History and Physical Examination



The patient’s description (or better yet, the phy­sician’s observation) of the diarrheal stool is often informative. Large, voluminous stools suggest a small bowel or proximal colon source, whereas small stools associated with frequent urges to de­fecate suggest disease in the left colon or rectum. Blood suggests mucosal inflammation, whereas frothy stools and flatus suggest carbohydrate mal­absorption. Greasy, foulsmelling stools with vis­ible oil or fat indicate severe steatorrhea. A thor­ough drug history is also important as antibiotics, antacids, antihypertensive agents, thyroxine, dig­italis, propranolol, quinidine, colchicine, lactu­lose, ethanol, and laxatives may be associated with diarrhea. Other pertinent information in­cludes the time course of the present illness (acute or chronic), previous surgery, systemic com­plaints, recent travel, family history, and sexual orientation (male homosexuals have a high inci­dence of intestinal infections; see below). For ex­ample, acute diarrhea is usually due to infectious agents or toxins (food poisoning) whereas chronic diarrhea is not.

The physical examination may provide clues to the diagnosis of diarrhea, many of which are given in.
Although the cause of diarrhea may be apparent from information obtained through the history and physical examination, selected laboratory tests are often needed to establish or confirm a diagnosis. Table 36-11 lists a number of tests that may be useful in evaluating diarrhea, although for most patients only a few of these will be neces­sary. In selecting appropriate tests, it is useful to categorize patients into two categories: (1) Those with acute diarrhea, generally due to infection, drugs, food poisoning, and fecal impaction. Trav­eler’s diarrhea is a specific subset of this group which occurs within {wo weeks of travel to a trop­ical or developing area and runs a self-limited course of one to ten days. (2) Those with chronic diarrhea, which in turn may be divided into (a) secretory diarrhea, generally due to drugs, hor­mones, bile acids, or fatty acids; (b) osmotic diar­rhea, generally due to drugs, laxatives, or mal­absorption; (c) inflammatory diarrhea due to inflammatory bowel disease (ulcerative colitis, Crohn’s disease), ischemic colitis, or parasitic in­fection; (d) motility disorders such as irritable bowel syndrome, scleroderma, and diabetic au­tonomic neuropathy.

Tests that should be performed on all patients include examination of the stool for consistency, fecal leukocytes (Wright’s stain), and blood. In pa­tients with acute diarrhea, fecal leukocytes sug­gest either infection with invasive organisms such as Shigella, Escherichia coli, Entamoeba histo­lytica, gonococci, or Campylobacter, or anti­biotic-associated colitis. In patients with chronic diarrhea, pus suggests colitis such as ulcerative colitis, Crohn’s disease, or ischemic colitis. Pus is not seen in toxin-induced secretory diarrhea, mal­absorption, laxative abuse, or giardiasis. Fecal blood generally indicates inflammation and has the same significance as pus.

The physician selects further tests depending upon the clinical picture. Patients with acute diar­rhea, in whom an infectious cause is likely, should have stools examined for ova and parasites and appropriately cultured for bacterial patho­gens. Proctosigmoidoscopy is generally of little help in acute diarrhea except to visualize pseu-domembranes in antibioticassociated diarrhea.

Blood cultures and a white blood cell and differ­ential count may be useful in individuals with signs of systemic infection, while serological tests for amebiasis are helpful as they are usually pos­itive in the presence of tissue invasion.

In evaluating chronic diarrhea, the initial se­lection of tests is designed to answer the following questions: (1) Is diarrhea secretory or osmotic? Evaluate the effect of fasting and measure the fecal osmotic gap. (2) Is malabsorption present? Eval­uate stool fat and D-xylose absorption. (3) Are structural, mucosal, or motility abnormalities present? Evaluate appearance with radiographic or endoscopic procedures and biopsies if appro­priate. The answers to these questions will deter­mine selection of the more specific and special­ized tests listed in Table 36-11. Certain of these tests deserve brief discussion.

Stool examination and culture should always precede enemas or radiographic studies, as fluid or barium may interfere with demonstration of pathogens. Similarly, proctosigmoidoscopy, which rapidly allows examination and biopsy of the distal colon, should be performed without enemas or other preparation, as these may distort or obscure evidence of disease. Mucosal smears may be obtained at sigmoidoscopy for culture and examined for pus. Rectal biospies may be per­formed to detect amyloidosis, Whipple’s disease, inflammation, or schistosomiasis.

Quantitative fecal fat determination (see Sec­tion C of this chapter) is one of the most sensitive tests for steatorrhea and, if elevated, the differ­ential diagnosis of malabsorption should be pur­sued. Test results must be interpreted in light of dietary fat intake, which is usually standardized at 100 grams per day for the entire three days of the collection. Other tests for malabsorption are discussed in Section C of this chapter.

Hormone assays (vasoactive intestinal polypep­tide, prostaglandins, calcitonin, gastrin, and oth­ers) are likely to be helpful only in the rare subgroup of patients with chronic, severe (>1 liter per day) secretory diarrhea in whom laxative abuse and intrinsic gastrointestinal tract disease have been ruled out.

Therapeutic trials may also be indicated in cer­tain cases as diagnostic tests, including pancreatic enzymes (for pancreatic exocrine insufficiency), antibiotics (for bacterial overgrowth), metronida­zole (for giardiasis), cholestyramine (for bile acid malabsorption), and various diets (lactose-free).