A 58-year-old man presents to the clinic with chronic diarrhea and progressive weight loss. Six months ago, he underwent emergency surgery for mesenteric ischemia that required resection of a large portion of his small intestine. Since the surgery, he has experienced 8–10 loose bowel movements daily. He reports fatigue, muscle cramps, and difficulty maintaining his weight despite a normal appetite. His medications include a multivitamin and loperamide as needed. Temperature is 36.7°C (98.1°F), blood pressure is 112/70 mm Hg, pulse is 88/min, and respiratory rate is 14/min. Physical examination demonstrates temporal wasting and mild diffuse abdominal tenderness. Laboratory studies reveal the following:
Hemoglobin: 10.2 g/dL
Albumin: 2.8 g/dL
Calcium: 7.8 mg/dL
Vitamin B12: low
Which of the following is the most likely explanation for this patient’s symptoms?
The correct answer is:
A) Decreased absorptive surface area causing malabsorption
This patient has short bowel syndrome, a malabsorptive disorder that develops after extensive resection of the small intestine. The key clues are the history of major small bowel resection, chronic diarrhea, weight loss, hypoalbuminemia, vitamin B12 deficiency, and multiple nutritional deficiencies. Together, these findings indicate inadequate intestinal absorption rather than an inflammatory or infectious process.
The small intestine is responsible for absorption of most nutrients, vitamins, electrolytes, and fluids. When a substantial portion is removed, the remaining intestine may be unable to absorb sufficient nutrients to maintain normal nutritional status. Patients commonly develop chronic diarrhea because unabsorbed solutes remain in the intestinal lumen, drawing water into the bowel. Weight loss, protein-calorie malnutrition, vitamin deficiencies, electrolyte abnormalities, and dehydration are common consequences.
The specific deficiencies that develop often depend on the location of resection. Terminal ileal resection can cause vitamin B12 deficiency and bile acid malabsorption, while extensive jejunal resection can impair absorption of numerous nutrients. Over time, some intestinal adaptation occurs, but patients with extensive resections frequently require specialized nutritional support.
Management includes dietary modification, antidiarrheal therapy, vitamin and mineral supplementation, and, in severe cases, parenteral nutrition. Step 2 commonly tests the association between terminal ileal resection and vitamin B12 deficiency.
Answer choice B: Excessive bacterial invasion of the colonic mucosa, is incorrect.
This describes an infectious colitis. Such patients typically present with fever, abdominal pain, and inflammatory diarrhea rather than the chronic malabsorptive syndrome seen here.
Answer choice C: Inflammatory destruction of the colonic crypts, is incorrect.
This would be more consistent with inflammatory bowel disease such as ulcerative colitis. Patients usually have bloody diarrhea and evidence of colonic inflammation rather than widespread nutritional deficiencies.
Answer choice D: Pancreatic exocrine insufficiency, is incorrect.
Pancreatic insufficiency can cause malabsorption and weight loss, making it a tempting distractor. However, the history of extensive bowel resection directly explains the patient’s symptoms. Additionally, pancreatic insufficiency would not typically produce vitamin B12 deficiency through loss of absorptive surface area.
Answer choice E: Villous atrophy due to autoimmune enteropathy, is incorrect.
This describes celiac disease. Although celiac disease can cause malabsorption, the temporal relationship to major bowel resection strongly supports short bowel syndrome.
Key Learning Point
Short bowel syndrome results from extensive small intestinal resection and causes chronic diarrhea, malabsorption, weight loss, and nutritional deficiencies due to inadequate absorptive surface area. Terminal ileal resection commonly leads to vitamin B12 deficiency.
