Porth's Essentials of Pathophysiology, 4e

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Gastrointestinal and Hepatobiliary Function

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CT scans may be used to detect an inflammatory mass, fistula, or abscess. Radiographic contrast studies may be used to augment endoscopy or CT scans. Treatment methods focus on terminating the inflam- matory response and promoting healing, maintaining adequate nutrition, and preventing and treating compli- cations. Nutritional deficiencies are common in Crohn disease because of diarrhea, steatorrhea, and other mal- absorption problems. A nutritious diet that is high in calories, vitamins, and proteins is recommended. Because fats often aggravate the diarrhea, it is recommended that they be avoided. Elemental diets, which are nutritionally balanced but residue free and bulk free, may be given dur- ing the acute phase of the illness. 8 These diets are largely absorbed in the jejunum and allow the inflamed bowel to rest. Total parenteral nutrition (i.e., parenteral hyperali- mentation), which is administered intravenously, may be needed when food cannot be absorbed from the intestine. 8 Several medications have been successful in sup- pressing the inflammatory reaction in Crohn disease, including 5-aminosalicylic acid (5-ASA) agents, cor- ticosteroids, antibiotics, immunosuppressant drugs (azathioprine, 6-mercaptopurine, methotrexate), and anti–tumor necrosis factor (TNF) therapies (infliximab and adalimumab). 8,28 The 5-ASA agents act locally to affect multiple sites in the arachidonic acid pathway crit- ical to the pathogenesis of inflammation. Much of the unformulated 5-ASA is absorbed from the small intes- tine and does not reach the distal small bowel or colon in appreciable amounts. To overcome the rapid absorp- tion of 5-ASA, a number of formulations (e.g., sulfasala- zine, mesalamine) have been designed to deliver the drug to the distal small bowel and colon. Corticosteroids are used to suppress the acute clinical symptoms in persons with small and large bowel disease. Metronidazole is an antibiotic used to treat bacterial overgrowth in the small intestine. Azathioprine, 6-mercaptopurine, methotrex- ate, and cyclosporine are immunomodulating drugs that are used in persons who do not respond to other forms of therapy. 8 The anti-TNF agents are monoclonal anti- bodies that target the destruction of TNF- α , a mediator of the inflammatory response that is known to be impor- tant in granulomatous inflammatory processes such as Crohn disease. 8 These agents are used to treat severe disease. Surgical resection of damaged bowel, drainage of abscesses, or repair of fistula tracts may be necessary. Ulcerative Colitis Ulcerative colitis is a nonspecific inflammatory condition of the colon. The disease is more common in the United States and Western countries. The disease may arise at any age, with a peak incidence in the third decade. 7 Unlike Crohn disease, which can affect various sites in the gastrointestinal tract, ulcerative colitis is confined to the rectum and colon. 6,7 The disease usually begins in the rectum and spreads proximally, affecting primarily the mucosal layer, although it can extend into the submuco- sal layer. The length of proximal extension varies. It may involve the rectum alone (ulcerative proctitis), the rec- tum and sigmoid colon (proctosigmoiditis), or the entire

been likened to a lead pipe or rubber hose. The adja- cent mesentery may become inflamed, and the regional lymph nodes and channels may become enlarged. The clinical course of Crohn disease is variable; often, there are periods of exacerbations and remis- sions, with symptoms being related to the location of the lesions. 6-8,28 The principal symptoms include inter- mittent diarrhea, colicky pain (usually in the lower right quadrant), weight loss, fluid and electrolyte disorders, malaise, and low-grade fever. 32 Because Crohn disease affects the submucosal layer to a greater extent than the mucosal layer, there is less bloody diarrhea than with ulcerative colitis. Ulceration of the perianal skin is com- mon, largely because of the severity of the diarrhea. The absorptive surface of the intestine may be disrupted; nutritional deficiencies may occur, related to the specific segment of the intestine involved. When Crohn disease occurs in childhood, one of its major manifestations may be retardation of growth and physical development. Complications. Complications of Crohn disease include fistula formation, abdominal abscess formation, and intestinal obstruction. Fistulas are tubelike passages that form connections between different sites in the gas- trointestinal tract. They also may develop between other sites, including the bladder, vagina, urethra, and skin. Perineal fistulas that originate in the ileum are relatively common. Fistulas between segments of the gastrointesti- nal tract may lead to malabsorption, syndromes of bac- terial overgrowth, and diarrhea. They also can become infected and cause abscess formation. Diagnosis andTreatment. The diagnosis of Crohn dis- ease requires a thorough history and physical examina- tion. Endoscopy is used for direct visualization of the affected areas, to determine extent of disease involvement, and to obtain biopsies. Measures are taken to exclude infectious agents as the cause of the disorder. This usually is accomplished by the use of stool cultures and exami- nation of fresh stool specimens for ova and parasites. FIGURE 29-6. Crohn disease. A longitudinal ulcer of terminal ileum.The larger rounded areas of edematous damaged mucosa give a “cobblestone” appearance in the involved mucosa. A portion of the mucosa in the lower right is uninvolved. (From Rubin R.The gastrointestinal tract. In: Rubin R, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of Medicine. 6th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &Wilkins; 2012:654).