Constipation in cats                                    See also Megacolon

© Foster, D. The Management of Constipated cats. The Veterinarian Oct 2006 pp35-39 http://www.theveterinarian.com.au/clinicalreview/article757.asp

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). 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. Megacolon is a descriptive term that is characterized by recurrent constipation and/or obstipation and dilation and hypomotility if the colon (White, 2002). Two forms of megacolon occur – the idiopathic form where there is an irreversible loss of function and the hypertrophic form that is secondary to other conditions such as a narrowed pelvic canal. The hypertrophic form may reverse if the underlying cause is reversed early enough.

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. 

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 cases are idiopathic where there is generalized dysfunction of colonic smooth muscle at the cellular level. Colonic smooth muscle becomes less responsive to neurotransmitters and lacks normal activation of smooth muscle myofilaments (Washabau & Hasler, 1997). Causes of constipation and obstipation are listed in Table 1. 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%) (Washabua & Hasler, 1997). 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. 

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 (Figures 1&2) 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. 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

1) Mild constipation

Owners may present these cats for a variety of reasons. They may complain of firmer faeces in the litter tray, the cat taking excessive time to defaecate or unproductive efforts to defaecate. These cats may also have intermittent vomiting or reduced appetite as part of their history. 

In mildly affected, well cats, rectal suppositories and laxatives (dietary fibre and lactulose) may be all that is required in the short term – particularly if there has been an inciting cause that has been removed, such as the cat returning home from a boarding situation, clipping of matted hair around the anus (pseudocoprostasis) and treatment of a painful perianal conditions. Rectal suppositories can take many forms. Emollients such as dioctyl sodium sulfosuccinate (Coloxyl suppositories), or others such as glycerin (lubricant) and bisacodyl (Bisalax / Durolax) are often effective. Microlax enemas are a popular choice and contain emollients including glycerin. They are safe and convenient to use in cats. Occasionally owners are willing to use these on an “as needed” basis at home. Enemas are often combined with oral laxatives such as Microlax, at least in the short term (1-2 days) for improved efficacy. 

Owners can determine success of therapy if the cat uses a litter tray however hospitalisation of outdoor cats may be required so defecation can be observed. An outdoor cat may not be compliant to this if it is not used to using litter trays so sometimes a compromise has to be reached – for example, sending the cat home for re-assessment at the veterinary clinic the following day.

Lateral radiograph of a cat with megacolon	Megacolon prior to colectomy

2) Unwell cats

In un-well cats treatment often includes correcting any metabolic complications combined with manual evacuation of the colonic contents under deep sedation or anaesthesia. Because a significant proportion of these cases are older felines with possible intercurrent conditions, it is important to thoroughly evaluate each patient to assess whether hospitalisation and supportive treatment are necessary. In ill cats, a complete blood count, biochemistry and urine specific gravity and dipstick are important to determine what other underlying conditions may be present and may be contributing to or may be affected by other treatments.

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 (2-3mls/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. 

Once safely anaesthetised, and a cuffed endotracheal tube is placed, use a lubricated oesophageal feeding tube (8-10F) and instil a warm water and lubricant mix (mineral oil such as paraffin, lactulose or a lubricant jelly) via the rectum into the colon. Avoid excessive quantities of enema liquid (no more than 10mls/kg per enema), as this can lead to vomiting during anaesthesia or recovery, and subsequent aspiration pneumonia and/or oesophagitis. A combination of massaging the colon to move colonic contents towards the rectum (‘milking’) and digital removal of faeces with a gloved lubricated finger is often successful. In severely affected cats gentle manipulation with round tipped (sponge) forceps may help break up the faecal matter but care should be taken not to damage the colonic mucosa or cause perforation of the colonic wall. Phosphate enemas should be avoided in cats because of the likelihood of hyperphosphataemia, particularly in patients with renal compromise. 

Once stabilised and the faecal matter removed, cats are then suitable for chronic therapy. This may need to be considered multimodal where environmental, dietary and medical therapies need to be combined to achieve the most successful outcome. When these fail, or in cats that are unwilling to accept dietary changes or are impossible to medicate, colectomy should be considered.  

3) Chronic therapy

As cats can be private creatures, environmental factors that lead to them feeling insecure about defecating need to be considered as a potential cause for faecal retention and potential worsening of constipation. Providing a safe, convenient location of litter trays is essential, just as it is to prevent lower urinary tract problems. Simple things such as providing more litter trays, hooded litter trays or using a different type of litter may improve the cat’s defecating patterns. Hair ingestion may also contribute to constipation so attempts should be made to reduce this; grooming of longhaired cats and adequate flea control are such examples. Pseudocoprostasis, or constipation from matted hair around the anus can be a significant problem in longhaired cats. Medications that may be contributing to dehydration or colonic stasis (diuretics and opioids in particular) need to be reviewed and adjusted if possible.  

Laxatives

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.

Lactulose is an effective and well-tolerated laxative that also stimulates colonic fluid secretion and propulsion through the release of organic acids from its fermentation. It is generally given to effect, most cats requiring around 0.25-0.5ml/kg every 8-12 hours. Excessive quantities lead to liquid diarrhoea and the owner can simply reduce the dose. Lactulose often needs to be given directly via syringe, as few cats will tolerate it mixed with food. Emollient laxatives increase the miscibility of water and lipid in digesta (docusate sodium – Coloxyl) and are cheap and effective for mild to moderate cases of constipation . For cats with megacolon they are rarely enough to induce a normal defaecation pattern. They should not be administered with mineral oils such as paraffin oil, as they increase systemic absorption of these compounds.

Lubricant laxatives such as mineral oil and white petrolatum impede water absorption and lubricate firm dry faeces. I generally avoid liquids as they are tasteless and can be easily aspirated by the cat leading to lipid pneumonia which can be life threatening. Palatable pastes are often better tolerated and more convenient and there are a number marketed for veterinary use. Long-term side effects may include reduced absorption of vitamins, but in practice this is unlikely to be a significant problem. Lubricants are mainly useful only in mild cases and in those cats with hair ingestion contributing to constipation. Stimulant laxatives such as bisacody – Bisalax (5mg per cat per day) should be used sparingly as they may lead to damage of myenteric neurones and further worsen constipation and are only mildly effective.  

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 (Washabau and Hasler, 1997). 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. HCM). Many compounding pharmacies in Australia (e.g. Compoundia) are able to source and supply cisapride in a convenient capsule form.

Ranitidine (3.5mg/kg POq12h) and nizatidine (5mg/kg PO q24h) have been shown to stimulate colonic motility in vitro and may be useful in cats that fail to respond to cisapride or where cisapride is not available. Their effect in vivo may not be as successful.

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 (Figure 3). 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 (White, 2002). 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 (White, 2002). To enhance success and minimise complications, colonic surgery should only be performed by the experienced or preferably, specialist surgeon.

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.

Table 1  

Causes of constipation and obstipation

Table 2  

Drugs used in the treatment of constipation in cats

(Adapted from Burrows 1996)  

Burrows CF 1996 Constipation, obstipation and megacolon in the cat Waltham Focus, 6, 9-14

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.

Washabau RJ 2004 Feline constipation, obstipation and megacolon. Proceedings of the Western Veterinary Conference, 2004 (Vet-190)

White RN 2002 Surgical management of constipation Journal of Feline Medicine and Surgery, 4, 129-138