Small intestinal bacterial overgrowth US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Small intestinal bacterial overgrowth. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Small intestinal bacterial overgrowth US Medical PG Question 1: A 25-year-old male presents to his primary care physician for fatigue, abdominal pain, diarrhea, and weight loss. He states that this issue has occurred throughout his life but seems to “flare up” on occasion. He states that his GI pain is relieved with defecation, and his stools are frequent, large, and particularly foul-smelling. The patient has a past medical history of an ACL tear, as well as a car accident that resulted in the patient needing a transfusion and epinephrine to treat transfusion anaphylaxis. His current medications include vitamin D and ibuprofen. He recently returned from a camping trip in the eastern United States. He states that on the trip they cooked packed meats over an open fire and obtained water from local streams. His temperature is 99.5°F (37.5°C), blood pressure is 120/77 mmHg, pulse is 70/min, respirations are 11/min, and oxygen saturation is 98% on room air. Physical exam reveals poor motor control and an ataxic gait on neurologic exam. Cardiac and pulmonary exams are within normal limits. Laboratory studies are ordered and return as below:
Hemoglobin: 9.0 g/dL
Hematocrit: 25%
Haptoglobin: 12 mg/dL
Leukocyte count: 7,500 cells/mm^3 with normal differential
Platelet count: 255,000/mm^3
Serum:
Na+: 140 mEq/L
Cl-: 102 mEq/L
K+: 5.0 mEq/L
HCO3-: 24 mEq/L
BUN: 24 mg/dL
Glucose: 82 mg/dL
Creatinine: 1.0 mg/dL
Ca2+: 9.0 mg/dL
LDH: 457 U/L
AST: 11 U/L
ALT: 11 U/L
Radiography is ordered which reveals a stress fracture in the patient’s left tibia. Which of the following is the best confirmatory test for this patient’s condition?
- A. Stool ELISA
- B. Vitamin B12 and folate level
- C. Vitamin E level (Correct Answer)
- D. Bowel wall biopsy
- E. Iron studies
Small intestinal bacterial overgrowth Explanation: ***Vitamin E level***
- The patient's presentation suggests **celiac disease** causing **malabsorption** with secondary **vitamin E deficiency**, which is causing the specific complications seen here.
- The **neurological findings** of **ataxic gait** and **poor motor control** combined with **hemolytic anemia** (low haptoglobin 12 mg/dL, elevated LDH 457 U/L, anemia) are **pathognomonic for vitamin E deficiency**.
- Vitamin E deficiency causes **spinocerebellar degeneration**, **peripheral neuropathy**, and **hemolytic anemia** due to oxidative damage to RBC membranes and neuronal lipids.
- The **stress fracture** suggests bone disease from calcium/vitamin D malabsorption, but the neuro-hematologic picture is most specific for vitamin E.
- **Serum vitamin E level** is the **confirmatory test** for this specific deficiency syndrome causing the patient's neurological and hematological complications.
- While the underlying condition is likely celiac disease, confirming vitamin E deficiency directly explains the constellation of findings and guides immediate treatment.
*Bowel wall biopsy*
- A **small intestine biopsy** would confirm the underlying diagnosis of **celiac disease** (villous atrophy, crypt hyperplasia) causing the malabsorption.
- However, the question asks for confirmation of "this patient's condition" - referring to the specific syndrome presenting with the characteristic triad of **ataxia + hemolysis + malabsorption**.
- This triad is pathognomonic for **vitamin E deficiency**, making direct measurement more confirmatory for the presenting complication than tissue diagnosis of the underlying cause.
*Vitamin B12 and folate level*
- **Vitamin B12 deficiency** can cause **subacute combined degeneration** with ataxia and neurological symptoms, but typically presents with **posterior column signs** (loss of proprioception, vibration) and **peripheral neuropathy**, not primarily cerebellar ataxia.
- **Folate deficiency** causes **megaloblastic anemia** but does **not** cause neurological deficits or the hemolytic pattern seen here (low haptoglobin, elevated LDH with normal liver enzymes).
- The **hemolytic anemia** is specific to vitamin E deficiency, not B12/folate deficiency.
*Stool ELISA*
- Could detect **Giardia lamblia** given the history of drinking stream water during camping, which can cause acute diarrhea and malabsorption.
- However, this does not explain the **lifelong, recurring symptoms**, **neurological deficits**, **hemolytic anemia**, or **stress fracture**.
- The chronic nature points to a primary malabsorption disorder, not acute infection.
*Iron studies*
- **Iron deficiency** commonly occurs with celiac disease due to duodenal malabsorption and could contribute to the **anemia**.
- However, iron deficiency causes **microcytic anemia**, not hemolytic anemia, and does **not** explain the **low haptoglobin**, **elevated LDH**, **ataxic gait**, or **motor control issues**.
- These findings are specific to vitamin E deficiency.
Small intestinal bacterial overgrowth US Medical PG Question 2: A 21-year-old female presents to her obstetrician because she has stopped getting her period, after being irregular for the last 3 months. Upon further questioning, the patient reveals that she has had a 17 lb. unintended weight loss, endorses chronic diarrhea, abdominal pain, and constipation that waxes and wanes. Family history is notable only for an older brother with Type 1 Diabetes. She is healthy, and is eager to gain back some weight. Her OBGYN refers her to a gastroenterologist, but first sends serology laboratory studies for IgA anti-tissue transglutaminase antibodies (IgA-tTG). These results come back positive at > 10x the upper limit of normal. Which of the following is the gastroenterologist likely to find on endoscopy and duodenal biopsy?
- A. Friable mucosal pseudopolyps with biopsy notable for crypt abscesses
- B. Cobblestoning with biopsy showing transmural inflammation and noncaseating granulomas
- C. Villous atrophy with crypt lengthening and intraepithelial lymphocytes (Correct Answer)
- D. Foamy macrophages, which stain PAS positive
- E. Normal appearing villi and biopsy
Small intestinal bacterial overgrowth Explanation: ***Villous atrophy with crypt lengthening and intraepithelial lymphocytes***
- The patient's symptoms (amenorrhea, weight loss, diarrhea, abdominal pain, constipation) combined with a **positive IgA anti-tissue transglutaminase antibody (IgA-tTG)** strongly suggest **celiac disease**.
- The characteristic endoscopic and histological findings in celiac disease are **villous atrophy**, **crypt hyperplasia (lengthening)**, and increased **intraepithelial lymphocytes** in the small intestine.
*Friable mucosal pseudopolyps with biopsy notable for crypt abscesses*
- This description is characteristic of **ulcerative colitis**, an inflammatory bowel disease, which typically causes **bloody diarrhea** and is not associated with positive IgA-tTG antibodies.
- **Pseudopolyps** result from cycles of ulceration and regeneration, and **crypt abscesses** are hallmarks of active inflammation in ulcerative colitis.
*Cobblestoning with biopsy showing transmural inflammation and noncaseating granulomas*
- This describes the typical findings in **Crohn's disease**, another inflammatory bowel disease, which can cause **abdominal pain** and **diarrhea** but is not linked to IgA-tTG antibodies.
- **Transmural inflammation** means inflammation extends through all layers of the bowel wall, and **noncaseating granulomas** are a key distinguishing feature.
*Foamy macrophages, which stain PAS positive*
- These findings are characteristic of **Whipple's disease**, a rare bacterial infection caused by *Tropheryma whipplei*.
- While Whipple's disease can present with **malabsorption** and **weight loss**, it is not associated with positive celiac serology.
*Normal appearing villi and biopsy*
- Given the patient's strong clinical suspicion for celiac disease and a **highly positive IgA-tTG** test, normal findings on endoscopy and biopsy would be highly unlikely.
- A definitive diagnosis of celiac disease typically requires characteristic histological changes to confirm the serological findings.
Small intestinal bacterial overgrowth US Medical PG Question 3: A 68-year-old man comes to the physician because of headache, fatigue, and nonproductive cough for 1 week. He appears pale. Pulmonary examination shows no abnormalities. Laboratory studies show a hemoglobin concentration of 9.5 g/dL and an elevated serum lactate dehydrogenase concentration. A peripheral blood smear shows normal red blood cells that are clumped together. Results of cold agglutinin titer testing show a 4-fold elevation above normal. An x-ray of the chest shows diffuse, patchy infiltrates bilaterally. Treatment is begun with an antibiotic that is also used to promote gut motility. Which of the following is the primary mechanism of action of this drug?
- A. Inhibition of bacterial RNA polymerase
- B. Inhibition of folic acid synthesis
- C. Free radical creation within bacterial cells
- D. Inhibition of transpeptidase cross-linking at the cell wall
- E. Inhibition of peptide translocation at the 50S ribosomal subunit (Correct Answer)
Small intestinal bacterial overgrowth Explanation: ***Inhibition of peptide translocation at the 50S ribosomal subunit***
- This drug described is likely **erythromycin** or another **macrolide antibiotic**, which inhibits bacterial protein synthesis by binding to the **50S ribosomal subunit** and preventing translocation.
- Macrolides are used to treat **atypical pneumonia** caused by *Mycoplasma pneumoniae*, which is indicated by the patient's symptoms (headache, fatigue, nonproductive cough, bilateral patchy infiltrates) and **cold agglutinin disease**.
*Inhibition of bacterial RNA polymerase*
- This is the mechanism of action of **rifampin**, which is primarily used for **tuberculosis** and **meningitis prophylaxis**, not for atypical pneumonia.
- Rifampin's side effects and spectrum of activity do not align with the implied clinical scenario, especially the gut motility promotion.
*Inhibition of folic acid synthesis*
- This is the mechanism for **sulfonamides** and **trimethoprim**, which are bacteriostatic and target different pathogens than those causing cold agglutinin positive pneumonia.
- These drugs are not known for promoting gut motility.
*Free radical creation within bacterial cells*
- This mechanism is characteristic of **metronidazole**, an antibiotic used for anaerobic bacterial and parasitic infections.
- Metronidazole does not fit the clinical context of atypical pneumonia with cold agglutinins, nor is it a macrolide that promotes gut motility.
*Inhibition of transpeptidase cross-linking at the cell wall*
- This describes the mechanism of **beta-lactam antibiotics** (e.g., penicillins, cephalosporins), which are ineffective against **atypical pneumonia** because *Mycoplasma* lacks a cell wall.
- Beta-lactams do not typically promote gut motility.
Small intestinal bacterial overgrowth US Medical PG Question 4: A 34-year-old man presents with dysphagia. The patient says that he has pain on swallowing which gradually onset 2 weeks ago and has not improved. He denies any change in diet but does say that he recently returned from a prolonged work trip to the Caribbean. No significant past medical history or current medications. On physical examination, the patient looks pale. His tongue is swollen and has a beefy, red appearance. Angular stomatitis is present. Laboratory findings are significant for macrocytic, megaloblastic anemia, decreased serum folate, increased serum homocysteine, and normal methylmalonic acid levels. Which of the following conditions most likely caused this patient’s symptoms?
- A. Diphyllobothrium latum infection
- B. Autoimmune destruction of parietal cells
- C. Tropical sprue (Correct Answer)
- D. Poor diet
- E. Celiac disease
Small intestinal bacterial overgrowth Explanation: ***Tropical sprue***
- The combination of **dysphagia**, **glossitis** (beefy, red, swollen tongue, angular stomatitis), **macrocytic megaloblastic anemia**, **decreased serum folate**, and a history of travel to the **Caribbean** strongly suggests tropical sprue.
- **Normal methylmalonic acid** levels rule out B12 deficiency, leaving folate deficiency as the primary cause of macrocytic anemia, consistent with tropical sprue's malabsorption.
*Diphyllobothrium latum infection*
- This infection causes **vitamin B12 deficiency** due to the parasite absorbing B12, leading to **macrocytic megaloblastic anemia**.
- However, B12 deficiency would present with **elevated methylmalonic acid** (MMA) levels, which are normal in this patient.
*Autoimmune destruction of parietal cells*
- This condition (pernicious anemia) leads to a **lack of intrinsic factor**, causing **vitamin B12 malabsorption** and subsequent B12 deficiency.
- Like *Diphyllobothrium latum* infection, it would also present with **elevated methylmalonic acid** levels.
*Poor diet*
- While a severely poor diet can lead to nutritional deficiencies, the patient denies any change in diet, and the specific constellation of symptoms (especially a history of travel to the Caribbean and **normal MMA**) points more directly to a malabsorption syndrome like tropical sprue.
- While a poor diet could cause folate deficiency, it wouldn't explain the rapid onset of severe symptoms or the specific malabsorptive context without further history.
*Celiac disease*
- Celiac disease typically causes **malabsorption** leading to iron deficiency anemia (microcytic) or, less commonly, folate deficiency (macrocytic).
- However, celiac disease is an immune reaction to **gluten** and is not specifically associated with travel to the Caribbean or the classic oral findings described.
Small intestinal bacterial overgrowth US Medical PG Question 5: A 25-year-old man presents to the physician with 2 days of profuse, watery diarrhea. He denies seeing blood or mucus in the stools. On further questioning, he reveals that he eats a well-balanced diet and generally prepares his meals at home. He remembers having some shellfish from a street vendor 3 days ago. He takes no medications. His past medical history is unremarkable. Which of the following mechanisms most likely accounts for this patient’s illness?
- A. Tyrosine kinase phosphorylation
- B. ADP-ribosylation of Gs protein (Correct Answer)
- C. Tyrosine kinase dephosphorylation
- D. Osmotic effect of intestinal contents
- E. Inflammation of the gastrointestinal wall
Small intestinal bacterial overgrowth Explanation: ***ADP-ribosylation of Gs protein***
- The patient's history of consuming **shellfish from a street vendor** and presenting with **profuse, watery diarrhea** strongly suggests **cholera**.
- **Cholera toxin** works by irreversibly ADP-ribosylating the **Gs alpha subunit**, leading to constitutive activation of **adenylate cyclase** and increased intracellular **cAMP**, which causes excessive fluid and electrolyte secretion into the intestinal lumen.
*Tyrosine kinase phosphorylation*
- This mechanism is characteristic of signaling pathways involved in growth and differentiation, often seen with **growth factor receptors**, and is not the primary cause of acute, watery diarrhea from food poisoning.
- While some bacterial toxins can affect intracellular signaling, **tyrosine kinase phosphorylation** is not the direct mechanism for the massive fluid loss seen in cholera.
*Tyrosine kinase dephosphorylation*
- This process typically downregulates cell signaling pathways, which would likely **decrease** cellular activity, rather than trigger the profuse secretion seen in this patient's presentation.
- It is not a known mechanism for the pathogenesis of infectious diarrheal diseases such as cholera.
*Osmotic effect of intestinal contents*
- While **osmotic diarrhea** is characterized by the presence of non-absorbable solutes in the gut lumen, drawing water in, the history here points more to an actively secreted fluid loss.
- The sheer volume and rapid onset of the diarrhea suggest an active secretory mechanism rather than simply an osmotic effect from malabsorption.
*Inflammation of the gastrointestinal wall*
- **Inflammatory diarrhea** typically involves blood or mucus in the stool, fever, and abdominal pain, none of which are reported by the patient.
- The patient's "profuse, watery" diarrhea without blood or mucus signifies a non-inflammatory, secretory etiology often caused by toxins.
Small intestinal bacterial overgrowth US Medical PG Question 6: A 51-year-old gentleman presents with new onset bilateral paresthesias of his feet. He also admits that he has not been able to exercise as much as previously and his friends have commented that he looks pale. Upon physical exam you find that he has conjunctival pallor and mildly decreased sensation and proprioception on his feet bilaterally. Based on your suspicions you decide to obtain a blood smear where you see megaloblasts as well as hypersegmented neutrophils. Given these findings you decide to investigate the cause of his disorder by injecting an intramuscular vitamin, then feeding him a radiolabeled version of the same vitamin orally. After waiting 24 hours you see that no radiolabeled vitamin appears in the urine so you repeat the test with intrinsic factor added to the oral mixture, at which point 20% of the radiolabeled vitamin appears in the urine. Which of the following is the most likely etiology of this gentleman's symptoms?
- A. Bacterial overgrowth
- B. Pancreatic insufficiency
- C. Insufficient vitamin intake
- D. Pernicious anemia (Correct Answer)
- E. Folate deficiency
Small intestinal bacterial overgrowth Explanation: ***Pernicious anemia***
- The combination of **neurological symptoms** (paresthesias, decreased proprioception), **anemia symptoms** (pallor, fatigue), **megaloblastic anemia** on blood smear (megaloblasts, hypersegmented neutrophils), and the specific Schilling test results (vitamin B12 malabsorption corrected by added **intrinsic factor**) is diagnostic for pernicious anemia.
- Pernicious anemia is an autoimmune condition targeting **gastric parietal cells** or **intrinsic factor** itself, leading to **vitamin B12 deficiency** due to impaired absorption.
*Bacterial overgrowth*
- **Bacterial overgrowth in the small intestine** can consume vitamin B12, leading to deficiency, but the Schilling test would show improvement with **antibiotics**, not intrinsic factor.
- While it can cause B12 deficiency and megaloblastic anemia, improvement upon adding intrinsic factor points away from this diagnosis.
*Pancreatic insufficiency*
- **Pancreatic enzymes** are required to cleave vitamin B12 from its binding proteins, but the **Schilling test** would show improvement with **pancreatic enzyme supplements**, not intrinsic factor.
- While pancreatic insufficiency can lead to B12 malabsorption, the specific Schillings test results rule it out.
*Insufficient vitamin intake*
- **Insufficient dietary intake** of vitamin B12 would lead to B12 deficiency, but in such a case, the **Schilling test** would show normal absorption of radiolabeled B12 even without intrinsic factor in the second stage.
- The initial B12 malabsorption indicates an absorption problem, not solely a dietary lack.
*Folate deficiency*
- **Folate deficiency** also causes **megaloblastic anemia** and can present with fatigue and pallor, but it does **not cause neurological symptoms** like paresthesias or proprioception deficits.
- The Schilling test specifically evaluates **vitamin B12 absorption**, not folate levels, so it would be irrelevant for diagnosing pure folate deficiency.
Small intestinal bacterial overgrowth US Medical PG Question 7: A 55-year-old man presents to the physician with complaints of 5 days of watery diarrhea, fever, and bloating. He has not noticed any blood in his stool. He states that his diet has not changed recently, and his family has been spared from diarrhea symptoms despite eating the same foods that he has been cooking at home. He has no history of recent travel outside the United States. His only medication is high-dose omeprazole, which he has been taking daily for the past few months to alleviate his gastroesophageal reflux disease (GERD). Which of the following is the most appropriate initial test to work up this patient’s symptoms?
- A. Stool toxin assay (Correct Answer)
- B. Colonoscopy
- C. Fecal occult blood test
- D. Stool culture
- E. Stool ova and parasite
Small intestinal bacterial overgrowth Explanation: ***Stool toxin assay***
- The patient's presentation of **watery diarrhea** and fever, especially with a history of **high-dose omeprazole use**, strongly suggests **Clostridioides difficile infection**.
- **Omeprazole** (a proton pump inhibitor) reduces stomach acid, which can disrupt the normal gut flora and increase susceptibility to *C. difficile*; a **stool toxin assay** is the most direct diagnostic test for this infection.
*Colonoscopy*
- While a colonoscopy can visualize pseudomembranes associated with severe *C. difficile* colitis, it is an **invasive procedure** and not the initial diagnostic test of choice for suspected infectious diarrhea.
- It is usually reserved for cases with atypical presentations, suspected complications, or when other diagnostic tests are inconclusive.
*Fecal occult blood test*
- The patient describes **watery diarrhea** and specifically states he has **not noticed any blood in his stool**, making a fecal occult blood test unlikely to be helpful in this acute setting.
- This test is primarily used for screening **colorectal cancer** or identifying chronic gastrointestinal bleeding.
*Stool culture*
- A stool culture primarily identifies bacterial pathogens like *Salmonella*, *Shigella*, or *Campylobacter*, which typically cause diarrheal illnesses that may include **bloody stools** or have specific epidemiological links (e.g., foodborne outbreaks).
- Given the history of **omeprazole use** and the absence of blood, *C. difficile* is more likely than these common bacterial enteritides, and a stool culture does not detect *C. difficile* itself.
*Stool ova and parasite*
- This test is used to detect **parasitic infections** (e.g., Giardia, Cryptosporidium), which can cause watery diarrhea and bloating.
- However, given the specific risk factor of **omeprazole use**, **Clostridioides difficile** infection is a more probable diagnosis, making the stool toxin assay the more appropriate initial test.
Small intestinal bacterial overgrowth US Medical PG Question 8: A 34-year-old woman comes to the emergency department because of decreased appetite, nausea, vomiting, and episodic abdominal pain for the past two months. The pain is sharp, colicky, and lasts about an hour after meals. Her stools are light in appearance and difficult to flush. Physical examination shows tenderness in the right upper quadrant. Without treatment, this patient is at greatest risk for developing which of the following?
- A. Steatohepatitis
- B. Megaloblastic anemia
- C. Delayed wound healing
- D. Low bone mineral density (Correct Answer)
- E. Glossitis
Small intestinal bacterial overgrowth Explanation: ***Low bone mineral density***
- This patient presents with symptoms highly suggestive of **gallstones** (cholelithiasis) leading to **biliary obstruction** or **cholestasis**, evidenced by episodic postprandial colicky pain, nausea, vomiting, and light-colored, difficult-to-flush stools (steatorrhea due to **fat malabsorption**).
- Chronic fat malabsorption inhibits the absorption of **fat-soluble vitamins** (A, D, E, K). A deficiency in **vitamin D** is a significant risk factor for **low bone mineral density** and **osteoporosis** over time.
*Steatohepatitis*
- **Steatohepatitis** (fatty liver inflammation) is typically associated with **metabolic syndrome**, chronic alcohol use, or rapid weight loss, which are not directly indicated here.
- While gallstones can be linked to obesity, they do not directly cause steatohepatitis in the way described by the patient's acute symptoms.
*Megaloblastic anemia*
- **Megaloblastic anemia** is primarily caused by deficiencies in **vitamin B12** or **folate**.
- While malabsorption can lead to B12 deficiency (e.g., in pancreatic insufficiency affecting intrinsic factor activity), biliary obstruction directly impacts fat-soluble vitamin absorption, not primarily B12 or folate.
*Delayed wound healing*
- **Delayed wound healing** can be a symptom of **vitamin C** or **zinc deficiency**, or overall malnutrition.
- Although chronic malabsorption can lead to general malnutrition, vitamin D deficiency and its impact on bone health are a more specific and immediate long-term risk associated with the described symptoms.
*Glossitis*
- **Glossitis** (inflammation of the tongue) is typically associated with deficiencies in **vitamin B group** vitamins (e.g., B12, folate, niacin, riboflavin) or **iron deficiency**.
- While this patient might eventually develop general nutritional deficiencies, biliary obstruction leading to fat malabsorption does not directly or primarily cause these specific B vitamin deficiencies.
Small intestinal bacterial overgrowth US Medical PG Question 9: A 63-year-old woman comes to the physician because of diarrhea and weakness after her meals for 2 weeks. She has the urge to defecate 15–20 minutes after a meal and has 3–6 bowel movements a day. She also has palpitations, sweating, and needs to lie down soon after eating. One month ago, she underwent a distal gastrectomy for gastric cancer. She had post-operative pneumonia, which was treated with cefotaxime. She returned from a vacation to Brazil 6 weeks ago. Her immunizations are up-to-date. She is 165 cm (5 ft 5 in) tall and weighs 51 kg (112 lb); BMI is 18.6 kg/m2. Vital signs are within normal limits. Examination shows a well-healed abdominal midline surgical scar. The abdomen is soft and nontender. Bowel sounds are hyperactive. Rectal examination is unremarkable. Which of the following is the most appropriate next step in management?
- A. Dietary modifications (Correct Answer)
- B. Stool PCR test
- C. Octreotide therapy
- D. Metronidazole therapy
- E. Stool microscopy
Small intestinal bacterial overgrowth Explanation: ***Dietary modifications***
- This patient's symptoms (diarrhea, weakness, palpitations, sweating, and urge to defecate soon after meals) following a **distal gastrectomy** are classic for **dumping syndrome**. **Dietary modification** is the first-line treatment.
- Recommended modifications include **smaller, more frequent meals**, avoiding high-sugar foods, increasing protein and fiber, and separating solids from liquids during meals.
*Stool PCR test*
- While diarrhea is present, the patient's symptoms are strongly linked to her recent gastrectomy and meal ingestion rather than an infectious cause.
- A stool PCR test would be appropriate if there were other signs of infection, such as fever or severe abdominal pain, or if dietary modifications failed to resolve symptoms.
*Octreotide therapy*
- **Octreotide**, a somatostatin analog, is reserved for **severe cases of dumping syndrome** that do not respond to dietary modifications.
- It works by inhibiting the release of gastrointestinal hormones and slowing gastric emptying, but it is not the initial management step.
*Metronidazole therapy*
- **Metronidazole** is an antibiotic used to treat bacterial and parasitic infections. There is no evidence suggesting an infection in this patient.
- The timing of symptoms immediately post-meal points away from an infection and towards post-gastrectomy complications.
*Stool microscopy*
- Similar to a stool PCR, **stool microscopy** is used to identify parasites or other pathogens.
- Given the classic presentation of dumping syndrome following gastrectomy, an infectious cause is less likely, and other diagnostic tests should be pursued if dietary measures fail.
Small intestinal bacterial overgrowth US Medical PG Question 10: A 58-year-old female, being treated on the medical floor for community-acquired pneumonia with levofloxacin, develops watery diarrhea. She reports at least 9 episodes of diarrhea within the last two days, with lower abdominal discomfort and cramping. Her temperature is 98.6° F (37° C), respiratory rate is 15/min, pulse is 67/min, and blood pressure is 122/98 mm Hg. Her physical examination is unremarkable. Laboratory testing shows:
Hb% 13 gm/dL
Total count (WBC): 13,400/mm3
Differential count:
Neutrophils: 80%
Lymphocytes: 15%
Monocytes: 5%
ESR: 33 mm/hr
What is the most likely diagnosis?
- A. Ulcerative colitis
- B. C. difficile colitis (Correct Answer)
- C. Osmotic diarrhea
- D. Giardiasis
- E. Irritable bowel syndrome
Small intestinal bacterial overgrowth Explanation: ***C. difficile colitis***
- The patient's recent **antibiotic use (levofloxacin)**, followed by the development of **watery diarrhea** (9 episodes in 2 days) with abdominal cramping, is highly suggestive of *Clostridioides difficile* infection.
- The elevated **WBC count (13,400/mm3)** and **ESR (33 mm/hr)** indicate an inflammatory response, which is common in *C. difficile* colitis.
*Ulcerative colitis*
- Ulcerative colitis typically presents with **bloody diarrhea**, abdominal pain, and tenesmus, usually with a more chronic or relapsing course, which is not described.
- While it can manifest with flares, the direct temporal relationship with **antibiotic use** and the lack of bloody stools make it less likely.
*Osmotic diarrhea*
- Osmotic diarrhea is often related to the ingestion of **non-absorbable substances** (e.g., lactulose, sorbitol) or malabsorption and generally resolves with fasting.
- It is not typically associated with a significant **inflammatory response** (elevated WBC, ESR) or a clear link to recent antibiotic use.
*Giardiasis*
- Giardiasis is a parasitic infection that causes **protozoal diarrhea**, often characterized by foul-smelling, fatty stools, flatulence, and abdominal cramps.
- It is usually acquired from contaminated water and typically doesn't follow **antibiotic therapy** in this manner.
*Irritable bowel syndrome*
- IBS is a functional gastrointestinal disorder characterized by **chronic abdominal pain** and altered bowel habits (diarrhea, constipation, or both) in the absence of structural or biochemical abnormalities.
- It does not present as an acute, severe diarrheal illness linked to **antibiotic use** with systemic inflammatory markers.
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