Tuberculosis

Intestinal tuberculosis (TB) is most common in patients with active pulmonary disease and is caused by swallowed organisms that cross the mucosa of the bowel segments rich in lymphoid tissue, that is the ileum and cecum.

Tuberculosis within the gastrointestinal (GI) tract can be divided into four main types: tubercular lymphadenopathy, peritoneal tuberculosis, visceral tuberculosis, and gastrointestinal tuberculosis. Ileocecal TB is the most common location for GI TB, occurring in 64% of GI TB, followed by the jejunum and colon. The tissue response can be hypertrophic, ulcerative, or a combination of both. When tuberculosis becomes disseminated (miliary tuberculosis), tubercles are found on the serosal surface of the bowel. (Figures 26.1 and 26.2).

Whipple disease

Whipple disease is a rare chronic multisystem disease caused by infection with Tropheryma whipplei. The most important step in the evaluation of Whipple disease is to have a high degree of suspicion in the appropriate clinical setting. Given the wide spectrum of clinical presentations of this disease, the challenge is to establish the correct diagnosis. A variety of nonspecific laboratory findings are to be expected.

In classic Whipple’s disease, small bowel mucosal biopsy usually establishes the diagnosis. The disease is usually diffuse but can be patchy; therefore, multiple (4–6) biopsy specimens should be obtained. The characteristic duodenal mucosal folds are pale yellow, brown or shaggy with a granular appearance with intermittent superficial erythematous patches. (Figure 26.3). Chromoendoscopy using narrow‐band imaging can reveal the presence of flattened, engorged villi displaying characteristic concentric rings in villus structure (Figure 26.4). Pseudopolyploid surface features, erosions, and loss of villi have been described. The appearances can be patchy and discontinuous along the length of the small bowel.

The appearance with periodic acid–Schiff (PAS) staining often is sufficient to establish the diagnosis of Whipple disease for most patients (Figures 26.5 and 26.6); however, it can be confirmed with electron microscopic demonstration of the bacilli (Figure 26.7). Heavy infiltration of the small bowel lamina propria with macrophages containing PAS‐positive inclusions is typical. However, the appearances can be variable and multiple biopsies should be examined. Occasional macrophages are found in the normal intestinal lamina propria; these usually stain faintly PAS positive but the inclusions are not sickle shaped as in Whipple disease.

There are three differential diagnoses in which numerous PAS‐positive macrophages in the intestinal laminia propia may be deceptive. Mycobacterium avium complex (MAC) infections are seen in immunodeficiency syndromes, especially HIV infection, systemic histoplamosis and macroglobulinemia. In MAC infection, the lamina propria is packed with macrophages containing MAC, which when stained with hematoxylin and eosin and PAS stain clearly resemble those seen in Whipple disease. However, MAC organisms are morphologically different from T. whipplei on electron microscopy and these organisms are acid fast and can be cultured. (Figure 26.8). T. whipplei infection has not been reported among persons with HIV infection.

Macroglobulinemia can be differentiated from Whipple disease because of the faintly staining, homogeneously PAS‐positive macrophages, and histoplasmosis can be differentiated by the large, PAS‐positive, rounded, encapsulated Histoplasma organisms.

PAS‐positive macrophages are frequently present in the normal gastric and rectal mucosa, and in many diseases of the stomach and rectum, so caution is advised in interpreting these findings. The stomach often contains faintly PAS‐positive, lipid‐containing macrophages (lipophages), whereas the rectal mucosa usually contains strongly PAS‐positive muciphages and pigment‐containing macrophages (Figure 26.9). Electron microscopic demonstration of Whipple bacilli in these tissues usually is necessary to establish the diagnosis (see Figure 26.7).

Barium studies of the small intestine usually are abnormal in Whipple disease and may reveal a characteristic but nonspecific finding of marked thickening of the mucosal folds (Figure 26.10). These findings usually are more prominent in the duodenum and proximal jejunum and less prominent in the distal jejunum; the ileum is spared.

Histoplasmosis

Histoplasmosis is primarily a pulmonary opportunistic infection that can become disseminated in immunocompromised patients. The small intestine is reportedly involved in 20% of cases of disseminated histoplasmosis, but just 3–12% of affected patients have intestinal symptoms. The symptoms most commonly described in small intestinal histoplasmosis include weight loss, diarrhea, fever, abdominal pain, nausea, vomiting, and malaise. Protein‐losing enteropathy, malabsorption, and steatorrhea have also been documented. The stools are typically unformed or semiformed, while hematochezia suggests colonic involvement.

Gastrointestinal tract involvement should be considered in patients with positive blood cultures for H. capsulatum, confirmed H. capsulatum antigenemia, antigenuria or H. capsulatum

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