Differentials
Crohn disease
SIGNS / SYMPTOMS
May present with fatigue, diarrhea, abdominal pain, weight loss, fever and rectal bleeding.
Other signs may include oral ulcers, perianal skin tags, fistulae, abscesses and sinus tracts; abdominal exam may reveal a palpable mass in the ileocecal area; no mass present on digital rectal examination.
INVESTIGATIONS
Stool culture, microscopy and antigen testing: negative.
Fecal occult blood: positive.
Upper gastrointestinal and small bowel series: edema and ulceration of the mucosa with luminal narrowing and strictures.
CT/MRI abdomen: skip lesions, bowel wall thickening, surrounding inflammation, abscess, fistulae.
Colonoscopy: aphthous ulcers, hyperemia, edema, cobblestoning, skip lesions.
Ulcerative colitis
SIGNS / SYMPTOMS
May present with bloody diarrhea, history of lower abdominal pain, fecal urgency, presence of extraintestinal manifestations (e.g., erythema nodosum, acute arthropathy), history of primary sclerosing cholangitis. No mass present on digital rectal exam.
INVESTIGATIONS
Stool culture, microscopy and antigen testing: negative.
Histology: continuous distal disease, mucin depletion, basal plasmacytosis, diffuse mucosal atrophy, absence of granulomata and anal sparing.
Colonoscopy: rectal involvement, continuous uniform involvement, loss of vascular marking, diffuse erythema, mucosal granularity, normal terminal ileum (or mild "backwash" ileitis in pancolitis).
Microscopic colitis
SIGNS / SYMPTOMS
Chronic watery, non-bloody diarrhea.
Other common symptoms include fecal urgency, fecal incontinence, and nocturnal stools.
More common in patients >50 years and female.
INVESTIGATIONS
Ileocolonoscopy with biopsies from the right and left colon: confirms diagnosis.[48] Colonic mucosa has a normal or near-normal gross appearance.
Biopsy: demonstrates collagenous colitis (i.e., thickened subepithelial collagenous band of ≥10 micrometer (normal <5 micrometer) or lymphocytic colitis (i.e., increased number of intraepithelial lymphocytes of ≥20 per 100 surface epithelial cells (normal <5 micrometer). Both types show an increased inflammatory infiltrate in the lamina propria.[48]
Celiac disease
SIGNS / SYMPTOMS
Patients with celiac disease usually have weight loss. The physical exam is usually normal. Some patients with celiac disease will have early osteoporosis.
INVESTIGATIONS
Basic laboratory tests: may show iron-deficiency anemia, hypocalcemia, or a prolonged prothrombin time, although many patients with celiac disease will have no routine laboratory abnormalities.
Anti-tissue transglutaminase antibodies may be detected in celiac disease.[44] Small bowel biopsy will be abnormal with partial villous atrophy in celiac disease.
Colon cancer
SIGNS / SYMPTOMS
Colon cancer can sometimes cause a change in bowel habits with either constipation or more frequent, smaller caliber stools. Some, but not all, colon cancer patients will have blood in their stool, and a rectal cancer may be palpable on rectal exam.
INVESTIGATIONS
CBC: iron-deficiency anemia may be present.
Fecal occult blood: may be positive.
Quantitative fecal immunochemical test (FIT): The UK guidelines recommend urgent referral to secondary care for FIT value of ≥10 micrograms of hemoglobin/g of feces.[37][38]
Endoscopy: will demonstrate malignant growth; colon cancer can be diagnosed by colonoscopy, whereas cancers of the rectum, sigmoid, and lower descending colon can be seen with flexible sigmoidoscopy.
Barium enema: although less sensitive than endoscopy, many colon cancers can be seen on air-contrast barium enema.
CT colonography is an option for screening for colorectal cancer.
Bowel infections
SIGNS / SYMPTOMS
Most bacterial and viral infections in immunocompetent patients are acute. The parasite Giardia can be associated with diarrhea, nausea, and bloating. Giardiasis may also cause steatorrhea.
INVESTIGATIONS
Stool exam positive for ova and parasites or stool antigen detection positive for G lamblia can be used for screening. Multiple stools should be examined.
Nonceliac gluten sensitivity
SIGNS / SYMPTOMS
Patients will have bloating, abdominal cramping, and diarrhea similar to IBS.
INVESTIGATIONS
Studies will be negative, including tissue transglutaminase antibody.
There is no biomarker.
Patient's symptoms improve on gluten-free diet, especially without wheat.[49]
Bile acid malabsorption
SIGNS / SYMPTOMS
Patients have persistent diarrhea. May be clinically indistinguishable from diarrhea-predominant IBS (IBS-D). More than 25% of patients who meet the diagnostic criteria for IBS-D have bile acid malabsorption.[30]
INVESTIGATIONS
Test result indicating bile acid malabsorption: elevated fecal bile acids on 48-hour stool collection; reduced serum fibroblast growth factor 19; <15% retained 23‐seleno‐25‐homotaurocholic acid (SeHCAT) 1 week after ingestion.
Symptoms improve with an empiric trial of bile acid binder.
Small bowel bacterial overgrowth
SIGNS / SYMPTOMS
Patients present with abdominal bloating, diarrhea, and abdominal cramps. History may show conditions that alter intestinal anatomy, motility, and gastric acid secretion (e.g., use of proton pump inhibitors or anatomical disturbances in the bowel, including fistulae, diverticula, and blind loops created after surgery).[50]
INVESTIGATIONS
Hydrogen breath testing indicates bacterial overgrowth.
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