THE MERCK VETERINARY MANUAL
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Congenital and Inherited Anomalies of the Small and Large Intestine

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Maldigestion or malabsorption disorders usually manifest as chronic, persistent GI signs including vomition, weight loss, small- and/or large-intestinal diarrhea, or a combination of the above. There are many potential etiologies, both heritable and acquired, and most are associated with inflammatory bowel disease (IBD). Congenital conditions may have specific breed predilections.

Soft-coated Wheaten Terriers have a high incidence of concurrent protein-losing enteropathy and nephropathy. Both IBD and food allergies are considered to be a component of this syndrome. The demonstration of elevated fecal α1-protease inhibitor concentrations can help confirm abnormal protein loss through the intestinal tract, although final diagnosis is based on intestinal and renal histopathology. Despite hypoallergenic diet trials and immunosuppressive therapy directed at IBD and glomerulonephritis, prognosis is poor.

Irish Setters are reported to have a familial tendency for a gluten-sensitive enteropathy, with clinical signs beginning as early as 6 mo of age. The wheat sensitivity is both confirmed and treated through the use of gluten-free diets.

Basenjis are prone to an immunoproliferative enteropathy of unknown mode of inheritance; severe lymphocytic-plasmacytic enteritis is a component, and the condition may progress to lymphoma. Diagnosis is based on histopathologic examination of GI biopsies, usually obtained through endoscopy. Treatment trials with immunosuppressive drugs and hypoallergenic diets are usually unsuccessful unless aggressively initiated in the early stages of the disease.

Lymphangiectasia is a malformation of the intestinal lymphatic system that results in a protein-losing enteropathy that may be congenital or acquired, with an increased incidence reported in the Norwegian Lundehunds, Basenjis, Soft-coated Wheaten Terriers, and Yorkshire Terriers. The impaired lymphatic drainage results in dilated lacteals and lymphatics of the intestinal wall. It is diagnosed through the exclusion of other protein-losing diseases and confirmed by histopathology of the small-intestinal wall. Most affected animals respond to a combination of dietary manipulation and anti-inflammatory doses of glucocorticoids. Diets should contain minimal fat with an ample amount of high-quality protein and may be supplemented with medium-chain triglycerides. Additional therapeutics include rutin, a drug that is also effective for chylothorax and lymphedema. Some animals do not respond and succumb to severe protein and caloric malnutrition.

Exocrine pancreatic insufficiency (EPI) has a higher incidence in German Shepherds, Collies, and English Setters and is due to pancreatic acinar atrophy; it is an acquired disease (secondary to pancreatitis) in cats. The lack of pancreatic enzymes results in an osmotic diarrhea, in which steatorrhea is a prominent feature. Affected animals either fail to gain weight or, if EPI is acquired later in life, show a dramatic weight loss. Diagnosis is through the measurement of serum trypsin-like immunoreactivity (TLI); validated tests are available for both dogs and cats. More recent tests include canine pancreatic lipase immunoreactivity, which may be more sensitive for the diagnosis of pancreatitis but does not provide any diagnostic advantage over TLI. Treatment involves the exogenous replacement of pancreatic enzymes and the use of highly digestible diets.

Histiocytic ulcerative colitis is an inflammatory condition thought to be secondary to immune dysregulation involving the colonic histiocytes. It has similarities to Crohn's disease in people. Boxers and French Bulldogs are predisposed, with clinical signs of chronic large-bowel diarrhea beginning in the first year of life. Diagnosis is based on colonic biopsies and response to therapy, including dietary modification and immunosuppressive and/or anti-inflammatory medications.

Ileocolonic agangliosis has been reported in white foals produced by matings of Overo horses to each other. Although the foals appear normal at birth, they soon develop colic and die on the second day. The affected horses are white and have blue irises. Diagnosis can be confirmed by the lack of ganglia in the colon. Congenital defects of the rectum and anus generally result from arrested embryonic development.

Inherited atresias of the small- and large-intestinal tracts are relatively common in large animals. Atresia coli has been reported in Percheron horses and involves the ascending colon at the pelvic flexure. In Swedish Highland cattle, atresia ilei has been recorded, and atresia of the small intestine is seen in lambs. These conditions are invariably fatal. Rectal palpation early in gestation (<45 days) has been implicated as a cause, although recent incidence reduction through selective breeding indicates a potential genetic predisposition as well.

Anal atresia has been reported in sheep, pigs, and cattle; it results when the dorsal membrane separating the rectum and anus fails to rupture. Clinical signs are apparent at birth and include tenesmus, abdominal pain and distention, retention of feces, and the absence of an anal opening. Surgical removal of the membrane is indicated. It is rare in dogs but has been reported in several breeds, including Toy Poodles and Boston Terriers, with an increased incidence in females. Surgical intervention is indicated but may be complicated by postoperative fecal incontinence.

Segmental aplasia (rectal agenesis) is seen when the rectum terminates in a blind pouch before reaching the anus. Surgical correction is difficult because the location of the terminal section varies, and iatrogenic damage to nerves in the area may occur.

Colonic and rectal duplications are rare, and affected animals generally show signs of large-bowel disease. Diagnosis is by contrast colonography. Correction is via surgical removal of the duplication, although some cases have multiple concurrent abdominal developmental anomalies that preclude complete surgical correction.

Rectourethral fistula has been reported in English Bulldogs, cats, and horses and is seen clinically as simultaneous urination from both the urogenital and anal orifices along with a history of chronic urinary tract infections. Diagnosis is via voiding contrast urethrography or retrograde contrast colonography. Surgical correction is curative.

Rectovaginal fistula is a fistulous tract that connects the vagina and rectum and usually is seen in conjunction with imperforate anus. Passage of feces through the vulva or signs of colonic obstruction are suggestive. Diagnosis may be confirmed by barium enema, which outlines the extension of the defect into the vagina. Identification of the fistula, surgical correction, and reestablishment of the normal anatomic structures are imperative. Prognosis is usually guarded. Complications are common and include fecal and urinary incontinence.

Urinary and fecal incontinence is often seen in Manx cats as a sequela of heritable spina bifida.

Last full review/revision March 2012 by Walter Ingwersen, DVM, DVSc, DACVIM

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