DIARRHEA

The differential diagnosis of diarrhea may be approached from either an anatomic or a physiologic basis. The anatomic approach is used in Table 22. In the stomach and duodenum, pernicious anemia and Zollinger–Ellison syndrome are prominent causes. A carcinoma may form a fistula with the transverse colon and cause diarrhea. Viral gastroenteritis, and Giardia infection may also be prominent causes.

DIARRHEA

Liver and biliary tract diseases of all types may cause diarrhea (steatorrhea) by decreasing the secretion of bile. Ampullary carcinoma and cirrhosis are illustrated here, but one should not forget the diarrhea of chronic cholecystitis. The pancreas is the source of important digestive enzymes; as a result, chronic pancreatitis and pancreatic carcinomas may be associated with diarrhea (steatorrhea) in adults, whereas cystic fibrosis should be considered in children. The pancreatic islet cell tumors may secrete gastrin or vasoactive intestinal peptide, causing diarrhea.

Most of the lesions causing diarrhea are in the small intestine. Thus, cholera, Salmonella, Staphylococci, typhoid, and tuberculosis attack here. The carcinoid syndrome, various polyps (especially Peutz–Jeghers), and regional ileitis are also important causes. Toxins and drugs (Table 22) are common causes acting here, as are pellagra and other vitamin deficiencies and food allergies. Systemic autoimmune diseases such as scleroderma and Whipple disease are also important. Mesentery artery insufficiency or obstruction should be considered both here and in the colon.

A wide variety of etiologic agents cause diarrhea by their action on the colon.

1. V—Vascular diseases include ischemic colitis.
2. I—Infectious agents such as bacillary dysentery (Shigella), Escherichia coli, Campylobacter, Yersinia, and amebiasis may ulcerate or inflame the colon.
3. N—Neoplasms such as carcinomas and polyps cause chronic irritation and exudates from the colon with hypermotility and diarrhea.
4. D—Degenerative lesions of the muscularis that cause diverticulosis and allow overgrowth of bacteria and chronic inflammation may lead to diarrhea, but this may be classified under the idiopathic category as well.
5. I—Intoxicating substances, osmotic cathartics, and antibiotics (by allowing overgrowth of bacteria and fungi) may involve the colon (e.g., pseudomembranous colitis). Mucous colitis or irritable bowel syndrome may best be classified as idiopathic.
6. C—Congenital lesions of the colon include the solitary diverticulum of the cecum, malrotation (more frequently associated with intestinal obstruction), and familial polyposis.
7. A—Autoimmune disease of the colon is common and includes both ulcerative colitis and granulomatous colitis.
8. T—Trauma is not a common cause of diarrhea anywhere in the intestinal tract, but certainly surgically induced fistulas may occur in the colon or anywhere else.
9. E—Endocrine disorders do not usually affect the colon directly.

Having considered the local causes of diarrhea, do not forget reflex diarrhea from diseases of other organs, such as pyelonephritis, salpingo-oophoritis, and central nervous system diseases.

Using Table 23, the reader can develop the differential diagnosis of diarrhea with physiology. Diarrhea may result from increased intake of fluids or bulk foods; hyposecretion of enzymes necessary for digestion of food; hypersecretion of gastrointestinal fluids and enzymes; malabsorption of various substances, particularly protein and fat; exudations of pus induced by granulomatous or ulcerative colitis and Salmonella or Shigella infections; hypermobility from stimulation by cathartics, various hormones (e.g., vasoactive intestinal peptides and gastrin), and hypomobility from autonomic dysfunction as occurs in diabetic neuropathy.

Approach to the Diagnosis

Whichever method is applied (anatomic or physiologic), most causes of diarrhea can be recalled before interviewing the patient. Then one can proceed to ask the right questions to eliminate each suspected cause. Combinations of symptoms and signs will assist greatly in narrowing the differential diagnosis. For example, chronic diarrhea and copious mucous without blood suggests irritable bowel syndrome. Chronic diarrhea with mucous and blood suggests ulcerative colitis.

Physical examination is often unrewarding but it may disclose a hepatic, rectal, or pelvic source for the diarrhea; it may also indicate that the diarrhea is a sign of a systemic disease (e.g., scleroderma or hyperthyroidism). Rectal examination may reveal a fecal impaction. A warm stool examination for pus, pH (acid stool suggests lactase deficiency), fat and meat fibers, blood, ova, and parasites is most essential. A stool culture is done. Proctoscopy (immediately if there is blood) followed by colonoscopy, barium enema, and upper gastrointestinal (GI) series is usually necessary in all cases.

Other Useful Tests

1. CBC (malabsorption syndrome)
2. Cathartic stool examination (intestine parasites)
3. Small-bowel series (malabsorption syndrome)
4. Duodenal aspiration (giardiasis, Strongyloides)
5. Lactose tolerance test (lactase deficiency)
6. d-Xylose absorption test (malabsorption syndrome)
7. Serum gastrin (gastrinoma)
8. Urine 5-hydroxyindoleacetic acid (5-HIAA) (malabsorption syndrome, carcinoid tumor)
9. Mucosal biopsy (malabsorption syndrome)
10. Colonoscopy and biopsy (ulcerative colitis, amebic colitis, granulomatous colitis)
11. Stool for Giardia antigen (giardiasis)
12. HIV antibody titer (AIDS)
13. Angiogram (ischemic colitis)
14. Culture for Clostridium difficile (pseudomenbranous colitis)
15. Glucose tolerance test (diabetic enteropathy)

Book Source Details

• Book Title: Differential Diagnosis in Primary Care
• Author(s): R. Douglas Collins
• Year of Publication: 2007
• Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.

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More About This Book: Title: Differential Diagnosis in Primary Care Authors: R. Douglas Collins Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 0-7817-6812-8

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