Discussion
Eosinophilic enteritis is an uncommon disease in horses. The number of case reports described in the literature is scant. The disease is characterized by the infiltration of eosinophils into the equine intestinal tract, producing one or several circumferential mural bands in the small intestine that cause obstruction .
In this case report, ultrasonography showed distended loops of small intestine and an unknown structure associated with a small intestine lumen with a mixed echogenicity material. The surgical findings indicated the mixed echogenicity was a mural hematoma, focally present, and collapsing the lumen of the involved jejunum. The few case reports in the literature showed surgical findings of striking hyperemic, circumferential bands with histological evidence of submucosal edema, mucosa swelling, and hemorrhage (Bont et al., 2016).
The intramural hemorrhage found in this case had caused an obstruction and necrosis in the affected segment. The cause of the hemorrhage is unknown, and it is believed that it is secondary to eosinophilic enteritis. The necrosis of the affected segment has not been described in literature as a characteristic of focal eosinophilic enteritis . However, the intramural hemorrhage and the consequent obstruction caused necrosis in this case due to the decreased blood flow into the affected segment. Intramural hematomas in humans are not frequent, but the few cases described are often attributable to a complication of anticoagulant therapy and less common bleeding diatheses, abdominal trauma, infarction, and vasculitis (Yoldas et al., 2013).
Eosinophilia in horses has been attributed to internal parasitism, cutaneous habronemiasis, systemic hypersensitivity reaction, lymphosarcoma, and eosinophilic leukemia (Sharkey and Overmann, 2015). Internal parasitism is the leading cause of eosinophilia in horses ; but in this case, no specimen was detected. Eosinophilic enteritis has been associated with geographical regions and seasons, most commonly between late spring and early fall. In the United States, the seasonal distribution of cases corresponds to the grazing period, suggesting a dietary association .
Eosinophilic enteritis has been attributed to food allergies in humans. Patients report intense pain in the abdomen that did not respond to treatment. Biopsies of these patients were sent to histopathology, confirming eosinophilia in the ileum and unspecific colitis. After the results, the patients were treated with corticosteroids and mesalamine (5-aminosalicylic acid (5-ASA), medication used to treat ulcerative colitis and showed significant improvement (Laud et al., 2020).
Food allergies in horses can produce immunologic reactions. The allergen must breach the intestinal mucosal barrier to expose it to the immune system. An abnormal immune response can lead to hypersensitivity. Typically, the gastrointestinal system has different mechanisms to avoid this breach. However, in some cases, such as in older horses where the mucosal barrier has begun to degenerate, or in animals with gastrointestinal diseases that have damaged the intestinal barrier, macromolecules can pass through and reach the immune system .
Finally, while the underlying cause of the enteritis and subsequent hematoma is unknown in this case, we hypothesize that due to the age of the mare and the season in which the disease developed, an underlying hypersensitivity such as food allergy may have played a role based on literature and histopathological examination. Damage to the mucosal barrier of the intestine may have led to an immunologic reaction and subsequent eosinophilic enteritis. Enteritis led to a loss of integrity of the associated vasculature as indicated by the myxomatous change seen on histopathology. Ultimately these vessels began leaking into the wall of the jejunum, subsequently causing mural hematoma and obstruction resulting in necrosis of the segment. Furthermore, the last histopathology report showed that the mare continued to produce eosinophilic infiltration in the submucosa and granulomas that contained hemosiderin-laden macrophages in the serosa. In conclusion, as hypothesized previously, due to a possible hypersensitivity, it is suspected that the mare would have developed eosinophilic enteritis and secondary intramural hematoma again.