MKSAP Quiz: 2-year history of abdominal pain, bloating
A 53-year-old man is evaluated for a 2-year history of abdominal pain and bloating, particularly after eating meals, as well as intermittent diarrhea. He underwent Roux-en-Y gastric bypass for weight loss 11 years ago. Following a physical exam and other tests, what is the most likely diagnosis?
A 53-year-old man is evaluated for a 2-year history of abdominal pain and bloating, particularly after eating meals, as well as intermittent diarrhea. He underwent Roux-en-Y gastric bypass for weight loss 11 years ago. He is up to date on assessments for micronutrient deficiencies. He recently regained some weight and was diagnosed with type 2 diabetes mellitus. Medications are semaglutide and vitamin supplements.
Physical examination findings, including vital signs, are normal.
Abdominal radiograph and upper endoscopy findings are normal.
Which of the following is the most likely diagnosis?
A. Clostridioides difficile-associated diarrhea
B. Exocrine pancreatic insufficiency
C. Small intestinal bacterial overgrowth
D. Ulcer at the gastric bypass surgical anastomosis site
MKSAP Answer and Critique
The correct answer is C. Small intestinal bacterial overgrowth. This content is available to ACP MKSAP subscribers in the Gastroenterology and Hepatology section. More information about ACP MKSAP is available online.
The most likely diagnosis is small intestinal bacterial overgrowth (SIBO) (Option C). SIBO represents a syndrome of gastrointestinal symptoms caused by excessive bacteria within the small intestine. Gastric bypass can alter the gastrointestinal microbiome; dysbiosis and SIBO can occur in the setting of anatomic rearrangement of the digestive tract in patients undergoing Roux-en-Y gastric bypass. Common symptoms of SIBO include abdominal discomfort, flatulence, gas, distention, bloating, and diarrhea. Diagnosis requires typical symptoms and a confirmatory test with small-bowel aspirate culture or carbohydrate substrate–based breath testing using glucose or lactulose. However, in patients with a high probability of SIBO and lack of access to objective testing, empiric antibody therapy with subsequent monitoring for symptom relief is a reasonable approach. This patient's history of Roux-en-Y gastric bypass, type 2 diabetes mellitus, and typical SIBO symptoms (including abdominal pain, bloating, and diarrhea) make SIBO the most likely diagnosis.
Clostridioides difficile–associated diarrhea (Option A) usually occurs in settings such as hospitalization or antibiotic exposure, which are not factors in this case. Although community-acquired C. difficile–associated diarrhea can occur, the duration of this patient's symptoms (2 years) argues against this diagnosis. SIBO is a more likely diagnosis in this patient given his risk factors.
Exocrine pancreatic insufficiency (Option B) is unlikely in this patient because gastric bypass should not affect pancreatic function. Additionally, this patient does not have risk factors for pancreatic insufficiency (such as previous/repetitive bouts of acute pancreatitis, alcohol use disorder, calculous gallbladder disease, or congenital malformation).
Ulcers at the gastric bypass anastomosis site (anastomotic ulcers) (Option D) could cause abdominal pain but would not likely explain diarrhea. In addition, this patient's normal upper endoscopy result makes an ulcer less likely.
Key Points
- Common symptoms of small intestinal bacterial overgrowth include abdominal discomfort, flatulence, gas, distention, bloating, and diarrhea.
- Gastric surgery is a risk factor for small intestinal bacterial overgrowth.