Constipation And How Best To Manage It In Cats
Constipation or difficulty passing faeces is a severely debilitating disease seen commonly in cats of all ages and is life-threatening if left untreated. Effective management requires recognition of the aetiology and choosing the appropriate therapy for both cat and owner.
Clinical examination reveals colonic impaction with varying degrees of dehydration, weight loss, debilitation and abdominal pain. Pelvic fracture malunion may be detected on rectal examination in cats with previous pelvic trauma. Rectal examination is also useful in identifying other unusual causes of constipation, such as foreign bodies, rectal diverticula, strictures, inflammation, or neoplasia. Chronic tenesmus may be associated with perineal herniation in some cases. A complete neurologic examination with special emphasis on caudal spinal cord function should be performed to identify neurologic causes of constipation, e.g., spinal cord injury, pelvic nerve trauma, and Manx sacral spinal cord deformity.
While it is important to consider an extensive list of differential diagnoses in an individual animal, it should be kept in mind that most cases are idiopathic, orthopedic, or neurologic in origin. A recent review suggests that 96% of cases of obstipation are accounted for by idiopathic megacolon (62%), pelvic canal stenosis (23%), nerve injury (6%), or Manx sacral spinal cord deformity (5%).
Table 1. Common Differentials for Feline Constipation
| Idiopathic megacolon |
| Mechanical obstruction |
| - pelvic deformity |
| - neoplasia causing intraluminal or extraluminal compression |
| - strictures |
| Metabolic |
| - hypokalaemia |
| - hypercalcaemia |
| - dehydration |
| - hypothyroidism |
| - renal disease |
| Neurologic |
| - spinal cord deformities (Manx) |
| - lumbosacral disease |
| - cauda equina |
| - ileus |
| Pain |
| - musculoskeletal |
| - anorectal |
| Dietary change |
The pathogenesis of idiopathic megacolon has been variably attributed to a primary neurogenic or degenerative neuromuscular disorder. Recent studies suggest that cats affected with idiopathic megacolon have impaired colonic smooth muscle function without significant abnormalities of smooth muscle cells or of myenteric neurons on histologic evaluation. These studies suggest that the disorder of feline idiopathic megacolon is a generalised dysfunction of colonic smooth muscle, and that treatments aimed at stimulating colonic smooth muscle contraction might improve colonic motility.
A complete blood count, serum chemistry, urinalysis and T4 level should be performed in all cats presented for constipation so that metabolic causes of constipation, such as dehydration, hypokalemia, and hypercalcemia may be detected. Serum T4 concentration and other thyroid function tests should also be considered in cats with recurrent constipation and other signs consistent with hypothyroidism.
Abdominal radiography should be performed in all constipated cats to characterise the severity of colonic impaction, and to identify predisposing factors such as intraluminal radio-opaque foreign material (e.g., bone chips), intraluminal or extraluminal mass lesions, pelvic fractures, and spinal cord abnormalities. The radiographic findings of colonic impaction cannot be used to distinguish between constipation, obstipation and megacolon in idiopathic cases.
Further diagnostic tests may be indicated in some cases. Extraluminal mass lesions should be further evaluated by abdominal ultrasonography and guided biopsy, whereas intraluminal mass lesions are best evaluated by colonoscopy. Colonoscopy requires general anesthesia and evacuation of impacted feces. It is used to evaluate the colon and anorectum for suspected inflammatory lesions, strictures, sacculations, and diverticula and. CSF analysis and myelography are indicated for neurogenic causes of constipation.
Successful management of constipation involves safely removing initial impacted faeces and then selecting therapies aimed at allowing effective defaecation on its own. Therapies are classified as either medical or surgical and are selected based on things such as the aetiology, severity, patient compliance and owner compliance.
Medical Therapy
Mild to moderate or recurrent episodes of constipation require medical intervention. Most cats can be managed as outpatients with dietary modification, water enemas, oral or suppository laxatives, and/or colonic prokinetic agents.
Mild constipation can usually be managed using rectal suppositories alone or combined with an oral laxative. A compliant cat and willing owner are required for success. Several types of suppositories are available and include dioctyl sodium sulfosuccinate (emollient laxative), glycerin (lubricant laxative), and bisacodyl (stimulant laxative).
Mild to moderate or recurrent episodes of constipation may require administration of enemas and/or manual extraction of impacted faeces. Several types of enema solutions may be administered, such as warm tap water (5-10 mL/kg), warm isotonic saline (5-10 mL/kg), dioctyl sodium sulfosuccinate (5-10 mL/cat), or lactulose (5-10 mL/cat). Enema solutions should be administered slowly with a well-lubricated 10-12F rubber catheter or feeding tube.
Cases unresponsive to enemas may require manual extraction of impacted faeces. Cats should be adequately rehydrated and then anesthetised and intubated to prevent aspiration should colonic manipulation induce vomiting (many cats vomit watery faeces on recovery from a water pic enema). Warm water is infused into the colon through a water pic enema while the faecal mass is manually broken up by abdominal palpation. Whelping forceps may also be introduced rectally (with caution) to break down the faecal mass. A water pic enema safely and rapidly removes faeces reducing the risks of prolonged anesthesia and colonic perforation. This method has never failed in our clinic and as such I believe surgical removal of faeces via colotomy has no place in feline medicine. Laxative and/or prokinetic therapy may then be instituted once the faecal mass has been removed.
Many constipated cats will respond to bulk-forming laxatives. These are dietary fiber supplements of poorly digestible polysaccharides and celluloses derived principally from cereal grains, wheat bran, and psyllium. Dietary fiber is preferred as it is well tolerated, more effective, and more physiologic than other laxatives. Fiber supplemented diets are available commercially (eg Hills R/D and W/D) or owners may add psyllium (1-4 tsp per meal), wheat bran (1-2 tblsp per meal), or pumpkin (1-4 tblsp per meal) to their normal canned cat food. Cats should be well hydrated before commencing fiber supplementation to maximise the therapeutic effect and to minimise the impaction of fiber in the constipated colon.
A final group of laxative is the poorly absorbed polysaccharides. Lactulose is the most effective agent in this group and probably the only one worth mentioning. The organic acids produced from lactulose fermentation stimulate colonic fluid secretion and propulsive motility. Lactulose administered at a dosage of 0.5 mL/kg every 12hrs fairly consistently produces soft feces in cats. Most cats with recurrent or chronic constipation can be well managed with lactulose. The dosage may have to be tapered in individual cases if flatulence and diarrhea become excessive.
The stimulant laxatives are a diverse group of agents that have been classified according to their ability to stimulate propulsive motility. Bisacodyl, at a dosage of 5 mg q 24 h PO, is the most effective stimulant laxative in the cat. It may be given individually or in combination with fiber supplementation for long-term management of constipation. It is suggested that daily administration of bisacodyl be avoided because injury to myenteric neurons can occur with chronic usage. We do not routinely use stimulant laxatives in our clinic.
Prokinetic Drugs
1. Cisapride enhances colonic propulsive motility through activation of colonic smooth muscle 5-HT receptors in a number of animal species. In vitro studies have shown that cisapride stimulates feline colonic smooth muscle contraction. The commercial formulation of cisapride (Prepulsid) was withdrawn from human markets several years ago, but the drug is readily available through compounding pharmacies. Laboratory studies have shown that classic histamine H-2 receptor antagonists ranitidine and nizatidine, stimulate feline colonic smooth muscle contraction in vitro but it is not yet clear how effective these drugs are in vivo. While cisapride was unavailable, we used ranitidine 15mg bid with apparent success.
2. Tegaserod (Zelnorm®-Novartis Corporation) is a potent partial non-benzamide agonist at 5-HT4 receptors and a weak agonist at 5-HT1D receptors. Tegaserod has prokinetic effects in the canine colon although the motor mechanisms responsible are unclear. Its safety and efficacy in cats is unknown and the author has no personal experience using this drug in cats so caution should be exercised.
In vitro studies suggest that tegaserod does not delay cardiac repolarization or prolong the QT interval of the electrocardiogram as had been occasionally reported with cisapride.
Clinical efficacy has been demonstrated in human constipation-predominant irritable bowel syndrome (IBS) and the drug was approved for the treatment of this disorder in the U.S. in 2002.Gastric and intestinal effects of tegaserod have not been reported in the dog, so this drug may not prove as useful as cisapride in stimulating proximal gastrointestinal motility.
3. Prucalopride (Janssen Pharmaceutical) is a potent partial benzamide agonist at 5-HT4 receptors, but is without effect on other 5-HT receptors or cholinesterase enzyme activity. Unlike tegaserod, prucalopride also appears to stimulate gastric emptying in dogs.
In lidamidine-induced delayed gastric emptying in dogs, prucalopride (0.01-0.16 mg/kg) dose-dependently accelerates gastric emptying of dextrose solutions.
Prucalopride dose-dependently (0.02-1.25 mg/kg) stimulates giant migrating contractions (GMC's) and defecation in the dog. The prucalopride effect is observed most prominently in the first hour after administration, suggesting that the prucalopride effect is a direct effect on the colon rather than on total gut transit time. Prucalopride also enhances defecation frequency in healthy cats. Cats treated with prucalopride at a dose of 0.64 mg/kg experience increased defecation within the first hour of administration. Fecal consistency is not altered by prucalopride at this dosage. Prucalopride has not yet been approved in the U.S.
4. Misoprostol is a prostaglandin E1 analogue that reduces the incidence of nonsteroidal anti-inflammatory drug-induced gastric injury. The main side effects of misoprostol therapy are abdominal discomfort, cramping, and diarrhea. Dog studies suggest that prostaglandins may initiate a giant migrating complex pattern and increase colonic propulsive activity. Given its limited toxicity, misoprostol may be useful in dogs and cats with severe refractory constipation. Misoprostol was recently shown to stimulate feline colonic smooth muscle contraction in vitro.
Surgical Therapy
Most surgical therapies for constipation in the cat are related to the management of idiopathic megacolon, although causes such as pelvic outlet obstruction, complications of neutering surgery, perineal herniation, and malunion pelvic fractures may also require surgical intervention. Cats with megacolon which are refractory to medical therapy or unable to be medicated, should have their colon surgically removed via a total or sub-total colectomy. A sub-total colectomy involves removal of the majority of the colon except for the ileocolic valve and the proximal colon followed by anastomosing the proximal colon to the distal colon or rectum. A total colectomy involves removal of the entire colon, the ileocolic valve, cecum and distal ileum followed by ileorectal anastomosis.
Sub-total colectomy is an easier and faster surgery to perform than a total colectomy and stools return to normal faster after surgery with sub-total (1-2 weeks) compared with a total (4-10 weeks). A study of 25 cats treated with either total or sub-total colectomy failed to show a difference in long-term recurrence rates so currently, the recommended best surgical therapy for megacolon is sub-total colectomy with the ileocolic junction preserved. In my experience, recurrent constipation is more likely to recur with this technique. Hence I perform a total colectomy in young cats, Burmese cats and cats with idiopathic dilated megacolon to ensure optimal long-term results.
Surgical correction of pelvic canal stenosis may be performed by pelvic osteotomy or pubic symphyseal distraction and may be sufficient alone for some cats suffering from pelvic canal stenosis. Pelvic osteotomy without colectomy has been recommended for cats with pelvic fracture malunion and megacolon of less than 6 months duration. A colectomy can be performed if osteotomy is not curative. Pelvic osteotomies are technically very difficult making some surgeons prefer colectomy.
We often perform a somewhat elective colectomy very early with little or no medical management. Using a 3 year old Burmese cat with faecal impaction from megacolon as an example, if treated medically would need iv fluids, an anaesthetic, water pic enema and hospitalisation which on average may cost $500. Then it is discharged with increased dietary fibre and medicated twice daily with 5mg cisapride bid ($1.30/capsule) and 2mls duphalac. The cost of cisapride alone is $950/year. So if there are no relapses and no revisit consultations, in the first year a constipated cat may cost $1500 and need to be orally medicated twice daily and be forced to eat a high fibre. If the same 3 year old Burmese cat with faecal impaction and megacolon was taken straight to colectomy, it would have iv fluids, an anaesthetic, colectomy, 2-3 nights in hospital and be discharged on antibiotics for 7 days and likely never need medicating again. The cost for a colectomy at our clinic is about $1500. Thus there are very clear reasons why colectomy is often the best initial therapy.
Procedure for sub-total colectomy
- pre-anaesthetic iv fluids at 2 x maintenance
- pre-medicate with methadone and midazolam, induce with alfaxan, intubate and maintain on isoflourane/oxygen
- start intravenous fentanyl CRI which continues for 6-8hrs post-surgery
- prophylactic antibiotics of either cephazalothin or amoxicillin/gentamycin iv
- place transdermal fentanyl patch behind neck (Durogesic 25ug)
- doppler blood pressure measured every 5-10 minutes
- routine caudal laparotomy, colon exteriorised, caudal mesenteric vessels ligated with vascular staples or 2-0 silk, proximal and distal colon manipulated into anastomosis position and arcuate vessels appropriately ligated with 4-0 pds, doyen bowel clamps placed just cranial and caudal to where arcuate vessels were ligated, bowel resected with metzenbaums and disposed of
- end-to-end anastomosis of proximal to distal colon using 4-0 pds and a simple continuous suture pattern
- clamps are released and anastomosis tested for leakage
- abdomen flushed with warm sterile saline 3 times and closed routinely with 3-0 pds
- repeat prophylactic antibiotics on recovery and again in 6 hrs, change to clavulox the following morning
- cats are offered food and encouraged to eat as soon as recovered from anaesthesia (approx 60 mins)
- cats remain in hospital until eating, normothermic and no significant fluid loss in faeces. This is typically 2-3 days.
- fentanyl patch removed and discharged on clavulox orally for 7 days and sutures out 10 days post surgery
Cats have a very favorable prognosis for recovery following colectomy, although mild to moderate diarrhea may persist for weeks to months postoperatively in some cases. In the majority of cases, the long-term outcome following subtotal colectomy is considered excellent.
Perineal Hernia
Perineal hernia is a rare disease in cats and is characterised by tenesmus and constipation. It occurs due to a weakness of the muscles and fascia of the pelvic diaphragm allowing deviation or dilation of the rectum into the perineum or less commonly, caudal displacement of abdominal organs. Unlike dogs, abdominal contents are rarely herniated. Instead there is lateral bulging of the rectum containing faecal balls and this bulging is also termed anal sacculation or pre-anal faecolith. This can cause marked and continual discomfort requiring manual extraction and is a common reason for presentation.
A presumptive diagnosis is often made based purely on the owner’s history. The bulk of the faeces is usually in the litter tray but small faecal balls are also found dropped all around the house. Owners may wrongly interpret this as intentional inappropriate toileting. When defaecating, cats with perineal hernias can either have trouble getting started (as the first piece of faeces fails to exit through the anal sphincter and doubles back on itself) or finished (the last piece of faeces fails to exit and forms a pre-anal faecolith). These cause significant pain and cats often run around the house screaming and biting at their back end until it either pops out or is extracted by a veterinarian (usually under sedation or GA). A definitive diagnosis is made by demonstrating marked lateral rectal deviation in the area between anal sphincter and ischium. A diagnosis of perineal hernia can be easily made by digital rectal examination but is often overlooked due to a lack of recognition of the disease entity.
We have found siamese cats to be over represented and male cats more commonly affected. This breed association has not previously been recognised in the literature. Primary or idiopathic perineal herina occurrs in younger cats (mean=2.8yrs, range=1.5-4yrs) while perineal hernia associated with megacolon occurrs in older cats (mean=11.9yrs, range=8.5-15.3yrs). Perineal hernia can be associated with previous tail amputation or perineal urethrostomy although we have never seen a case of the latter. We have seen perineal hernia with caudal displacement of the urinary bladder in two Burmese cats also suffering cutaneous asthenia.
Medical management of perineal hernia is similar to that used for constipation (see below) and unfortunately is usually unsuccessful. Surgical management is regarded as the treatment of choice and may involve colectomy, internal obturator transposition herniorrhaphy, or both. Primary or idiopathic perineal hernia is best corrected using an internal obturator transposition herniorrhaphy. A colectomy should be performed first in cats with perineal hernia associated with megacolon as this may resolve clinical signs for many years. If a herniorrhapy is performed first in these cases, they are unable to pass faeces at all and require a colectomy for relieve. Careful assessment of cats with perineal hernias associated with megacolon is essential so the correct surgical procedure be performed. It has been a steep learning curve and even when armed with this knowledge, the author admits to performing many surgeries in the wrong order.
