Differential tests

There are many conditions that produce a chronic diarrhea, which must be differentiated from the relatively common types that last only a few days and usually respond to ordinary treatment. Diarrhea in infants will not be specifically discussed, since this is a special problem peculiar to that age group.

In patients of all ages with long-term or chronic diarrhea, a stool should be obtained for culture to rule out the presence of Salmonella or Shigella bacteria. In some areas, Campylobacter or Yersinia infection might be the etiology. A stool should also be obtained for ova and parasites, with special emphasis on the possibility of amebae or Giardia being present. In children, malabsorption is caused either by cystic fibrosis of the pancreas or celiac disease. In adults, the various forms of sprue and, more rarely, some of the secondary malabsorption causes might be considered. In children and young and middle-aged adults, ulcerative colitis is a possibility, especially if there is blood in the stools. This calls for a sigmoidoscopic or colonoscopic examination. In adults over age 40 years, carcinoma of the colon is the cause of diarrhea in a significant number of cases. A barium enema and colonoscopic examination are necessary. In the aged, in addition to carcinoma, fecal impaction is a frequent cause of diarrhea, and this usually can be determined easily by ordinary rectal examination.

One study reports that diarrhea is more frequent in patients with serum albumin levels less than 2.5 g/100 ml (25 g/L). Chronic diarrhea in diabetics occurs in 8%-22% of patients; in one study, about 50% had a known cause determined. It is more frequent in patients with poorly controlled diabetes treated with insulin who also have peripheral neuropathy and autonomic nervous system dysfunction. The diarrhea may be intermittent. Steatorrhea may or may not be associated. In many cases no organic etiology for persistent diarrhea can be found. This situation is often called “functional diarrhea” and is attributed to psychiatric causes. The organic diseases listed here must be ruled out before deciding that a patient has a psychosomatic disorder.

Differential Diagnosis of Diarrhea (More Frequent Etiologies)

Infection—bacterial
Salmonella, Shigella, Campylobacter, Yersinia enterocolitica, enteropathic Escherichia coli, Clostridium difficile enterocolitis.
Infection—virus
Rotovirus, fastidious enteric adenovirus, Norwalk virus
Infection—parasites
Giardia lamblia, Entamoeba histolytica
Ulcerative colitis—regional enteritis
Partial obstruction of colon
Colon carcinoma
Fecal impaction
Malabsorption—steatorrhea
Celiac disease: nontropical sprue, tropical sprue, disaccharide enzyme deficiency
Other
Diabetic neuropathy
Zollinger-Ellison syndrome
Hypoalbuminemia-associated

Persons infected by the human immunodeficiency virus 1 (HIV-1) often develop diarrhea, especially if they progress to the stages of disease known as acquired immunodeficiency syndrome (AIDS) or AIDS-related complex. Common infecting organisms in these patients are Mycobacterium avium, Mycobacterium intracellulare, Salmonella, Cryptosporidium, Microsporidium, cytomegalovirus, Giardia, Strongyloides stercoralis, and Isospora belli. However, numerous other organisms have been reported.