Irritable bowel syndrome

Irritable bowel syndrome (IBS) is a commonly diagnosed, but poorly understood functional disorder in dogs.² Other terms used to describe this syndrome include spastic colon, nervous colitis, and mucus colitis.²⁵ It has been estimated that 10-15% of dogs with chronic large bowel diarrhea have IBS.²⁶ Ap­proximately 15% of human adults in the United States report symptoms consistent with a diagnosis of IBS.²⁷ IBS is defined by colonic dysfunction in the absence of identifiable struc­tural, biochemical, or microbiological abnormalities.

In dogs, IBS is a diagnosis of exclusion and known causes of large bowel diarrhea must be eliminated before a diagnosis of IBS can be made. It is possible that dogs diagnosed with IBS:

1) may truly have a syndrome similar to IBS in human beings,

2) may have another colonic disorder that has not been cor­rectly diagnosed, or 3) may have one of several newly de­scribed conditions, such as fiber-responsive large bowel di­arrhea or Clostridium pefringens enterotoxicosis.

Pathophysiology

There have been no pathophysiological studies concerning IBS in dogs. Studies in human beings have investigated the role of low fiber diets, food allergy or intolerance, abnormal GI motility, altered pain and visceral perception, psychosocial factors, and an imbalance of GI neurotransmitters.²⁷ Abnormal myoelectrical activity leads to abnormal intestinal motility, which is likely the ultimate cause of the clinical signs.²⁵

Clinical signs

In dogs, the most common clinical sign of IBS is intermittent large bowel diarrhea with excess fecal mucus, tenesmus, ur­gency to defecate, and increased frequency of defecation.²⁵ Intermittent bloating, nausea, vomiting, and abdominal pain may also occur, but hematochezia is uncommon.

with the development of cyclic clinical signs. Affected dogs may be hyperexcitable, unmanageable, or possess abnormal personality traits. However, dogs without these abnormalities can also develop IBS.²⁶

Diagnosis

It cannot be overemphasized that IBS in dogs is a diagnosis of exclusion. A thorough diagnostic plan must be followed before a diagnosis of IBS can be made. Fecal examinations must be negative for parasite infestations and laboratory evaluation should eliminate the possibility of any systemic disorder. Also a dietary trial with a highly digestible low-fat diet and de­worming against whipworms should be instituted before making a diagnosis of IBS. Finally, colonoscopic examination and mucosal biopsy must be normal (Figure 6.9). In some cases of IBS, spasm of the colonic wall may occur after contact with the endoscope. In the author’s experience, response to a high fiber diet does not eliminate the presence of IBS, but it may support a diagnosis of fiber-responsive large bowel di­arrhea instead. The potential relationship between IBS and fiber-responsive large bowel diarrhea will be discussed in the next section.

Treatment

The intermittent nature of clinical signs often makes assess­ment of IBS therapy difficult. Multiple treatments often need to be tried before a control of the clinical signs is achieved. If a stress factor or abnormal personality trait can be identified, behavioral modification can be beneficial. Unfortunately, many stressors cannot be eliminated, and many clients are un­able or unwilling to alter their own behavior or attempt to alter their pet’s behavior. Thus, dietary and pharmacological therapy is commonly utilized. The author has recommended supplementing highly digestible diets with a source of soluble fiber. In many cases, feeding high fiber diets can lead to a re­duction in dosages and frequency of administration of phar­macological agents required or may totally eliminate the need for drug therapy.

The severity and frequency of diarrhea can also be reduced by motility modifying agents, such as loperamide or diphenoxy­late. These drugs reduce diarrhea by increasing colonic seg­mentation. They can often be given for several days and dis­continued after the diarrhea resolves.²⁵ Pain can often be relieved by antispasmodic agents and the effects of stressors can be reduced by sedatives. Librax^® contains the sedative chlor­diazepoxide (5 mg) and clidinium bromide (2.5 mg), an anti­cholinergic agent. A suggested dosage is 0.1-0.25 mg/kg of clidinium or 1-2 capsules of Librax® PO q 8-12 h.^25,28 The drug can be given when the owner first notices abdominal pain or diarrhea, or when stressful conditions are anticipated or encountered, and can usually be discontinued after a few days. Other anticholinergics such as propantheline (Pro-Ban- thine®) at 0.25 mg/kg PO q 8-12 h, hyoscyamine (Levsin®) at 0.003-0.006 mg/kg PO q 8-12 h, or dicyclomine (Bentyl®) at 0.15 mg/kg PO q 8-12 h have also been suggested.^2,25 An­ticholinergics can decrease or inhibit GI motility, which may worsen the diarrhea. Other side-effects are uncommon. In hu­man patients with IBS, the side effects include xerostomia, urinary retention, blurred vision, headache, psychosis, nerv­ousness, and drowsiness. On occasion, nausea and vomiting prevent the administration of oral medications. Parenteral an­tiemetics can be given to relieve nausea and vomiting and al­low administration of oral medications 1-2 days later.²⁵

Prognosis

The prognosis for a cure of IBS in dogs is guarded. Affected dogs may have intermittent clinical signs for years. Environ­mental, dietary, and pharmacological therapy often results in control or a reduction of clinical signs. Those dogs that re­spond to fiber supplementation have a good prognosis for re­duction or elimination of their clinical signs (see next sec­tion).

6.3.6