23 Intestinal disorders

Diarrhoea

Diarrhoea is defined as a change in the frequency, consistency or volume of bowel movements. Increased frequency may be caused from diseases of the colon or rectum or those that cause larger faecal volume.

In a normal 20 kg dog, 2.5 l of fluids enter the duodenum and over 98% of this is usually reabsorbed. The colon can increase its absorptive capacity three-fold over normal, so the volume of fluid entering the colon must exceed this capacity before diarrhoea is seen. If there is colonic dis­ease, however, only small changes in the absorptive capacity may result in diarrhoea.

Animals with diarrhoea may become faecally incontinent or be unable to retain faeces; however, these two conditions do not necessarily occur concurrently. Animals may be incontinent without diarrhoea or have diarrhoea without incontinence.

Other signs of intestinal disease include the appearance in the stool of bright red blood, melena, mucus and malassimilated nutrients (e.g. steat- orrhoea). Patients may show dyschesia (discomfort on passing stools) or tenesmus (straining to pass stools). Abdominal pain, bloating, increased eructation, borborygmi or flatulence, salivation and anorexia may occur. Intestinal diseases can occur without diarrhoea and should be con­sidered when any of these other signs are present.

Classification of diarrhoea

Diarrhoea is often classified as originating from the large or small in­testine and as acute or chronic (see below) which helps the clinician decide upon the appropriate diagnostic approach.

Osmotic diarrhoea is caused by an increase in unabsorbed solutes in the faeces causing an increase in faecal water content. With the in­creased solutes, water diffuses across the duodenal mucosa and sodi­um diffuses with the water, causing even more water to be drawn into the lumen. Causes of osmotic diarrhoea include overeating, sudden diet changes, gastric dumping (sudden flow of ingesta into the duodenum) or malassimilation. Malassimilation may be due to maldigestion, for ex­ample, with exocrine pancreatic insufficiency or malabsorption such as occurs with small intestinal mucosal or intramural disease. Lactose intol­erance due to lactase deficiency may also cause osmotic diarrhoea due to the unabsorbed lactose in the intestines.

Secretory diarrhoea is due to an increase in the intestinal secretion of fluid greater than the absorption and can occur either due to an in­crease in secretion or a decrease in absorption, or both. Causes of secret­ory diarrhoea include bacterial enterotoxins, deconjugated bile acids, hydroxyl fatty acids, gastrointestinal hormones, cholinergic agonists and enteric system neuropeptides.

Bacteria that can produce enterotoxins include Escherichia coli, Clostridium perfringens, Campylobacter species, Salmonella typhimurium, Staphylococcus aureus, Klebsiella pneumoniae and Yersinia enterocolitica.

Diarrhoea from increased permeability is caused by a defect in the intestinal permeability which causes electrolytes which have been ab­sorbed to flow back into the intestinal lumen. This results in a decrease of absorption of water from the bowel. If the intestinal barrier is further damaged, albumin and other plasma proteins may leak into the intest­inal lumen and with enough damage blood may also be lost.

Deranged intestinal motility may be primary or occur secondarily to oth­er intestinal disorders. A more rapid intestinal transit time can be caused by either decreased segmentation contractions or, much less commonly, increased peristaltic contractions. Decreased segmentation contractions are sometimes termed a garden hose gut, as there is less slowing of the ingesta and less time for absorption. Causes include hookworm infec­tions, canine dysautonomia and some types of colitis.

Diagnosis

Diarrhoea is a clinical sign and not a final diagnosis. In order to treat a patient effectively for diarrhoea, the underlying cause must be found.

Many dogs and cats with acute diarrhoea do not require full investig­ation as their diarrhoea is most likely to be dietary induced and will be self-limiting. These patients receive empiric therapy and frequently im­prove within several days.

Where diarrhoea persists for more than 2 weeks (i.e. is chronic) and is unresponsive to suitable empiric therapy or if there are signs of systemic illness in any patient, they require further investigation.

The approach to investigating patients with chronic diarrhoea should always start with the patient’s signalment, a detailed history and full physical examination.

Young patients are more likely to have nutritional, parasitic or mi­crobial causes of diarrhoea. There are also some breed predispositions to certain types of diarrhoea, for example, exocrine pancreatic insuf­ficiency in young German shepherd dogs. A patient who has been in a boarding kennel or otherwise exposed to new animals has a higher chance of getting an infectious disease.

Assessment should be made of the diet and any changes in the diet and any history of scavenging or hunting or being give treats or snacks or anything other than pet food. Adverse reactions to food are a common cause of diarrhoea and may still occur even when the diet has been fed for a long time. Any change in appetite should be noted, as a poor ap­petite may signify severe disease.

The duration of diarrhoea and the frequency of abnormal or normal appearing stools should be noted, as well as the character of the stools. Many animals will show progressively worsening diarrhoea during the day, as during the night more water is absorbed from the faeces and in­creased activity promotes gastrointestinal (GI) motility. These signs are also important in differentiating small intestinal diarrhoea from large in­testinal diarrhoea (see Table 23.1).

Other questions that should be asked during the history taking in­clude:

• Vaccine history and worming status

• Are there other pets or persons in the household with diarrhoea or has the animal been exposed to other animals (e.g. boarding, playing in the park)?

• Previous history of GI signs

• Presence of vomiting (see section on vomiting for more information)

• Presence of weight loss

As mentioned above, diarrhoea is often classified into small bowel or large bowel disorders. Table 23.1 indicates the parameters which are used to make this distinction.

Table 23.1 Differentiating diarrhoea caused by small bowel disorders from that caused by large bowel disorders

Many patients exhibit symptoms which fall into both categories.

Physical examination

The physical examination should be used to examine the GI tract and to look for evidence of systemic disease. The pet should be assessed un­restrained initially if possible to evaluate attitude and postures. Animals with a painful abdomen may demonstrate a hunched posture (Fig 23.1) and cats with hyperthyroidism may be hyperactive and difficult to ex­amine.

Fig 23.1

Dog showing a hunched posture due to abdominal pain

In particular the clinician should palpate the abdomen for evidence of abnormal intestines, ‘mass’ lesions, pain or fluid/gas accumulations (Fig 23.2). The perineum should be examined for the presence of faeces and for evidence of perineal hernias.

Fig 23.2

Abdominal palpation of a cat

The physical examination is critical for determining the severity of the patient’s disease; warning signs for severe disease include fever, depres­sion, anorexia, weight loss, weakness, dehydration, pale or discoloured mucous membranes and abdominal pain, masses or effusions.

After the history and physical examination it should be possible for the clinician to determine if there is likely to be systemic disease or primary GI disease - if the latter it is likely to be associated with the small or large bowel or both.