Congenital and Inherited Anomalies of the Small and Large Intestine
Maldigestion or malabsorption disorders usually manifest as chronic, persistent GI signs, including vomiting, 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 protein-losing enteropathy (PLE), which may be seen alone or in association with protein-losing nephropathy (PLN). Although the mode of inheritance is not clear, the etiopathogenesis of PLN is likely different than that of PLE, due to podocytopathy. Dogs with PLE have both food hypersensitivities and IBD, although the pathogenesis is not clear. The demonstration of increased fecal α1-protease inhibitor concentrations can help confirm abnormal protein loss through the intestinal tract, although this is more useful as a screening test in animals <3 yr old. A definitive diagnosis is based on intestinal and renal histopathology. Despite hypoallergenic diet trials and immunosuppressive therapy directed at IBD and/or glomerulonephritis, prognosis is poor.
Gluten-sensitive enteropathy has been shown to be inherited by an autosomal recessive manner in Irish Setters. However, the pathogenesis in dogs appears to be different than that of celiac disease in people. One case has also been described in a horse. The wheat sensitivity is both confirmed and treated through use of gluten-free diets.
Basenjis have been diagnosed as carriers of a severe form of lymphocytic-plasmacytic enteritis called Basenji enteropathy, although the mode of inheritance is not known. The stomach may also be affected. Clinical signs include diarrhea and weight loss, with hyperglobulinemia. 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 early in 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 a 50% incidence in Norwegian Lundehunds in the USA. Other affected breeds include Yorkshire Terriers, Maltese, Rottweilers, and Shar-Pei. Lymph vessels become dilated, secreting lymph into the intestines, which results in hypoproteinemia, lymphopenia, and lipogranulomatous inflammation of surrounding tissues. It is diagnosed through 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, be energy dense, and easily digestible. Although remission of clinical signs may be achieved, the longterm outcome is usually poor.
Exocrine pancreatic insufficiency (EPI) has a higher incidence in German Shepherds and Rough Collies, although it has been diagnosed in many breeds. Disease is due to pancreatic acinar atrophy, which is due to immune-mediated destruction and infiltration of lymphocytes. In German Shepherds and Pembroke Welsh Corgis, genome-wide association studies have identified several major histocompatibility complex haplotypes associated with EPI in affected animals, suggesting a complex mode of inheritance. 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 measurement of serum trypsin-like immunoreactivity; validated tests are available for both dogs and cats. Treatment involves exogenous replacement of pancreatic enzymes and use of highly digestible diets.
Granulomatous colitis, previously called histiocytic ulcerative colitis, has been diagnosed in Boxers and French Bulldogs, with sporadic cases in a few other breeds. The disease is characterized by granulomatous inflammation of the colonic mucosa in association with infection with adherent and invasive Escherichia coli. An autosomal recessive defect in the immune system that predisposes to E coli infection is suspected. Clinical signs arise in animals <4 yr old and include diarrhea, hematochezia, tenesmus, and weight loss. Diagnosis is by histologic examination of colonic mucosal biopsies. Successful remission has been achieved in animals treated with enrofloxacin; however, treatment has been unsuccessful in cases in which the E coli was resistant to fluoroquinolones.
Ileocolonic agangliosis, or overo lethal white syndrome, occurs in white foals with blue eyes produced by Overo-Overo matings. The condition is fatal. It is due to mutation in the endothelin B receptor and is inherited in an autosomal recessive manner. Although the foals appear normal at birth, they rapidly develop signs of colic and meconium impaction due to hypoinnervation of the intestinal tract, which causes lack of motility. Diagnosis can be confirmed at necropsy by the lack of ganglia in the colon. Adult Overo horses can be screened for genetic status before breeding to reduce incidence. Congenital atresias of either the small- or large-intestinal tracts have been described in most domesticated animal species. Atresia coli has been reported in several foals of differing breeds. Atresia ilei in Swedish Highland cattle, and atresia jejunae in Jersey cattle are likely due to autosomal recessive inheritance. These conditions are invariably fatal. Aggressive manipulation of the bovine conceptus by transrectal palpation early in gestation (<45 days) has been implicated as a cause, although a reduction in incidence through selective breeding indicates a potential genetic predisposition as well.
Atresia ani 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 absence of an anal opening. It is rare in dogs but has been reported in several breeds, including Toy Poodles and Boston Terriers, with an increased incidence in females. Concurrent rectovaginal fistula may occur. Euthanasia is recommended in large animals. In small animals, postoperative fecal incontinence may be a complication of surgical intervention.
Segmental aplasia of the rectum (rectal atresia) 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.
Enteric duplications are very rare, with only a few cases described in several species, and may include the colon or rectum. Duplications may communicate with the lumen of the patent tract or be separate (duplication cyst). Affected animals may be diagnosed by identification of an abdominal mass, or they may show GI signs. Diagnosis is by ultrasonography or contrast CT. 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 primarily in English Bulldogs and is diagnosed clinically as simultaneous urination from both the urogenital and anal orifices along with a history of chronic urinary tract infections. Diagnosis is via cystourethroscopy with concurrent colorectal infusion of contrast material, or by contrast CT. 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 is suggestive. Diagnosis may be confirmed by barium enema, which outlines the extension of the defect into the vagina, or video endoscopy. 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.