifically for patients with LGIB have not been developed. Data extrapolated from patients with upper gastrointestinal bleeding found that a restrictive transfusion strategy with a transfusion threshold of hemoglobin less than 7 g/dL (70 g/L) improved survival and decreased rebleeding when compared with a threshold of 9 g/dL (90 g/L). Patients with massive bleeding, acute coronary syndrome, symptomatic peripheral vascular disease, or a history of cerebrovascular disease were excluded from these studies and may benefit from a more lenient transfusion strategy.

Key Point

  • Colonoscopy is the recommended initial diagnostic test after hemodynamic resuscitation in most patients with significant lower gastrointestinal bleeding.