Figure 3.153 Eosinophils in the lamina propria. Eosinophils are bi-lobed leukocytes with abundant brightly eosinophilic granules that make them easily identifiable at low magnification. They are a normal inhabitant of the small bowel lamina propria, but areas of intense clustering, intraepithelial eosinophils, or eosinophilic abscesses may indicate an underlying disease state.
CHECKLIST: Etiologic Considerations for the Eosinophilia Pattern
Idiopathic Eosinophilic Enteritis
Medications
Allergy
Parasitic Infection
Inflammatory Bowel Disease
Connective Tissue Disorders and Vasculitis
The eosinophilia pattern is broadly defined as excessive numbers of eosinophils in a normal location (i.e., lamina propria) or any eosinophils in an abnormal location (i.e., epithelium or muscularis mucosae) (Fig. 3.153). Eosinophil numbers show an upward gradient from the esophagus to the small bowel.78 Currently, there are no vigorous standards for the threshold of increased eosinophils in the small bowel, although some studies employ >20 eosinophils in one high powered field.79 Low-level eosinophilia is relatively common in routine biopsies and studies have shown an association with allergy and hypersensitivity in patients.78–84 Nonetheless, compared to other gastrointestinal sites, there is a relative paucity of information regarding eosinophilia in the small bowel, and diagnoses are frequently descriptive and operator-dependent (Figs. 3.154–3.157). Until further study clarifies the significance of small bowel eosinophilia, the differential diagnosis broadly overlaps with that of gastric eosinophilia. For this reason, readers are referred to the Eosinophilia Pattern, Stomach Chapter.
Figure 3.154 Mucosal eosinophilia, medication-related (arrowhead). Review of a patient’s medication list may provide etiologic clues for mucosal eosinophilia. In this example, the patient was taking the immunosuppressant mycophenolate mofetil, which has a known association with mucosal eosinophilia.
Figure 3.155 Mucosal eosinophilia, medication-related (arrowheads). Mucosal eosinophilia is nonspecific without clinical context. This example is from a patient on a chemotherapeutic regimen for chronic lymphocytic leukemia who presented with a skin rash and gastrointestinal symptoms. The findings likely represent medication-related mucosal eosinophilia.
Figure 3.156 Duodenal eosinophilia in a patient with eosinophilic esophagitis. This duodenal biopsy shows mild villous blunting and marked expansion of the lamina propria by an inflammatory infiltrate.
Figure 3.157 Duodenal eosinophilia in a patient with eosinophilic esophagitis (EoE). Higher magnification of the previous figure shows abundant mucosal eosinophils in the lamina propria (arrows). The patient has an established diagnosis of EoE, and the duodenal findings raise the possibility of a more generalized idiopathic eosinophilic enteritis.
SAMPLE NOTE: DUODENAL EOSINOPHILIA PATTERN OF INJURY, MILD, NOS
Duodenum, Biopsy:
• Duodenal mucosa with increased eosinophils.
Note: The presence of eosinophils in the gastrointestinal tract is a nonspecific finding and has been associated with food allergy, medication reaction, parasitic infection, Crohn disease, hematologic or lymphoid disorders, and connective tissue disorders. Some cases remain idiopathic, and exclusion of involvement of other sites in the gastrointestinal tract (i.e., stomach and colon) may be of interest. Correlation with clinical and serologic information is recommended.