Differentials
Infectious gastroenteritis
SIGNS / SYMPTOMS
Recent travel or exposure. Often acute, may be associated with fever or other systemic symptoms.
INVESTIGATIONS
Microscopic examination of the stool for ova and parasites: may isolate specific ova and/or parasites, including Giardia and Entamoeba histolytica.
Osmotic diarrhea
SIGNS / SYMPTOMS
Symptoms resolve with fasting.
INVESTIGATIONS
Contrast-enhanced intestinal radiographs: helps differentiate from intestinal hypermotility and inflammatory bowel disease.
Biopsy rules out infectious causes as well as inflammatory bowel disease.
Ileal bile acid malabsorption
SIGNS / SYMPTOMS
Lower volume of stool output. Symptoms resolve with fasting.
INVESTIGATIONS
Cholestyramine trial: binding of excess bile salts reduces the diarrhea that is typically a symptom of excess bile reaching the colon.
Gastrinoma
SIGNS / SYMPTOMS
Acidic diarrhea, increased gastric acid production, gastroesophageal reflux disease, pain/peptic ulcer disease, absence of metabolic acidosis.
INVESTIGATIONS
Serum gastrin levels: elevated.
Carcinoid syndrome
SIGNS / SYMPTOMS
More severe flushing.
INVESTIGATIONS
24-hour urinary 5-hydroxyindoleacetic acid: elevated.
Somatostatinoma
SIGNS / SYMPTOMS
Steatorrhea, diabetes mellitus, gallstones.
INVESTIGATIONS
Plasma somatostatin levels: elevated.
Crohn disease
SIGNS / SYMPTOMS
Less severe diarrhea and associated abdominal pain. Perianal lesions, mouth ulceration, blood in stools.
INVESTIGATIONS
Plain film abdominal radiograph: small-bowel or colonic dilatation, calcification, sacroiliitis, and/or intra-abdominal abscesses.
Colonoscopy: aphthous ulcers, hyperemia, edema, cobblestoning, and/or skip lesions.
Biopsy: transmural involvement with noncaseating granulomas.
Ulcerative colitis
SIGNS / SYMPTOMS
Less severe diarrhea and associated abdominal pain. Rectal bleeding, blood in stools, arthritis, spondylitis, skin rash, uveitis, episcleritis.
INVESTIGATIONS
Plain film abdominal radiograph: ulcerated colon usually contains no solid feces, dilated loops with air-fluid level secondary to ileus.
Colonoscopy and flexible sigmoidoscopy: continuous uniform rectal involvement, loss of vascular marking, diffuse erythema, mucosal granularity, fistulas, and/or mild "backwash" ileitis in pancolitis.
Biopsy: continuous distal disease, mucin depletion, basal plasmacytosis, diffuse mucosal atrophy, absence of granulomata, and anal sparing.
Irritable bowel syndrome (IBS)
SIGNS / SYMPTOMS
Often presents with intermittent and chronic history of diarrhea. Less severe diarrhea and associated abdominal pain.
INVESTIGATIONS
No specific diagnostic test; symptoms and age guide initial workup to exclude non-IBS disease.
Celiac disease
SIGNS / SYMPTOMS
Diarrhea and evidence of malabsorption are typical.
INVESTIGATIONS
Immunoglobulin A-tissue transglutaminase (IgA-tTG) or IgG DGP (deamidated gliadin peptide): elevated titer.
Endoscopy with duodenal biopsy: atrophy and scalloping of mucosal folds, nodularity and mosaic pattern of mucosa, typical histologic findings (presence of intraepithelial lymphocytes, villous atrophy, and crypt hyperplasia).
Small intestinal bacterial overgrowth
SIGNS / SYMPTOMS
History of diabetes, past surgery, celiac or Crohn disease; typical symptoms are bloating, wind, flatulence, cramping, and mild to moderate diarrhea.
Exam is generally nonspecific.
INVESTIGATIONS
Breath test: rise of >20 ppm of hydrogen or methane (or both) within 90 minutes.
Therapeutic trial of antibiotics: significant and lasting improvement of symptoms.
Colon carcinoma
SIGNS / SYMPTOMS
Less severe diarrhea and improvement with fasting. Rectal bleeding, positive family history, anemia.
INVESTIGATIONS
Quantitative fecal immunochemical test: ≥10 micrograms of hemoglobin/g of feces.
Colonoscopy: ulcerating exophytic mucosal lesion that may narrow the bowel lumen.
Biopsy: characteristic pathologic appearances and degree of tumor differentiation.
Drug effects
SIGNS / SYMPTOMS
Long-term laxative abuse; other diarrhea-causing drugs (e.g., proton-pump inhibitors, nonsteroidal anti-inflammatory drugs, metformin, quinine); in many cases, patients on multiple drugs; time of onset can be very variable, so can be difficult to pinpoint offending agent.
INVESTIGATIONS
Improvement in symptoms upon discontinuation of drug.
Hyperthyroidism
SIGNS / SYMPTOMS
Less severe diarrhea. Palpitations, menstrual irregularity, tremor, anxiety, diaphoresis, exophthalmos.
INVESTIGATIONS
Thyroid function testing: reduced thyroid-stimulating hormone, elevated triiodothyronine, and elevated thyroxine.
Addison disease
SIGNS / SYMPTOMS
Systemic collapse, hyperpigmentation, salt craving.
INVESTIGATIONS
Serum electrolyte levels: reduced serum sodium, reduced serum calcium, elevated potassium.
Adrenocorticotropic hormone level: elevated.
Medullary cancer of the thyroid
SIGNS / SYMPTOMS
Neck mass, family history of multiple endocrine neoplasia type 2A or 2B.
INVESTIGATIONS
Serum calcitonin levels: may be elevated.
Biopsy: characteristic pathologic appearances.
Pheochromocytoma
SIGNS / SYMPTOMS
Hypertension, palpitations, diaphoresis.
INVESTIGATIONS
Urinary or serum catecholamine, metanephrine, normetanephrine levels: elevated.
Neuroblastoma
SIGNS / SYMPTOMS
Rarely occurs over the age of 10 years.
INVESTIGATIONS
Serum and/or urinary catecholamine levels: may be elevated.
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