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PATIENT
Mr. C is a 35-year-old man who comes to your outpatient office complaining of 1 day of diarrhea.
What is the differential diagnosis of diarrhea? How would you frame the differential?
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CONSTRUCTING A DIFFERENTIAL DIAGNOSIS
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Clinically, it is probably most useful to define acute diarrhea as diarrhea (bowel movements of a looser consistency than usual that occur more than 3 times a day) that develops over a period of 1–2 days and lasts for less than 4 weeks. The differential diagnosis below uses pivotal points in a patient’s presenting symptoms to organize potential diagnoses into 3 categories: noninfectious, gastroenteritis, and infectious colitis. Noninfectious diarrhea is recognized by the lack of constitutional symptoms. Infectious diarrhea that presents with large volume (often watery) stool, constitutional symptoms, nausea and vomiting, and often abdominal cramps can be categorized as gastroenteritis. Infectious colitis presents with fever, tenesmus, and dysentery (stools with blood and mucus). This structure is easy to remember, focuses history taking, allows prognosticating, and is also a good framework on which to consider therapy. Figure 13-1 uses this framework to suggest therapy.
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Noninfectious diarrhea
Medications and other ingestible substances (some with osmotic effect)
Sorbitol (gum, mints, pill fillers)
Mannitol
Fructose (fruits, soft drinks)
Fiber (bran, fruits, vegetables)
Lactulose
Magnesium-containing medications
Nutritional supplements
Antacids
Laxatives
Malabsorption
Lactose intolerance
Pancreatitis
Medications causing diarrhea through nonosmotic means
Metformin
Antibiotics
Colchicine
Digoxin
Selective serotonin reuptake inhibitor antidepressants
Infectious diarrhea: gastroenteritis
Viral (most common)
Caliciviruses (including Norovirus)
Rotovirus
Bacterial
Vibrio cholera
Escherichia coli
Shigella species
Salmonella species
Campylobacter species
Yersinia enterocolitica
Toxin-mediated
Staphylococcus aureus
Clostridium perfringens
Bacillus cereus
Infectious diarrhea: inflammatory colitis
Shigella species
E coli
Campylobacter species
Salmonella species
Y enterocolitica
Clostridium difficile
Klebsiella oxytoca
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The first symptom the patient noted was loss of appetite while eating breakfast. He was unable to finish his usual cup of coffee and a bowl of cereal. During his 20-minute drive to work he developed nausea and diaphoresis. Upon arriving at work he developed low-grade fever, abdominal cramping, and vomiting. Over the next 12 hours, diarrhea developed. He describes the stool being watery and brown without any blood.
At this point, what is the leading hypothesis, what are the active alternatives, and is there a must not miss diagnosis? Given this differential diagnosis, what tests should be ordered?
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RANKING THE DIFFERENTIAL DIAGNOSIS
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The pivotal point in this case presentation is the acute onset of watery diarrhea. The early predominance of nausea will also help in making a diagnosis. This presentation certainly speaks for an infectious cause. The low-grade fever and absence of dysentery make it likely that the diagnosis is in the category of gastroenteritis. Table 13-1 lists the differential diagnosis.
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