Archive Of Standardized Exam Questions: Pseudomembranous Colitis


This page is dedicated to organizing various examples of standardized exam questions whose answer is pseudomembranous colitis. While this may seem a odd practice, it is useful to see multiple examples of how pseudomembranous colitis will be characterized on standardized exams (namely the boards and the shelf exams). This page is not meant to be used as a tradition question bank (as all of the answers will be the same), however seeing the classic “test” characterization for a disease is quite valuable.


When it comes to standardized exams, each topic has its own “code” marked by key buzzwords, lab findings, clues, etc. If you are well versed in this code you will be able to more quickly identify the condition that is being discussed, and get the right answer on the exam you are taking. Below is the “code” for pseudomembranous colitis

  • Recent antibiotic usage: this is a VERY important component of how this condition will be represented on exams. Patients will have been given antibiotics for various reasons (ear infection etc). 
  • Diarrhea: classically watery diarrhea is present, however blood/mucus may also be noted 
  • Visualized pseudomembranes in the intestines (during colonoscopy/sigmoidoscopy). This makes the diagnosis 
  • Clostridium difficile toxin in the stool will also make the diagnosis. 

Question # 1

A 4 year old boy is borough to the hospital because of a fever, abdominal pain, and diarrhea that contains both blood and mucus. He recently had a recurrent ear infection that was treated with antibiotics. He completed a complete course of amoxicillin-clavulanate 1 ay ago. On exam his temperature is 101.3°F, pulse is 105/min, respiration’s are 18/min, and blood pressure is 105/60 mm Hg. An abdominal exam shows moderate tenderness. There is no rebound tenderness. The rest of the exam is non-contributory. Testing for occult blood is positive. What could be the diagnosis?

Explanation # 1

Diarrhea + recent antibiotic usage = pseudomembranous colitis

Question # 2

A 69 year old woman comes to the clinic because she has been having diarrhea for the past few days. She explained that she has passed 13 watery stools just yesterday. The patients past medical history is notable for a hysterectomy 18 years ago for a bleeding fibroid, and receiving antibiotics 2 weeks ago for a lower lobe pneumonia. She also has a 15 year history of rheumatoid arthritis and underwent a STEMI 6 years ago. She is currently taking both aspirin and prednisone. Her temperature is 102.6°F, pulse is 115/min. respirations are 17/min, and blood pressure is 100/70 mm Hg. A physical exam reveals a lethargic looking woman. Her mucous membranes are dry and an abdominal exam shows slight abdominal distention and right lower quadrant tenderness. Lab studies are collected and shown below:

  • Hemoglobin: 11.9 g/dL
  • Hematocrit: 38%
  • Leukocyte count: 19,000/mm³
  • Platelet count: 340,000/mm³
  • Na+: 150 mEq/L
  • K+: 3.0 mEq/L
  • Bicarbonate: 34 mEq/L

sigmoidoscopy shows the presence of pseudomembranes. What condition does this patient likely have?

Explanation # 2

Diarrhea + recent antibiotic usage + presence of pseudomembranes = pseudomembranous colitis

Question # 3

A hospitalized 40 year old male begins to experience moderate abodminla pain and diarrhea 4 days after undergoing a gastric bypass surgery for obesity He has passed 12 watery stools over the past day. He received prophylactic antibiotics during the procedure, and his initial postoperative course was uncomplicated. His current medications include morphine, propranolol, and omeprazole. The patient’s BMI is 60 kg/m2, temperature is 100.5°F, pulse is 90/min, respirations are 18/min, and blood pressure is 120/75 mm Hg. A physical exam is remarkable for moderate abdominal distention and diffuse abdominal tenderness. The surgical wounds are clean/dry/intact and bowel sounds are normal. A colonoscopy shows multiple areas of patchy white mucosa present on the bowel wall. What might the diagnosis be in this patient?

Explanation # 3

Diarrhea + recent antibiotic usage + presence of pseudomembranes (patchy white mucosa) = pseudomembranous colitis

Question # 4

A 65 year old female comes to the clinic because she has been experiencing watery diarrhea for the past 4 days. She denies seeing any blood or mucus in her stools. She has a history of severe constipation and takes laxatives for this issue. She has not taken any laxatives recently however. Her past medical history is also notable for hypertension, hyperlipidemia, and GERD. She recently had a case of acute sinusitis 3 weeks ago, and finished a course of oral antibiotics. She also takes omeprazole daily for her GERD.  Her temperature is currently 100.5°F. A physical exam reveals an abdomen act is soft with mild distention and slight diffuse tenderness. There is no guarding or rebound tenderness.  What is a possible diagnosis in this patient? 

Watery diarrhea + recent antibiotic usage + usage of omeprazole = pseudomembranous colitis

Explanation # 4

Watery diarrhea + recent antibiotic usage + usage of omeprazole = pseudomembranous colitis

Question # 5

A 25 year old male is recovering from an appendectomy with perforation and periappendicular abscess. He has been receiving Clindamycin and tobramycin for the past week. Early this morning he developed watery diarrhea, and a crampy abdominal pain. He also has a fever and leukocytosis. 

Explanation # 5

Watery diarrhea + recent antibiotic usage = pseudomembranous colitis

Question # 6


Explanation # 6



Many questions on standardized exams go beyond simply recognizing the underlying topic. Often there are specific testable facts regarding some aspect of the topic’s pathophysiology/management/clinical implications that are commonly asked. Some of these are listed below:

  • Organism responsible: Clostridium difficile (C. diff) producing an AB toxin. 
  • What the AB toxin does: 
    • Toxin A is an enterotoxin that binds to the brush border of the gut
    • Toxin B is a cytotoxin that will cause cytoskeletal disruption of cells (via actin depolymerization). This toxin is what causes the pseudomembranous colitis (and ultimately diarrhea)
  • Treatment:


Page Updated: 11.18.2016