Background: Histiocytic ulcerative colitis (HUC), also known as granulomatous Boxer’s colitis or colitis similar to Whipple’s
disease is a condition affecting especially Boxer dogs. The disease is characterized by chronic increase in the defecation
frequency, tenesmus, fetid dark-brown stools with blood streaks and mucus. Histopathology of a colorectal biopsy confirms
the clinical diagnosis, when infiltrates of markedly PAS-positive macrophages are observed in the colonic lamina propria and
submucosa. This communication reports a case of histiocytic ulcerative colitis in a Boxer dog in Brazil.
Case: A Boxer dog, with one year and three months of age had been presenting, since it was nine months old, increased
frequency of defecation, tenesmus, intermittent diarrhea, loose stools with streaks of liquid blood, and coprophagy; however,
no weight loss or appetite loss were noticed. After an initial period of three months experiencing the aforementioned signs, the
dog started with persistent diarrhea with bright red blood, mild prostration, weight loss, and voracious appetite. Because of
continuous deteriorating condition and treatment refractoriness, the dog was euthanized. At necropsy, the colon was decreased
in size with thickened mucosa and foci of ulceration, apart of enlarged mesenteric lymph nodes. Tissue fragments were
collected and fixed in 10% formalin, processed following standard procedures for histopathology, and stained with
Hematoxylin-Eosin (HE). Selected sections from samples of intestines and mesenteric lymph nodes were also stained with
Periodic Acid Shiff (PAS) and Brown-Hopps adapted Gram Staining. Microscopic findings in the colon included infiltration
with rounded to oval bulky macrophages, with eccentric nuclei and abundant eosinophilic and slightly granular cytoplasm.
These macrophages were distributed in the basal lamina propria and submucosa, and there also was diffuse infiltration of
lymphocytes and plasma cells. Extensive multifocal mucosal ulcerations with exposure of the submucosa were also observed.
The cytoplasm of macrophages was strongly marked when stained by Periodic Acid Schiff. Macrófagos do cólon e do
linfonodo mesentérico não coraram pela técnica de Gram.
Discussion: This diagnosis of histiocytic ulcerative colitis was based on the clinical and pathological findings, especially the
association of the clinical signs with the infiltrates of markedly PAS-positive macrophages within the colonic lamina propria
and submucosa, which is considered a typical characteristic of the condition. The disease afflicts mainly young Boxer dogs,
as it was recorded here. In most cases, there is neither weight loss, nor appetite loss, and the hair coat maintains a healthy
appearance. However, in chronic cases such this described here, the dogs may show wasting. Ultrastructural and
immunohistochemical findings in macrophages of HUC have indicated the participation of Escherichia coli in the
etiopathogeny of the disease. The Boxer dog’s predisposition to HUC has been attributed to a hereditary abnormality that
confers invasion and persistence of an adherent E. coli group. This paper reports the importance of the histiocytic ulcerative
colitis as an enteric condition affecting Boxer dogs also in Brazil.
