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.