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. Larger faecal volume is usually due to increased water or nutrients which have not been assimilated and can be affected by the amount of fibre in the diet. Faecal water content increases when there is increased secretion or decreased absorption of fluid. The water content of faeces which appear normal is 60 to 80%; in unformed and watery faeces the water content is 70 to 90%. 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. steatorrhoea). 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. Classification according to pathophysiology also helps in the understanding of the cause of the diarrhoea. The usual pathophysiological classifications include osmotic diarrhoea, secretory diarrhoea, diarrhoea resulting from increased permeability and diarrhoea resulting from deranged motility. More than one of these mechanisms can occur in a patient simultaneously. 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. Causes of increased intestinal permeability include mucosal inflammation, erosion or ulceration, cellular infiltration of the lamina propria (e.g. with neoplastic cells) and compromised blood or lymphatic circulation. Mucosal inflammation is present in chronic inflammatory bowel disease, gluten enteropathy and milk protein intolerance. 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. 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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. Larger faecal volume is usually due to increased water or nutrients which have not been assimilated and can be affected by the amount of fibre in the diet. Faecal water content increases when there is increased secretion or decreased absorption of fluid. The water content of faeces which appear normal is 60 to 80%; in unformed and watery faeces the water content is 70 to 90%. 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. steatorrhoea). 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. Classification according to pathophysiology also helps in the understanding of the cause of the diarrhoea. The usual pathophysiological classifications include osmotic diarrhoea, secretory diarrhoea, diarrhoea resulting from increased permeability and diarrhoea resulting from deranged motility. More than one of these mechanisms can occur in a patient simultaneously. 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. Causes of increased intestinal permeability include mucosal inflammation, erosion or ulceration, cellular infiltration of the lamina propria (e.g. with neoplastic cells) and compromised blood or lymphatic circulation. Mucosal inflammation is present in chronic inflammatory bowel disease, gluten enteropathy and milk protein intolerance. 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. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Oesophageal stricture in a cat Vomiting Ingestion of glue by a dog Pancreatitis in a cat Stay updated, free articles. Join our Telegram channel Join
