Paula O’Leary and Fergus Shanahan University College Cork, Cork, Ireland Immunodeficiency disorders are a heterogeneous group of conditions that may be classified broadly into primary and secondary syndromes. Selective immunoglobulin A (IgA) deficiency and common variable immunodeficiency (CVID) (Figures 68.1 and 68.2) are the most common primary immunodeficiency syndromes among adults. Secondary immunodeficiencies are much more common than primary disorders. Causes include malnutrition, infection (HIV), protein‐losing enteropathy such as intestinal lymphangiectasia (Figure 68.3), cancer, and iatrogenic immunosuppression. Figure 68.1 Small bowel biopsy specimen from a patient with hypogammaglobulinemia shows a paucity of plasma cells in the lamina propria. Among patients with selective immunoglobulin A (IgA) deficiency, the absence or paucity of IgA‐producing cells is compensated for by an increase in IgM‐producing cells. Source: Courtesy of Dr Klaus Lewin. The gastrointestinal tract is a primary target organ in both primary and secondary immunodeficiency disorders because of its large surface area and constant exposure to environmental pathogens. The gut mucosa is composed of the single largest collection of lymphoid tissue in the body, primed to respond effectively to microbial challenge while at the same time regulated closely to avoid inappropriate and potentially harmful immune responses to the extensive and varied exposures experienced at this host–environment interface. The principal gastrointestinal consequence of immunodeficiency is increased susceptibility to infection. This includes infection with unusual agents, atypical manifestations of infection with commonly encountered pathogens, and bacterial overgrowth with organisms normally present in the gastrointestinal tract. There is also an increased prevalence of autoimmune disorders or chronic inflammatory conditions such as atrophic gastritis, inflammatory bowel disease, and celiac disease. In some immunodeficiency states, there is an increased incidence of malignant tumors, particularly lymphoma. Benign diffuse nodular lymphoid hyperplasia may occur among some patients, whereas lymphoid atrophy may be a feature among others. Patients with severe immunodeficiency may have graft‐versus‐host disease caused by transplacentally acquired maternal lymphocytes or unintentional transfusion of nonirradiated blood products. However, patients with mild or selective forms of immunodeficiency, such as selective IgA deficiency, frequently are free of infections or other manifestations. Diffuse nodular lymphoid hyperplasia occurs among approximately 20% of patients with CVID. The lymphoid nodules are in the lamina propria and submucosa and produce a nodularity that is visible on radiographic studies and at endoscopy (Figure 68.4). They are most prevalent in the small bowel, in some cases extend into the colon, and rarely extend into the stomach. At microscopic examination, the nodules consist of large lymphoid follicles with germinal centers (Figure 68.5). Plasma cells are usually absent. Lymphoid hyperplasia is believed to be caused by proliferation of B cells that are unable to undergo full differentiation to immunoglobulin secretion and therefore are unresponsive to feedback regulation of proliferation. Figure 68.2 (a,b) Giardiasis (Giardia lamblia) is the most common gastrointestinal parasitic infection in primary immunodeficiency syndromes. It occurs most frequently among patients with common variable hypogammaglobulinemia. Giardiasis usually does not distort the villous structure but may do so among patients with immunodeficiencies. Although the diagnosis of giardiasis can be made from inspection of histological sections of small bowel, finding the organism by means of this method is difficult and tedious when the infection burden is low. The diagnosis is made more conveniently by examination of stool for cysts or identification of the trophozoite form in intestinal fluid or smears of mucus adherent to the biopsy specimen. Figure 68.3 Secondary immunodeficiency – intestinal lymphangiectasia. Immunodeficiency caused by enteric protein loss may be a component of any severe inflammatory disorder of the gastrointestinal tract. The most severe cases of gastrointestinal protein loss occur with lymphangiectasia, which may be primary or secondary to lymphatic obstruction. Protein loss from the gastrointestinal tract is nonselective, and hypogammaglobulinemia is always accompanied by hypoalbuminemia. Among patients with lymphangiectasia, there is also loss of lymphocytes, particularly T cells, and immunoglobulins. Source: Mitros FA. Atlas of Gastrointestinal Pathology. London: Gower, 1988. Reproduced with permission of Elsevier.
CHAPTER 68
Gastrointestinal manifestations of immunological disorders
Immunodeficiency
Nodular lymphoid hyperplasia
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