Diarrhea

Abnormal looseness (liquidity) of the stool, which may be accompanied by a change in stool frequency or volume.

Diarrhea is a subjective symptom; some patients experiencing a primary difficulty with fecal continence may describe their condition as "diarrhea." Associated symptoms include urgency, cramping, bloating, and incontinence. Dysentery refers to painful, bloody, low-volume diarrhea. Antibiotic-associated diarrhea is discussed in Ch. 107.

The incidence of diarrhea in the elderly is unknown. The elderly may be more susceptible to infectious diarrhea, because they more often have hypochlorhydria and achlorhydria (eg, from pernicious anemia or gastric acid-suppressing drugs), luminal stasis (eg, from motility disorders or previous surgeries), or decreased mucosal immune function. Diarrhea is a major cause of morbidity and mortality in the elderly. Nursing home outbreaks of Escherichia coli O157:H7 infection have been documented with three times the morbidity and mortality than in younger persons. The higher mortality rate (16 to 35%) occurs largely because the elderly are less capable of replenishing their fluid losses and tolerating the intravascular hypovolemia associated with dehydration.

Classification and Etiology

Diarrhea is classified on the basis of duration as acute (< 2 weeks) or chronic (> 4 weeks). There are many causes of diarrhea in the elderly (see Table 110-4); however, even in severe cases, a cause cannot be identified in about 25% of patients.

Acute diarrhea: Most diarrhea in the elderly is acute and self-limited. It is usually due to infection (viral, bacterial, or parasitic), a recent drug change, or a food intolerance. Food intolerance may occur when elderly persons eat large amounts of fruits or beans. Acute bloody diarrhea may be caused by ischemia (eg, mesenteric thrombosis or ischemic colitis), diverticulitis, or inflammatory bowel disease.

Viruses responsible for infectious diarrhea include the Norwalk virus-like agents and, less commonly, rotavirus. The exact pathogenetic mechanism is unclear. Diarrhea is caused by Norwalk virus throughout the year; diarrhea due to rotavirus is more common in cooler months. Both viruses are spread easily by the fecal-oral route and have caused epidemic diarrhea in nursing homes.

Toxigenic diarrhea has two forms: food poisoning due to ingestion of food contaminated with preformed bacterial enterotoxin (due to Staphylococcus aureus, Bacillus cereus, or Clostridium perfringens) and infectious gastroenteritis caused by enterotoxin-producing bacteria (E. coli, Clostridium difficile, Vibrio cholerae, Clostridium botulinum, or Vibrio parahaemolyticus). Invasive diarrhea may be caused by Shigella, Salmonella, Campylobacter, or Yersinia.

Chronic diarrhea: Diarrhea is classified as secretory (isosmolar to plasma) or osmotic (hyperosmolar to plasma). Chronic diarrhea is categorized as watery, bloody, or fatty.

Secretory diarrhea is caused by agents that trigger intestinal epithelial cells to secrete water and electrolytes into the intestinal lumen. Examples in the elderly are diarrhea secondary to increased secretion of hormones, peptides, or biogenic amines from tumors, including carcinoid tumors, medullary carcinoma of the thyroid, islet cell tumors of the pancreas (eg, vipoma (see Table 113-1)) and gastrinoma [Zollinger-Ellison syndrome]), (see Table 113-1) parathyroid adenoma, and small cell carcinoma of the lung; bile acid-induced diarrhea, idiopathic, or after resection of > 100 cm of the distal ileum; postobstructive diarrhea; or diarrhea due to villous adenoma of the distal colon.

Medications are a common cause. Although almost any drug can cause diarrhea, more common offenders include nonsteroidal anti-inflammatory drugs (NSAIDs), magnesium-containing antacids, antiarrhythmics, -blockers, quinidine, and digoxin.

Microscopic colitis is a cause of chronic persistent watery diarrhea. The etiology is unknown, but the condition is sometimes induced by drugs and may be associated with NSAIDs. Collagenous colitis and lymphocytic colitis may represent different stages of microscopic colitis and can be differentiated based on the histologic appearance. Characteristic changes in both disorders include increased plasma cells and intraepithelial lymphocytes. In collagenous colitis, a distinct subepithelial collagen band is also present. Collagenous colitis has a male:female incidence ratio of about 1:10, whereas lymphocytic colitis has a ratio of about 1:1. Symptoms are crampy abdominal pain and, often, a prolonged chronic watery diarrhea. The colonic mucosa appears grossly normal on colonoscopy.

Small-bowel bacterial overgrowth (see Table 111-1) causes chronic secretory or fatty diarrhea. The diarrhea is often described as fatty because of the deconjugation of bile salts by the bacteria. Predisposing conditions include gastric achlorhydria, prior gastric surgery, and small-bowel diverticulosis.

Patients with long-standing diabetes mellitus can develop diarrhea due to intestinal neuropathy, although constipation is much more common among these patients. Other causes of pseudo-obstruction in which diarrhea may be a presenting symptom include collagen vascular disease (eg, scleroderma), neurologic disorders, primary muscle diseases (eg, muscular dystrophy), and pseudo-obstruction of the small bowel.

Less commonly reported causes in the elderly are irritable bowel syndrome and certain infections (eg, giardiasis and, in immunosuppressed patients, microsporidiosis, cryptosporidiosis, and Mycobacterium avium-intracellulare); 10% of AIDS patients are elderly, and these infections occur often in AIDS patients.

Osmotic diarrhea results from the ingestion of osmotically active ingredients in certain foods and drugs. In the elderly, osmotic diarrhea is typically caused by the ingestion of poorly absorbable solutes (eg, magnesium sulfate, sodium sulfate), laxatives containing citrate, antacids containing magnesium hydroxide, and some sugars (eg, mannitol, sorbitol, and fructose, which may be found in antacids, chewing gum, diet candy, and fruits).

Disaccharidase deficiencies, especially lactase deficiency, can also cause osmotic diarrhea. About 80% of the world population has primary lactase deficiency. Black Americans and Jews have the highest incidence. The condition begins in childhood and cannot be outgrown.

Osmotic diarrhea also occurs after a gastrectomy or vagotomy, in dumping syndrome, in short-bowel syndrome, and with chronic small-bowel ischemia or small-bowel resection.

Bloody (exudative, inflammatory) diarrhea contains blood and leukocytes; it results from injury and inflammation of the mucosal tissues of the distal ileum and colon. Causes in the elderly include inflammatory bowel disease (ulcerative colitis and Crohn's disease), ischemic colitis, carcinoma of the colon, and radiation colitis.

Several infections may progress to chronic bloody diarrhea (eg, Campylobacter jejuni, C. difficile, Yersinia enterocolitica, cytomegalovirus, and Entamoeba histolytica).

Fatty diarrhea is due to the maldigestion or malabsorption of dietary fat. Stools are of large volume and malodorous, with floating fat droplets. Pancreatic exocrine insufficiency (especially lipase deficiency) is the prototypic disease causing fat maldigestion. Fat is malabsorbed in the setting of deficient bile salts (biliary tract obstruction, cholestatic liver disease, ileal disease) and small-bowel mucosal disease (eg, gluten-sensitive enteropathy, celiac disease, tropical sprue, giardiasis, Crohn's disease, Whipple's disease). Patients with maldigestion or malabsorption often report weight loss despite normal or enhanced food intake.

Diagnosis

Evaluation is indicated for patients with moderate or severe illness when clinical symptoms suggest bacterial infection, for larger volume (>= 6 stools/24 hours) or bloody diarrhea, and for acute diarrhea lasting > 8 hours.

Diagnosing the cause of diarrhea is challenging. The initial evaluation should first determine whether the patient's problem is diarrhea, fecal incontinence, or fecal impaction with overflow incontinence. Next, to help categorize the diarrhea and narrow the differential diagnosis, the characteristics of the diarrhea are determined. In the elderly, serious diarrhea that leads to dehydration may require hospitalization for further evaluation and treatment.

The history and physical examination provide clues to the etiology and determine the severity of the diarrhea. A temporal relationship should be sought between the onset of diarrhea and the introduction of new drugs. Symptoms from food poisoning usually develop within 6 to 12 hours of ingestion, while symptoms from Salmonella, Y. enterocolitica, or Campylobacter usually develop 12 to 48 hours after ingestion. Bloody stools suggest significant inflammation or ulceration, as can occur with ischemic colitis or infection with Shigella, E. histolytica, or enteroinvasive E. coli; patients with a recent history of antibiotic use are at risk for C. difficile diarrhea. The presence of atherosclerotic vascular disease, abdominal bruits, and initial painless bleeding suggests colonic ischemia. Significant abdominal tenderness requires prompt evaluation for the underlying etiology.

Initial laboratory tests may include a CBC, biochemical test of electrolytes, renal function, and nutritional parameters (ie, albumin, calcium, phosphorus, total protein). Stool samples are tested for occult blood; white blood cells; qualitative fat (Sudan stain); and, in patients with a recent history of antibiotic use, hospitalization, or institutionalization, C. difficile toxin. Stool electrolytes (sodium and potassium) obtained on spot samples of stool are used to calculate an osmotic gap with the following formula: 290 - 2 (Na + K).

Stool cultures are indicated in patients with severe diarrhea and fever, bloody stools, fecal leukocytes, or prolonged illness (> 14 days). Stool samples should be obtained for testing of ova and parasites in patients who travel extensively or live in an endemic area (three fresh samples are required for a 90% sensitivity). When giardiasis is suspected, an enzyme-linked immunosorbent assay for Giardia antigen is more sensitive than routine ova and parasitic testing.

When the diagnosis of diarrhea remains obscure, the single most useful test is the quantitative stool collection, typically the 72-hour fecal fat collection. Information can be obtained about total stool weight and the efficiency of fat absorption. Fecal fat concentrations of > 9.5 g/100 g of stool suggest pancreatic insufficiency or biliary steatorrhea.

Flexible sigmoidoscopy may be helpful in some acute cases to evaluate for evidence of pseudomembranes or ischemia.

Secretory diarrhea typically has an osmotic gap of < 50. When the clinical picture suggests a hormone-secreting tumor, serum tests for gastrin, calcitonin, and vasoactive intestinal polypeptide and urine collection for 5-hydroxyindoleacetic acid, metanephrine, or histamine may be helpful.

Osmotic diarrhea has an osmotic gap of > 125. Stool pH of < 5.3 (normal is > 6) supports the diagnosis of carbohydrate malabsorption. In lactase deficiency, the stool pH is usually 4 to 6 with an associated increase in short-chain fatty acids. A lactose-hydrogen breath test reveals breath hydrogen > 20 ppm within 3 hours after lactose ingestion. Measuring magnesium, sulfate, and phosphate in stool water may be necessary in cases of surreptitious laxative abuse, a problem more common in elderly women.

Bloody (exudative) diarrhea (fecal blood and leukocytes) and fatty diarrhea (Sudan stain) require further evaluation. A plain abdominal x-ray may show pancreatic calcification indicating chronic pancreatitis (due to alcohol or familial pancreatitis). A small-bowel follow-through examination may show ileal disease (Crohn's disease) or mucosal thickening (eg, small-bowel lymphoma). Colonoscopy enables direct visualization and biopsy of the colonic mucosa and is the procedure of choice for diagnosing radiation proctopathy, inflammatory bowel disease, and colorectal tumors. Biopsy samples obtained from normal-appearing colonic mucosa can be examined for changes of microscopic colitis.

Upper gastrointestinal endoscopy is helpful in obtaining small-bowel biopsies for suspected mucosal disease (eg, celiac sprue, Whipple's disease (see Table 111-1)). Small bowel aspirates can be obtained at the same time to evaluate for small bowel bacterial overgrowth and parasites.

Serum tests of antigliadin immunoglobulin (IgA and IgG) antibodies and antiendomysial IgA antibodies are helpful in the diagnosis and treatment of patients with celiac sprue.

In patients with chronic fatty diarrhea, pancreatic exocrine insufficiency can be determined by administrating secretin or cholecystokinin IV and aspirating duodenal contents for bicarbonate and pancreatic enzyme concentration. This test is cumbersome but remains the standard for assessing pancreatic exocrine function. Although not sensitive in mild and moderate disease, measurement of chymotrypsin or elastase activity in stool samples can also assess pancreatic function.

Treatment

The first management priority for patients with diarrhea is fluid and electrolyte replacement. Patients who can take drugs orally should be given oral rehydration solutions. Elderly patients with symptomatic fluid losses require close monitoring and usually hospitalization. Food poisoning is self-limited, usually of brief symptomatic duration, and is treated using fluid support.

Antibiotic treatment for infectious diarrhea is listed in Table 110-5. Empiric antibiotic treatment is indicated for patients with fever, evidence of systemic toxicity, bloody stool, or traveler's diarrhea; the usual drug of choice is a fluoroquinolone for 3 to 5 days. Although treatment can begin immediately, it is helpful to obtain a stool sample for bacterial culture first.

If toxin-producing or invasive bacteria are not suspected, antidiarrheal drugs can be given safely (see Table 110-5). Empiric treatment can minimize diarrheal symptoms when the diagnostic evaluation is in progress, when a diagnosis has been made but specific treatment is unavailable, or when testing fails to reveal a diagnosis. Various prescription drugs and over-the-counter products are available. Soluble fiber (eg, psyllium) adds form to the stool. Synthetic opioids loperamide and diphenoxylate are excellent first-line drugs. Loperamide is generally preferred, because the usual formulation of diphenoxylate incorporates atropine, which can cause significant adverse effects in elderly persons. When the diarrhea cannot be controlled with these drugs, stronger opioids (eg, codeine, tincture of opium) are recommended. Because of its need for injection and increased adverse effects, somatostatin analog is a second-line drug for the treatment of chronic idiopathic diarrhea. When bile acid diarrhea is suspected, cholestyramine may be tried.

Treatment of microscopic colitis consists of removing the offending agent when it is identified and use of antidiarrheal drugs. Clinical improvement is reported with 5-aminosalicylate drugs. Corticosteroids are generally avoided.