Porth's Essentials of Pathophysiology, 4e

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Disorders of Gastrointestinal Function

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6 weeks. 36 In most cases systemic manifestations are absent and the symptoms subside after the antibiotic has been discontinued. A more severe form of coli- tis, pseudomembranous colitis, is characterized by an adherent inflammatory membrane overlying the areas of mucosal injury. It is a life-threatening form of the disease. Persons with the disease are acutely ill, with lethargy, fever, tachycardia, abdominal pain and distention, and dehydration. The smooth muscle tone of the colon may be lost, resulting in toxic dilation of the colon. Prompt therapy is needed to prevent perforation of the bowel. The diagnosis of C. difficile colitis requires a care- ful history, with particular emphasis on antibiotic use. Diagnostic findings include a history of antibiotic use and laboratory tests that confirm the presence of C. difficile toxins in the stool. 33,34 Patients with C. diffi- cile infection should be put on contact precautions and placed in a single room with a bathroom or, if unavail- able, with other infected patients. 35 Treatment includes the immediate discontinuation of antibiotic therapy. Specific treatment aimed at eradi- cating C. difficile is used when symptoms are severe or persistent. Metronidazole is the drug of first choice, with vancomycin being reserved for persons who can- not tolerate metronidazole or do not respond to the drug. Both drugs are given orally. 33,34 Metronidazole is absorbed from the upper gastrointestinal tract and may cause side effects. Vancomycin is poorly absorbed, and its actions are limited to the gastrointestinal tract. Escherichia coli O157:H7 Infection. Enterohemor­ rhagic E. coli O157:H7 has become recognized as an important cause of epidemic and sporadic colitis. 6 E. coli O157:H7 is a strain of E. coli found in the feces and contaminated milk of healthy dairy and beef cattle, but it also has been found in contaminated pork, poultry, and lamb. Infection usually is by food-borne transmis- sion, often by ingesting undercooked ground beef. The organism also can be transferred to nonmeat products such as fruits and vegetables. Transmission has also been reported in persons swimming in a fecally con- taminated lake as well as among visitors to farms and petting zoos who are in direct contact with animals. Person-to-person transmission may occur, particularly in nursing homes, day care settings, and hospitals. The very young and the very old are particularly at risk for the infection and its complications. Although most strains of E. coli are harmless, E. coli 0157:H7 produce Shigella -like toxins that attach to and damage the mucosal lining of the intestine, caus- ing bloody diarrhea. 6,36,37 Subsequently, the Shigella -like toxins gain access to the circulatory system, where they damage the endothelium and initiate platelet activation. Two complications of the infection, hemolytic uremic syndrome and thrombotic thrombocytopenic purpura, reflect the effects of the Shigella -like toxins. The hemo- lytic uremic syndrome is characterized by hemolytic anemia, thrombocytopenia, and renal failure caused by platelet thrombi in the renal microvasculature. It occurs predominantly in infants and young children and is the most common cause of acute renal failure in children.

It has a mortality rate of 3% to 5%, and one third of the survivors are left with permanent disability. Thrombotic thrombocytopenic purpura is manifested by thrombocy- topenia, renal failure, fever, and neurologic manifesta- tions caused by microthrombi in the brain. No specific therapy is available for E. coli O157:H7 infection. Treatment is largely symptomatic and directed toward treating the effects of complications. The use of antibiotics or antidiarrheal agents in the early stages of diarrhea has been shown to increase the risk of hemo- lytic uremic syndrome because the gut is exposed to a greater amount of toxins for a longer time. Because of the seriousness of the infection and its complications, education of the public about techniques for decreas- ing primary transmission of the infection from animal sources is important. Undercooked meats and unpas- teurized milk are sources of transmission. Food handlers and consumers should be aware of the proper methods for handling uncooked meat to prevent cross-contam- ination of other foods. Particular attention should be paid to hygiene in day care centers and nursing homes, where the spread of infection to the very young and very old may result in severe complications. Diverticular Disease Diverticulosis is a disorder characterized by pseudodi- verticula of the colonic mucosa and submucosa. 6,7,38–40 Although the disorder is prevalent in the developed countries of the world, it is almost nonexistent in many African nations and underdeveloped countries. This suggests that factors such as lack of fiber in the diet, a decrease in physical activity, and poor bowel habits (e.g., neglecting the urge to defecate), along with the effects of aging, contribute to the development of the disease. True diverticula involve all layers of the intestinal wall. The abnormal structures in diverticulosis are instead pseudodiverticula, in which only the mucosa and submucosa are herniated through the muscle lay- ers. 6,7 The diverticula are often multiple, ranging from a solitary herniation to several hundred (Fig. 29-8). They are most often located in the sigmoid colon, but more extensive areas may be involved in severe cases. Microscopically, colonic diverticula are small, flasklike outpouchings, usually 0.5 to 1.0 cm in diameter, that occur in a regular distribution alongside the teniae coli (Fig. 29-9). Colonic diverticula result from the unique structure and elevated luminal pressures in the sigmoid colon. 6 In the colon, the longitudinal muscle does not form a continuous layer, as it does in the small bowel. Instead, there are three separate longitudinal bands of muscle called the teniae coli. In a manner similar to the small intestine, bands of circular muscle constrict the large intestine. As the circular muscle contracts at each of these points (approximately every 2.5 cm), the lumen of the bowel becomes constricted, so that it is almost occluded. The combined contraction of the circular muscle and the lack of a continuous longitudinal muscle