Diagnosis
HUC is accountable for an estimated 14% of cases of colitis that present to an academic hospital over a 20 year period in Australia, but reports in the United States are more conservative, in the region of 2% and on the decline, yet there is an increasing number of reports in the United Kingdom (Churcher and Watson 1997).
The disease has been described typically in Boxers younger than 4-years of age, more commonly female (German et al. 2000; Churcher and Watson 1997), but reports include French bulldog (Gaag et al. 1978; Manchester et al. 2013), Beagle (Carvallo et al. 2015), Mastiff, Alaskan Malamute, Doberman Pincher (Stokes et al. 2001), and Bulldog (Hostutler et al. 2004). There is one case report documenting this condition in a cat (Van Kruiningen and Dobbins 1979). This disease presents much like other causes of chronic colitis - diarrhea characterized by increased frequency of defecation, tenesmus, urgency, hematochezia, and excessive mucus - but in severe cases, weight loss and inappetence can occur (Churcher and Watson 1997).HUC should be considered as an etiology of chronic colitis in a dog with a typical signalment, namely young, usually female, Boxer breed, although other breeds have been diagnosed with this condition. Failure to respond to supportive care, including dietary manipulation, specifically a low residue prescription diet, anthelminthic dosing, and sulfasalazine should prompt an investigation. A minimum database may detect systemic complications including hypoalbuminemia due to protein-losing enteropathy. Differentials diagnoses for the chronic colitis include hypoadrenocorticism, adverse food reaction, dietary allergy or intolerance, parasitic, infectious, neoplastic, motility disorders, strictures, and irritable bowel syndrome. Fecal investigation should include flotation techniques using zinc sulphate fecal flotation for Giardia, and Trichuris spp., PCR for Giardia spp., Salmonella spp., Cryptosporidium spp., and Clostridium perfringes enterotoxin A gene, which can all result in large bowel clinical signs.
The necessity to perform these tests is dictated by the history of the dog's housing environment and diet fed, with high-density housing and a raw meat diet being the greatest risk factors. Rectal scrapes may be helpful in identifying Histoplasma spp. or Pythiosis, although the latter is incredibly challenging to diagnose, often requiring a combination of ultrasound, biopsy, and serology. Ultrasound of the colon wall, examining for layering may be helpful, with transmural thickening and loss of layering indicative of infiltrative neoplasia like lymphoma and Pythium insidiosum. Diagnosis requires endoscopic biopsy after fasting for 48-hours and preparation of the colon with laxatives and enemas.Proctoscopy will reveal inflamed, hypere- mic mucosa in all cases with scattered hemorrhagic foci (Churcher and Watson 1997). The mucosa is also described as being friable and bleeds easily. Confirmation of the diagnosis is made by demonstrating the characteristic histopathology of infiltration by PAS-positive staining macrophages. In addition, special stains to aid in infectious agent identification would include, Gomori methe- namine stain, Gram, and modified Steiner. Fluorescent in situ hybridization (FISH) with a probe against eubacterial 16S rRNA is a sensitive method of detecting bacteria on formalin samples.
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