FECAL INCONTINENCE

Fecal incontinence denotes uncontrolled release of rectal contents. Although it is not a common dis­order in dogs and only rarely occurs in cats, the ramifications of this problem for a household pet and its owner are highly significant.

There are many potential causes of fecal incon­tinence (Box 1-12). Most incontinence disorders can be classified as neurogenic or nonneurogenic. Causes include anatomic disruption of the anal sphincters or pudendal nerve trauma resulting from surgery (e.g., perineal hernia repair, perianal fistula repair, anal sac removal, tumor removal), obstetric trauma or other injuries (e.g., lacerations, bite wound trauma with subsequent ascending bacterial neuritis as may occur from a cat fight injury), and various non—surgery-related neuro­logic problems. Neurologic problems may include peripheral neuropathies, cauda equina syndrome, and congenital defects of the caudal vertebral col­umn and spinal cord (e.g., sacrocaudal agenesis of Manx cats). Incontinence may be related to aging in some patients. Also, any disease that causes rapid transit of large volumes of diarrhea (e.g., severe enteritis) may produce transient fecal incontinence in patients with healthy continence mechanisms.

The mechanisms of anal continence are com­plex, and a detailed description is beyond the scope of this discussion. In the dog and cat the internal and external anal sphincter muscles and the puborectalis muscle (the caudal portion of the levator ani muscle) play major roles in maintaining continence. The most important muscle in main­taining the sphincter component of the conti­nence mechanism may be the puborectalis muscle.

nerve (afferent and efferent) and pudendal and hypogastric nerves (efferent).

The colon also plays an important role in help­ing to maintain fecal continence through its reservoir function. Reflex activity in the colon appears to allow the external anal sphincter to retain fecal material while the internal anal sphincter relaxes, thereby allowing the colon to dilate and accommodate increases in fecal mass. Simultaneously there is a brief (several minutes) decrease in propulsive contractions in the colon, which also helps facilitate the accommodation process. The colon continues to readapt with sub­sequent peristaltic delivery of fecal material until a time when defecation is appropriate. If the colon is presented with large volumes of watery fecal material in a short period of time, as may occur in patients with severe viral or bacterial enteritis, this reservoir function can become overwhelmed and transient incontinence (urge incontinence) may result. Urge incontinence can also be associated with moderate to severe proctitis or colitis, in which the patient experiences significant discom­fort (perhaps a “burning” sensation) with a result­ant sense of urgency to defecate and overriding of the continence mechanism.

The internal and external anal sphincter mus­cles and the puborectalis muscle are primarily responsible for maintaining a high-pressure zone in the terminal rectum that maintains continence at rest.

Diagnosis

Important factors in diagnosis include obtaining a detailed history so that any potential causative fac­tors (e.g., trauma, difficult whelping, history of sig­nificant constipation problems) can be elucidated, physical examination (including neurologic assess­ment), and completion of any indicated diagnostic tests.

The signalment is very important in evaluating a patient with fecal incontinence. Manx and other tailless cats and Old English sheepdogs, bulldogs, and Boston terriers may be affected with an agen­esis of the sacrocaudal vertebrae and spinal cord. The neurologic deficit is present from birth but is often first noted at weaning. Clinical signs include both urinary and fecal soiling and irrita­tion around the perineal and abdominal skin. Occasionally there is complete paralysis of the pelvic limbs as well. Aging patients with gradual onset of incontinence are most likely to have some type of neurologic problem.

Once the existence of incontinence has been established, the clinical evaluation begins with an assessment of the frequency, severity, and circum­stances surrounding the incontinent episodes. How acute are the symptoms? Are the episodes associated with urgency, or is there no prior warn­ing? The owner should be asked whether or not the dog still assumes an appropriate posture for defecation, and, if so, does this take place at an appropriate time and place? Some dogs with mild incontinence still do this on a fairly routine basis but on occasion will inappropriately release stool when asleep, during periods of relaxation, or while on a walk. These episodes may occur in response to increased rectal pressure related to the presence of stool that overrides a now compromised conti­nence mechanism.

Excitement may also cause spontaneous evacua­tion of stool. In some patients incontinence episodes become much more frequent (i.e., major incontinence versus partial), and this suggests a severe anorectal sensory disorder. Unconscious anal dribbling of small amounts of fluid and residue may become common, especially during periods of increased abdominal or rectal pressure (e.g., associ­ated with coughing, excitement, or exercise).

The owner should also be asked if the patient can urinate normally. Because micturition relies on nerve pathways similar to those involved in fecal continence, abnormalities involving both functions suggest that the fecal incontinence is of neurologic origin.

If the fecal incontinence has been a very recent development, questions regarding trauma are asked. Lumbosacral and sacrocaudal fracture, sub­luxation, and luxation can cause fecal inconti­nence (distended bladder and atonic tail often result as well). In cats these injuries are commonly associated with getting their tails caught by some­thing. Cats with bite wounds around the tailhead may develop abscessation and ascending bacterial neuritis and meningomyelitis of the caudal spinal cord. Any history of anorectal surgery is reviewed. Generally symptoms develop and are reported shortly after any surgery in which nerve damage occurs. Any incidence of significant straining episodes should also be discussed. Severe proctitis, for example, may cause so much irritation that urge incontinence occurs.

In my experience one of the most common presentations for the complaint of fecal incon­tinence is an aging dog with no obvious predis­posing history of major trauma, anorectal disease, or neurologic disease. Careful studies using electromyography and other neurophysiologic techniques in human patients with “idiopathic” incontinence have identified striated muscle denervation damage in the majority. Detailed studies have not been done in animals, but it is suspected that a similar mechanism exists.

Physical Examination

The most important aspects of the physical examination in a patient with fecal incontinence include close perianal inspection and digital examination of the anorectum. The skin in the perianal and perineal regions may show evidence of irritation from fecal or urinary soiling. Perianal fistulas, which may be accompanied by mild leak­age of residue from the rectum, are readily iden­tified on visual inspection. Rectal examination may reveal evidence of proctitis (e.g., increased sensitivity on palpation, irregular rectal mucosa) or a perineal hernia. Fecal incontinence has been documented as a potential complication of per­ineal herniation, most likely occurring secondary to external anal sphincter incompetence. Anal tone is assessed during digital palpation, but it should be noted that this provides only a crude assessment (unless there is loss of tone altogether) of true anal sphincter function. The presence of fecal impaction and tumors can also be deter­mined. Abdominal palpation is done to assess blad­der tone (a large, distended, easily expressed bladder found in conjunction with fecal inconti­nence and a dilated anus supports diagnosis of a neurogenic disorder), colon content, and any sensitivity of the colon that might suggest coli­tis. Signs of hindlimb paresthesia and hyperes­thesia suggest the possibility of cauda equina syndrome.

Neurologic examination includes evaluation of gait, pelvic limb postural reactions and proprio­ception, and spinal reflexes of the pelvic limbs, anus, tail, and bladder. The anal reflex is elicited by pinching or touching the anus and observing con­tracture of the anal sphincter. If the S1 to S3 spinal segments or nerve roots are damaged, the anus is dilated and unresponsive.

Diagnostic Testing

Baseline analysis of patients with fecal inconti­nence without a readily explainable cause includes survey radiography of the lumbar spine and lumbosacral and tailhead areas and proctoscopy with examination and biopsy of the rectum and colon.

Treatment

The treatment of fecal incontinence is directed toward the underlying cause if one can be identi­fied. The prognosis for resolution or adequate con­trol of incontinence also varies with the type and extent of involvement, but, in general, it is some­what worse when neurogenic disorders (especially those resulting from surgical damage) are present.

General treatment principles include dietary manipulation, pharmacologic therapy to increase anal tone and decrease colonic transit rate (opiate derivatives), and proper supportive care for any injuries that may have been incurred.

The goal of dietary therapy is to minimize fecal volume. This is best accomplished through feeding a low-residue, highly digestible diet. Homemade diets consisting of cottage cheese and rice or tofu and rice often work well. Commercial diets such as Eukanuba Low-Residue (Iams), IVD Select Care Sensitive and Canine Vegetarian Formula diets, or Prescription Diet Canine i/d (Hill's) may also be effective. Two to three small meals rather than one large meal should be fed each day.

When fecal incontinence is associated with chronic diarrhea, urgency, or decreased anal tone as may be seen in aging patients, symptomatic improvement can often be effected with opiate derivatives (diphenoxylate [Lomotil], loperamide [Imodium]). Solid stools are much easier to retain than liquid stools, and thus antidiarrheal therapy alone may eliminate all symptoms in patients with loose stools. Several human studies have suggested that loperamide is superior to diphenoxylate in reducing soiling and improving continence of rec­tally infused saline. Pharmacologic actions include increased anal tone, increased fluid absorption in the colon, decreased secretions, and increased rhythmic segmentation in the bowel, thereby decreasing colonic transit rate. These drugs can be safely administered on a long-term basis if neces­sary. I have had good success in managing geriatric patients with age-related incontinence with low- residue diets used in conjunction with loperamide. Dosage recommendations for these drugs are pre­sented in Chapter 8. It may also be useful to man­age geriatric patients with incontinence problems with periodic enemas in an effort to decrease fecal volume in the rectum and colon, as well as to help decrease episodes of fecal soiling.

Inflammatory disorders (colitis, proctitis, anusi- tis) are treated with antiinflammatory medications used either singly or in combination. The most commonly used drugs include sulfasalazine (Azulfidine), metronidazole (Flagyl), and pred­nisone. Use of these drugs for large bowel disor­ders is discussed in detail in Chapter 8. Loperamide or diphenoxylate may be used in con­junction with any of these drugs as well. Dietary therapy in the form of a highly digestible low- residue diet, as discussed previously, is also used.

Surgical intervention is indicated for patients with incontinence related to perineal herniation or anal or rectal neoplasia and for some with dis­eases of the lumbosacral spine. The prognosis is guarded when profound urinary and anal sphinc­ter disturbances exist. Attempts have been made to correct complete neurogenic fecal incontinence surgically with such techniques as fascia slings or silicone elastomer slings. However, results have not been encouraging, and these procedures are not commonly recommended.