Constipation

From Felipedia

Constipation is a significant and sometimes debilitating problem and occurs frequently, especially in the older cat. Owners will present constipated cats complaining of infrequent defecation or difficulty in evacuating faeces (dyschezia or hematochezia). Obviously this is more commonly noticed in the indoor, litter tray-using cat. Chronic constipation may progress to a permanent loss of function, or obstipation, which is generally irreversible. Obstipation implies an inability to evacuate faeces. The natural history of the disease is not completely understood, and it is not safe to assume that all chronically constipated cats end up with permanent inability to defecate^[1].

Megacolon is a descriptive term that is characterized by recurrent constipation and/or obstipation and dilation and hypomotility of the colon.

The colon is sometimes thought of as simply a storage organ with little metabolic function however, the colon serves important physiologic roles, such as the storage of faeces and water absorption. It is also responsible for maintaining an environment for the further digestion of carbohydrates, proteins and dietary fibre by colonic bacteria. This metabolism results in the formation of short chain fatty acids (SCFAs) as well as carbon dioxide, water and methane. SCFAs acidify the luminal environment keeping toxins in an un-ionized (less cytotoxic) form and form precursors for lipid synthesis and gluconeogenesis pathways in the liver that helps to maintain normal gut flora. In most species butyrate acts as a local energy source for the short-lived colonocytes, and the most common source of butyrate is dietary fibre. Soluble fibres such as oats, pectin and vegetable gums produce large quantities of SCFAs. Dysfunction of the colon can lead to illness and debilitation^[2].

Causes

Despite most cases being idiopathic, a significant number of cats suffer constipation secondary to narrowing of the pelvic canal (23%) usually following pelvic fractures, nerve injury (6%) and a small percentage from spinal cord deformity (5%).

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Table 1	Causes of constipation and obstipation
Diet and environment	Ingestion of bones or hair, overgrooming, poor access to litter trays, timidity, boarding catteries, hospitalisation
Painful conditions	Abscess around the tail and anus (cat fight wounds, anal sac abscess), pseudocoprostasis, rectal tumours, Pelvic and tail fractures, abdominal surgery
Metabolic conditions	Dehydration (chronic renal disease), hypokalaemia, hypercalcaemia, hypothyroidism (rare)
Obstruction	Intraluminal – rectal tumours and polyps – rare in the cat
	Extraluminal – pelvic stenosis from previous fractures, intrapelvic tumours
Neuromuscular disease	Dysautonomia, spinal cord trauma or degeneration, idiopathic (common), Manx cat neuropathy, hypoganglionosis
Drugs	Anticholinergic, opioid, diuretics, barium, sucralfate

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Constipation is a common problem that may be worsened intermittently by ingestion of foreign substances such as hair, changes in environment (boarding), metabolic conditions (dehydration) and neurologic disease and occasionally, temporary conditions such as cat fight or anal sac abscesses that might result in painful defaecation. Many cats are presented for unproductive straining sometimes mixed with intermittent bouts of diarrhoea and hematochezia due to the irritant nature of impacted faeces and overgrowth of colonic bacteria. Constipation may lead to illness through dehydration and absorption of bacterial toxins that eventually leads to anorexia, lethargy, weight loss and vomiting.

Clinical signs

Constipation can occur in any breed, age or sex, but is mainly observed in older cats, particularly the Siamese. Some authors believe that male cats are over-represented. Most constipated cats present with difficulty in straining while attempting to defecate. Intermittent vomiting is commonly seen as well. Invariably there is intermittent anorexia, lethargic and distress associated with this disease.

Diagnosis

History taking will often have identified lack of defecation as the primary problem however, in outdoor cats the owner may only notice inappetence, weight loss and possibly vomiting without realising the cat has not defecated for a number of days. In longhaired cats I question owners about flea control and grooming habits of the cat should excessive hair ingestion be worsening the constipation. Changes in diet, particularly the addition of bones should be noted.

Constipation is relatively easy to diagnose on physical examination; the colon is dilated and full of firm faeces. In extreme cases, the colon may be so dilated as to mimic an abdominal mass. Metabolic consequences of constipation such as dehydration should then be excluded by a good physical examination or by evidence on laboratory testing (relative polycythemia, pre-renal azotemia with a concentrated urine and hyperalbuminemia). Hypokalemia and hypercalcemia have been reported to lead to constipation and these should be excluded by evaluating serum biochemistry. Careful attention of the physical examination to the perianal area should identify conditions such as anal sac abscesses, bite wounds, matted fur, masses, herniation or neurologic deficits.

A rectal examination and abdominal and pelvic radiography should be performed on all cases to exclude intra- and extrapelvic abnormalities that may result in narrowing of the pelvic canal and subsequent constipation – this often requires sedation. Rarely, perineal herniation is detected in chronic cases and needs to be addressed surgically. Sometimes abdominal ultrasonography or colonoscopy is indicated if an obstructive intra-pelvic or intraluminal colonic (respectively) mass is suspected. Whilst a number of diseases might be expected to result in constipation (obesity, hypothyroidism) they may only be contributory or coincidental, however they might impact on the short and long-term management of cases so should be considered as part of the diagnostic work up and treatment plan^[3].

Because most constipated cats are older, performing a complete blood count, serum biochemistry profile and urine analysis is often wise to exclude intercurrent diseases.

Treatment

• I/V fluids

Many cats benefit from intravenous fluid therapy to correct for water and electrolyte imbalances before any attempt at manual evacuation. Manual evacuation is a difficult process in the cat and to be done safely requires deep sedation or preferably, general anaesthesia. In severely impacted cats it may be necessary to repeat this process a number of times over several days, and owners need to be forewarned of this. In cats that are severely dehydrated, unwell or that have severely concreted faeces, it is often advisable to rehydrate the cat over 8-12 hours and administer oral laxatives such as lactulose (2-3 mls/kg on initial presentation), which infuses into the stools, and helps soften them before attempting removal. It may also be useful to perform one or two enemas (as below) a number of hours before anaesthesia.

• Enema
• Laxatives

Diet - Laxatives take many forms but increasing non-soluble dietary fibre is often helpful. If the cat is reluctant to eat a high fibre diet (such as Hills W/D) then the owner may wish to add Psyllium husks (1-3 tsp per meal), methylcellulose or bran directly to the food (see Table 2). This often takes some perseverance, as many cats will reject food additives necessitating a gradual introduction to the diet. Obviously these additives are not convenient for cats eating dry diets. Obesity may contribute to constipation so weight control should be part of the management of these cases. Avoiding bones as part of the diet is also important as bone fragments may cause acute impaction.

Coloxyl tablets - given 1-2 times daily

Lactulose - an effective osmotic laxative, which draws fluid into the bowel. Lactulose is usually an adjunct therapy to prokinetic drugs such as cisapride.

• Prokinetics

Prokinetics have become an important part of constipated cat therapy.

Cisapride, a benamide prokinetic agent, acts by increasing gastro-oesophageal sphincter pressure, promoting gastric emptying and enhancing small intestinal and colonic propulsive motility. It is used as doses up to 10mg/kg bid. It has recently been withdrawn from the human pharmacy due to cardiovascular complications. Though these are not reorted in cats, it should probably be used with caution in patients with cardiovascular disease (e.g. Hypertrophic cardiomyopathy). Many compounding pharmacies in Australia (e.g. Compoundia) are able to source and supply cisapride in a convenient capsule form.

Tegaserod is a new potent partial non-benzamide prokinetic. It is used to treat humans with constipation and irritable bowel disorders through its direct simulation of colonic 5-HT4 receptors. Tegaserod has prokinetic effects in the canine colon at doses of 0.03-0.3 mg/kg and also stimulates feline colonic motility in vitro. It is available in Australia as 6mg tablets (Zelmac â , Novartis). Its efficacy in cats is unknown and the author has no personal experience of this drug in cats, however it might be useful in refractory cases and appears to be a safe drug, at least in dogs.

Misoprostol is effective in stimulating feline colonocytes in vitro and may also prove effective in vivo, though reported success in clinical cases of feline megacolon are lacking

In refractory cases, multiple agents may need to be used to control clinical signs.

Colectomy

As most veterinarians are aware, medicating cats with multiple agents can compromise the cat-owner bond. In cats that resist dietary change, tolerate medication poorly, fail to respond to these therapies, or the clinician strongly suspects a diagnosis of megacolon, it is wise to consider surgical colectomy. Megacolon is hard to definitively diagnose, but should be suspected in cats with refractory constipation/obstipation and particularly where the diameter of the colon is greater than 1.5 times the length of lumbar vertebra seven (L7) on lateral abdominal radiography. As these cases are often poorly responsive even to multiple treatments, clients and veterinarians can become frustrated with the poor progress of the case.

The procedure most commonly employed is subtotal colectomy. Although there is some debate over the preservation of the ileocolic junction the general consensus appears to be for preservation as it results in less post-operative diarrhoea. Surgery is well tolerated in most cases although a short period of inappetance following surgery necessitates hospitalisation and fluid therapy. It is important to warn owners that transient diarrhoea following colectomy (4-6 weeks) is not uncommon. Despite subtotal colectomy being a successful treatment in the management of this disease, it is important to consider complications of this surgery which include peritoneal bacterial contamination at the time of surgery, dehiscence of the anastomosis requiring further surgery to correct and rarely, persistent diarrhoea. To enhance success and minimise complications, colonic surgery should only be performed by the experienced or preferably, specialist surgeon^[4].

In cats with hypertrophic megacolon from previous pelvic injuries and subsequent pelvic stenosis improvement may be seen following pelvic osteotomy. Generally, the pelvic stenosis should have been present for less than 6 months for the best success. For those cats with stenosis present for greater than this time, colectomy alone may be curative.

References

1. ↑ White, RN (2002) Surgical management of constipation Journal of Feline Medicine and Surgery 4:129-138
2. ↑ Washabau RJ (2004) Feline constipation, obstipation and megacolon. Proceedings of the Western Veterinary Conference pp:190
3. ↑ Burrows, CF (1996) Constipation, obstipation and megacolon in the cat. Waltham Focus 6:9-14
4. ↑ Washabau RJ & Hasler AH (1997) Constipation, obstipation and megacolon. In: Consulations in Feline Internal Medicine 3, August JR (ed). WB Saunders, Philadelphia pp 104-112