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Constipation in the dog and cat. Diagnostic and therapeutic approach

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Category: Schede
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  • Disciplina: Gastroenterologia
  • Specie: Cane e Gatto

Constipation, defined as decreased or difficult evacuation of faeces, is a problem more frequently encountered in the cat than in the dog. The term constipation is not always indicative of loss of colonic function; it is only when constipation is uncontrollable and unresponsive to therapy that obstipation is present, meaning a severe and complete constipation with permanent loss of function. Persistent constipation (obstipation) may be the cause of colonic dilation and hypertrophy, a conditiondefined by the term megacolon; this represents the final stage of a colonic abnormality idiopathic in nature. 

 

EPIDEMIOLOGY AND CLINICAL SIGNS

Although constipation, obstipation or megacolon may affect animals of most breeds and ages, the majority of affected animals are middle-aged cats, especially male European short-haired cats.1

Animals are usuallybrought to the veterinarian because they haven’t been able to defecate for several days or weeks. Owners often report unsuccessful attempts to defecate by their dog or cat. The stools produced are usually extremely dry. Animals that remain constipated for long periods of time may develop diarrhoea, because of the irritating effect that faecal secretions may have on the mucosa; diarrhoea may at times be the only clinical sign present. Other possible signs of constipation are anorexia, vomiting and weight loss.

In most cases the physical examination reveals the presence of a faecaloma. Patients are typically dehydrated, with weight loss and abdominal pain. In dysautonomic cats, a condition predisposing to faecalomas, other clinical signs are also present, such as mydriasis, prolapse of the third eyelid, reduced lacrimation, megaoesophagus, bradycardia and others.Rectal examination is very important as it can reveal several causes of constipation, such as the presence of foreign bodies, diverticula, stenosis, inflammation or perineal hernia. A neurological examination should always be performed in addition to the physical examination, so as to rule out neurological problems such as spinal cord injury, pelvic nerve trauma as well as other disorders.

 

PATHOGENESIS

The pathogenesis of constipation has been attributed to the presence of either a neurogenic disorder or of an underlying degenerative neuromuscular disease. These two hypotheses are true only in a small percentage of cases as the majority of patients with constipation suffer in fact from the presence of colonic smooth-muscle disorders.2 Studies performed by Washabau etal.3, 4have shown that in the cat, idiopathic megacolon is caused by a generalized colonic smooth-muscle dysfunction and that targeted treatments to stimulate muscle contraction may improve motility.

In affected cases, colonichistology is often normal; the lesion probably starts in the descending colon and then, with time, it may also extend to the ascending colon.

 

DIAGNOSIS

In the presence of constipation the complete blood count, biochemical profile and urinalysis are usually normal but may at times reveal the presence of metabolic causes, such as dehydration or electrolyte abnormalities (e.g., hypokalemia, hypercalcemia, etc.). In young animals, especially in cats with frequent episodes of constipation and with other signs compatible with hypothyroidism, thyroid function tests should be performed.

Abdominal radiographs are necessary to assess the extent of the problem and to search for possible causes; they can also be helpful in identifying possible predisposing factors, such as pelvic fractures, extra-luminal masses, foreign bodies, etc. Other tests that may be useful are abdominal ultrasound, endoscopy (withbiopsies) as well as barium x-rays. Both in the case of colonoscopy and in the execution of an enema the colon must be cleared of stools before testing. In animals with neurological signs, cerebrospinal fluid analysis and other neurological examinations may be necessary.

 

TREATMENT

In treating patients with megacolon it is very important to restore and maintain hydration, while the hardened stools should be removed. Medical treatment consists of three steps:

  • administrationof dietary fibre in cases of mild constipation;
  • use oflaxatives and prokinetics in cases of moderate or recurrent constipation;
  • surgeryin cases of persistent constipation and megacolon.

Dehydration

In dehydrated patients,the first step consists in rehydration. This can be done with parenteral fluid therapy - subcutaneously at home -, with the use of wet-food diets (cans), adding water or stock to the food or using water fountains. The addition of dietary fibre should be avoided until the patient is properly rehydrated.

Removal of hardened stools

Removal of the hardened faecal material is necessary in order to reduce the toxic and inflammatory stress on the bowel wall. For this purpose, paediatric suppositories that work well in cases of mild constipation can be used, such as dioctyl sodium sulfosuccinate, glycerol and bisacodyl. The use of suppositories requires a collaborative animal and a very motivated owner; they can be used alone or in combination with oral laxatives.

Enemas are another easy way to soften the hardened stools. Solutions that may be used for this purpose include hot tap water, dioctyl sodium sulfosuccinate (5-10 ml/cat), mineral oil (5-10 ml/cat) or lactulose (5-10 ml/cat). Enemas should be administered slowly, through a well-lubricated rubber tube, in order to prevent muscle damage and vomiting. Mineral oil should not be used together with dioctyl sodium sulfosuccinate, as the latter can promote the absorption of the mineral oil by the intestinal mucosa. In the cat, enemas containing sodium phosphate should not be used, as they may predispose the patient to life-threatening electrolyte imbalances (hypernatremia, hyperphosphatemia and hypocalcemia).

In some patients, manual extraction of the faecesmay be necessary. In such cases it is first necessary to administer an enema, perform a colonic massage and then finally manually reduce the faecal mass with great caution, in order to diminish the risk of perforation. Whenever a cat is anaesthetized for colonic manipulation it should first be intubated, so as to prevent aspiration of gastric secretions in case of vomiting.

Use of dietary fibre

Dietary fibres act as a laxative. There are two types of fibre - soluble and insoluble. Insoluble fibres (wheat bran, cereals, psyllium, etc.) can improve or normalize colonic motility: they increase the water content in the bowel segment, hence diluting luminal toxins (such as bile acids, ammonia and ingested toxins) and reducing colonocyte exposure to toxins by increasing bowel movement frequency. The recommended doses are: psyllium (Metamucil, 1-4 teaspoons mixed with food PO q 12-24 h); durum wheat bran (1-2 tablespoons mixed with food PO q 24 h).

Soluble fibres (highly fermentable), which include oat bran, pectin, beet pulp, vegetable gums, etc., are easily digested by gastrointestinal bacteria; they thus provide large amounts of short chain fatty acids, which are useful for colonic health but are not suitable as a laxative in view of their reduced water-drawing capacity and hence inability to dilute endoluminal toxins.

Laxatives

Laxatives can be classified according to their mechanism of action: emollients, lubricants, hyperosmotics and stimulants.

Emollient laxatives are anionic detergents that increase the miscibility of water and lipids in the faeces; they improve the absorption of lipids and reduce the absorption of water. Dioctyl sodium sulfosuccinate and dioctyl calcium sulfosuccinate are examples of emollient laxatives that may be used in the cat. Also in this case, before using such products the animal must first be well hydrated. It is important to note that the efficacy of these products has been proven in vitro but not in vivo, and in our patients it is likely that these products may not reach concentrations sufficient to facilitate the expulsion of faeces.

Lubricant laxatives may prevent colonic water absorption and thus facilitate the passage of stools. Mineral oil (10-25 ml PO q 24 hours) or petroleum jelly (1-5 ml PO q 24 hours) are more indicated in cases of mild constipation. Mineral oil is most effective when administered rectally by enema rather than by the oral route; this also reduces the risk of aspiration pneumonia. When lubricant laxatives are used chronically, they can interfere with the absorption of fat-soluble vitamins and lead to vitamin deficiencies.

Hyperosmotic laxatives may stimulate the secretion of fluids in the intestinal lumen and induce colonic propulsive motility. Three types of hyperosmotic laxatives are available: poorly absorbed polysaccharides (such as lactulose and lactose), magnesium salts (magnesium citrate, magnesium sulfate, magnesium hydroxide) and polyethylene glycols. Lactulose (0.5 mg/kg PO q 8-12 hours) is the most effective and perhaps the safest agent in this group; in the presence of flatulence and diarrhoea the dose should be reduced. Magnesium salts and polyethylene glycols are currently contraindicated in the cat, and even more so in patients with renal failure or with functional or mechanical bowel obstruction. 

Stimulant laxatives may improve colonic propulsive motility through various modes of action. Bisacodyl (5 mg PO q 24 hours) is very effective in the cat; it acts by stimulating epithelial secretion through the production of nitric oxide and the depolarization of myenteric plexus neurons. If these products are used chronically they can cause damage to the myenteric plexus.

Prokinetics

Prokinetics are a relatively new class of drugs with the ability to stimulate smooth-muscle motility. The best known of these agents is cisapride, which, anecdotally, may be useful in cases of mild-to-moderate constipation;3-6 the doses used range from 0.1-5 mg PO q 8-12 hours, with no known adverse events.  For the time being the efficacy of this drug has been shown only in vitro and no certainties exist about its efficacy in vivo. Signs of acute toxicosis in the dog include diarrhoea, dyspnoea, tremors, seizures and others. In recent years, in various countries, cisapride has been withdrawn from the pharmaceutical market due to problems of cardiac toxicity exhibited in a small group of human patients; cisapride is therefore not readily available on the market.

A study by Washabau and Hall5 demonstrated that nizatidine and ranitidine can stimulate colonic smooth-muscles, in vitro; these seem to work through inhibition of acetylcholinesterase. The suggested doses, also in combination with cisapride, are: for ranitidine, 1-2 mg/kg PO q 12 hours; for nizatidine, 2.5-5.0 mg/kg PO q 12 hours. Erythromycin and motilin may be effective in increasing intestinal motility in the dog, but they do not seem to be effective in the colon of the cat. Other, more recent prokinetic drugs are now available, but they are not yet widely used. Prucalopride, at the dose of 0.64 mg/kg in the cat, may increase bowel movements within the first hour after its administration. Misoprostol has been recently shown to be able to stimulate smooth-muscle contractions in the cat, in vitro.

Surgery

Cats with chronic constipation or megacolon are good candidates for colectomy.7-9 Chronic faecal impaction can cause local inflammation and mucosal ulcerations, with risk of perforation. Surgery should be performed before the intestinal wall and the health of the patient are compromised. The harvesting of small intestinal biopsies is recommended at the time of resection, to rule out diseases such as lymphosarcoma, feline infectious peritonitis, and others. The prognosis is favourable, but in the postoperative period patients may often present diarrhoea for about 4-6 weeks and at times even constipation.10

In the presence of hypertrophic megacolon, pelvic osteotomy may be necessary in addition to colectomy. If megacolon has been present for less than six months, following a pelvic fracture, colectomy may not be necessary.11 Hypertrophic megacolon may be entirely reversible with pelvic osteotomy alone; colectomy is however necessary in cats with signs of colon hypertrophy present for more than 6 monts.11, 12 The hypertrophy is considered secondary to neuromuscular degeneration and to pathological dilatation; in such cases osteotomy alone may not be sufficient. Very interesting, however, is the fact that these animals can often improve with colectomy alone.

In summary, in the presence of constipation, if possible, the underlying causes should be removed; the animal should be kept well hydrated; medications should be administered to help faecal expulsion and prevent faecal impaction; surgery should be considered in the presence of recurrent episodes of constipation or megacolon.

 

Bibliography

  1. Washabau RJ, Hasler AH. Constipation, obstipation, and megacolon. In: August J, ed. Consultations in feline internal medicine, ed 3. Philadelphia: Saunders 1997.
  2. Washabau RJ, Stalis IH. Alterations in colonic smooth-muscle function in cats with idiopathic megacolon. Am J Vet Res 1996;57(4):580-587.
  3. Hasler AH, Washabau RJ. Cisapride stimulates contraction of idiopathic megacolonic smooth muscle in cats. J Vet Intern Med 1997;11(6):313-318.
  4. Washabau RJ, Holt D. Pathogenesis, diagnosis, and therapy of feline idiopathic megacolon. Vet Clin North Am Small Anim Pract 1999;29(2):589-603.
  5. Hall JA, Washabau RJ. Diagnosis and treatment of gastric motility disorders. Vet Clin North Am Small Anim Pract 1999 Mar;29(2):377-95.
  6. Washabau RJ, Sammarco J. Effect of cisapride on feline colonic smooth muscle function. Am J Vet Res 1996;57:541.
  7. Gregory CR et al. Enteric function in cats after subtotal colectomy for treatment of megacolon. Vet Surg 1990; 19(3):216-220.
  8. Kudisch M, Pavletic MM. Subtotal colectomy with surgical stapling instruments via a trans-cecal approach for treatment of acquired megacolon in cats. Vet Surg 1993;22(6):457-463.
  9. Rosin E. Megacolon in cats: the role of colectomy. Vet Clin North Am Small Anim Pract 1993;23(3):587-594.
  10. Sweet DC, Hardie EM et al. Preservation versus excision of the ileocolic junction during colectomy for megacolon. A study of 22 cats. JSAP 1994;35:358.
  11. Schrader SC. Pelvic osteotomy as treatment for constipation in cats with acquired stenosis of the pelvic canal. JAVMA 1992;200:208.
  12. Matthiesen DT, Scavelli TD et al. Subtotal colectomy for treatment of obstipation secondary to pelvic fracture malunion in cats. Vet Surg 1991;20:113.