Review Question - QID 218535

This patient with a history of Roux-en-Y gastric bypass presenting with chronic abdominal bloating, discomfort, watery diarrhea without steatorrhea, flatulence, a benign abdominal exam, and macrocytic anemia suggestive of vitamin B12 deficiency has small intestinal bacterial overgrowth (SIBO). SIBO is characterized by the unregulated growth of bacteria within the small bowel, leading to malabsorption.

SIBO is classically seen post-surgically after the creation of a blind loop of bowel (e.g., in Roux-en-Y procedures), but can also be found in patients with intestinal motility disorders such as irritable bowel syndrome or patients with chronic pancreatitis, which alters the intestinal chemical environment. Patients with SIBO present with bloating, abdominal discomfort, and chronic watery diarrhea. Steatorrhea is rare. By destruction of the absorptive interface, SIBO results in malabsorption, which can present with signs of vitamin deficiency. For example, patients with vitamin B12 deficiency can present with megaloblastic anemia, neuropsychiatric changes, and neuropathy. Patients with vitamin B1 deficiency can present with Wernicke encephalopathy, characterized by the triad of gait ataxia, ophthalmoplegia, and altered mental status. Diagnosis of SIBO can be secured with the carbohydrate breath test. Treatment is with rifaximin for 14 days. Alternate regimens include trimethoprim-sulfamethoxazole, ciprofloxacin, metronidazole, or amoxicillin-clavulanic acid.

Sachdeva et al. studied the frequency and predictors of SIBO in patients with irritable bowel syndrome. They found that diarrhea-predominant irritable bowel syndrome, female sex, and bloating were predictive of SIBO in these patients. They recommended that clinicians identify these risk factors in patients with irritable bowel syndrome, which could lead to the diagnosis of underlying SIBO.

Incorrect Answers:
Answer 1: Direct ingestion of a preformed toxin is the cause of food poisoning. These toxins are preformed by Staphylococcus aureus or Bacillus cereus. Patients with food poisoning present with vomiting as the predominant symptom, although watery diarrhea can also be present. The onset of symptoms is almost always within 6 hours, and as early as within 30 minutes, of ingestion of the food.

Answer 2: Infection with a strain of bacteria that produces heat-stable toxins is the cause of travelers’ diarrhea, which is caused by infection with enterotoxigenic strains of Escherichia coli. Patients with travelers’ diarrhea present with watery diarrhea that may turn bloody, nausea, vomiting, and fever within 10 days of returning from an endemic area. Symptoms are typically self-limited and resolve within 1-5 days.

Answer 3: Ingestion of a parasite causing chronic malabsorption is the cause of giardiasis. Giardiasis is caused by ingestion of water contaminated with Giardia cysts. Patients with giardiasis present with chronic steatorrhea, weight loss, and malabsorption. In contrast, this patient does not have steatorrhea, making this less likely.

Answer 5: Viral destruction of enterocytes refers to rotavirus infection. Adults with rotavirus infection present with mild nausea, vomiting, watery diarrhea, and fever. While this patient was exposed to schoolchildren with a likely viral gastroenteritis syndrome, her chronic watery diarrhea predates this exposure. Additionally, malabsorption would not be expected.

Bullet Summary:
Small intestinal bacterial overgrowth presents with bloating, abdominal discomfort, and chronic watery diarrhea in patients with predisposing conditions (e.g., irritable bowel syndrome, gastrointestinal surgery that created a blind loop) and is treated with rifaximin.