Treating constipation in cats

Introduction

“Constipation” is a commonly encountered problem in feline practice that can lead to significant morbidity, and can even be the reason some owners will opt for euthanasia of their pet, and it is firstly important to use the correct relevant definitions (Box 1) to aid accurate discussion and case management. There are many causes of constipation in cats, with idiopathic megacolon being the most common 1, and clinicians therefore need to be able to identify the etiology in order to initiate a patient-tailored management plan.

Box 1. Definitions 1.

Note: these distinctions have important implications for patient management and prognostication.

Etiopathogenesis

The causes of constipation can be classified mechanistically (see Box 2), although note that in any individual cat several of the listed mechanisms may simultaneously contribute to the problem. For example, a cat with constipation due to idiopathic megacolon may stop eating and drinking, consequently becoming dehydrated and hypokalemic, worsening the constipation. Although there are many potential causes, a review of published cases noted that 62% of cats with obstipation had idiopathic megacolon, 23% had pelvic canal stenosis, 6% had nerve injury, and 5% had Manx sacral spinal cord deformity 1. In a recent retrospective study, older cats, overweight cats, cats with chronic kidney disease, and those with a previous history of constipation were more likely to present to an emergency room for constipation 2.

By definition, the etiopathogenesis of idiopathic megacolon in cats is not fully understood. Ex vivo experiments using colonic tissue harvested from constipated cats has demonstrated generalized dysfunction of colonic smooth muscle, although it is not known if this was the initiating cause of constipation or a secondary effect 3. Additionally, histopathological assessment of the affected tissue did not reveal any abnormalities of the smooth muscle (longitudinal or circular) or myenteric plexus.

Box 2. Causes of constipation in cats 1.

Clinical features

The signalment of constipated cats is very variable, as animals of either sex and any age or breed can develop this problem. In a review of published cases, the mean age was reported to be 5.8 years, with 70% of cats being male (although this gender bias has not been noted in the author’s own experience), and commonly reported breeds included domestic shorthair (46%), domestic longhair (15%) and Siamese (12%) 1.

Affected cats are often observed to make multiple unsuccessful attempts to defecate (Figure 1), and may vocalize while doing so. Sometimes they can pass small amounts of very firm feces, or they produce small amounts of liquid stool, or will have hematochezia 1. The latter two scenarios can lead to an owner believing that their cat’s main problem is diarrhea. Constipation should also be differentiated from lower urinary tract disease, colitis, and anal sac disease, all of which can lead to apparent tenesmus and increased use of litter boxes. Conversely, any of the above signs of constipation can be easily missed in multi-cat households, so it is therefore important to be very careful when defining the patient’s problems. With chronicity, vomiting, anorexia, or lethargy may occur, and if constipation is part of a multisystemic disease process (e.g., dysautonomia) other systemic signs may be present. The owner also should be asked carefully about any medications/therapies that the cat has received, as some can lead to colonic hypomotility, dehydration, or iatrogenic hypothyroidism (Box 2), as well as any recent environmental or behavioral changes.

It is usually possible to transabdominally palpate impacted feces within the colon of constipated cats, but this can be challenging in severely obese or fractious patients. Affected cats may also show signs of nausea or dehydration. A neurological examination, including spinal palpation, and an ophthalmic examination should be performed to determine if constipation is part of a more widespread neuromuscular disorder (e.g., dysautonomia, spinal cord disease). A careful rectal examination performed under sedation or anesthesia may reveal the presence of impacted feces, rectal masses, foreign bodies, displaced pelvic fractures, rectal strictures or anal sac disease. Occasionally cats may develop perineal herniation as a result of prolonged fecal tenesmus.

Diagnostic testing

It is recommended to perform a complete blood count, chemistry panel and urinalysis in cats with recurrent or severe constipation. These usually do not lead to identification of an underlying cause, but can occasionally do so (e.g., hypokalemia, hypercalcemia, dehydration, renal azotemia, or changes suggestive of hypothyroidism). If the cat’s FeLV/FIV status is not already known, it should be determined.

Abdominal radiography should be performed for all constipated cats. This imaging modality allows the detection of impacted feces and assessment of the severity of impaction (Figure 2). Luminal (e.g., radiopaque foreign material) and extraluminal colonic obstruction (e.g., pelvic canal stenosis due to a displaced fracture (Figure 3)) may also be appreciated. Obvious spinal cord lesions (e.g., fractures or tumors) may also be apparent. Research has shown that the ratio of the maximal diameter of the colon to the length of the L5 vertebral body can help differentiate constipation from megacolon; a ratio < 1.28 indicates a normal colon, while a value of > 1.48 indicates megacolon (sensitivity 77%, specificity 85%) 4. Repeating abdominal radiographs after treatment also allows the clinician to assess the patient’s response.

Further evaluation may be done as necessary. The clinician’s first diagnostic aim should be to confirm the presence of constipation and to determine its chronicity and severity, and this can usually be achieved through a physical examination and radiography as described above. Given that idiopathic megacolon and pelvic canal stenosis account for about 85% of cases 1, an extensive diagnostic workup is not necessary for most constipated cats, but it is important not to miss a treatable underlying cause in an individual patient. Potential indications for further diagnostic testing include neurological deficits (e.g., those associated with dysautonomia), palpable abdominal or recto-anal masses, radiographically detected abdominal/pelvic canal abnormalities, disproportionate dwarfism in young cats (consistent with congenital hypothyroidism), or other signs of systemic illness. Examples of additional tests that are sometimes needed include thyroid testing (i.e., total T₄, free T₄, thyroid-stimulating hormone measurement) if hypothyroidism is a possibility, abdominal ultrasound if mural or extraluminal colonic masses are suspected, cross-sectional imaging if vertebral disease or intrapelvic masses are a concern, or colonoscopy to look for inflammatory lesions, recto-anal strictures or diverticula.

Outpatient management

Nutrition

Initially, some mildly affected cats can be managed on an outpatient basis with dietary changes alone. Fiber supplementation is a commonly employed nutritional strategy in constipated cats, and there are various types of dietary fiber and fiber sources, each with different potential benefits. Fiber supplementation has shown to be beneficial in adult humans with chronic constipation 5, but supplementation with some types of fiber has the potential to worsen constipation. Fibers that are fermented by colonic bacteria lead to increased production of short-chain fatty acids, including butyrate which acts as an energy supply for colonocytes. Short-chain fatty acids also have anti-inflammatory properties and have been shown to stimulate longitudinal but not circular contractions of the canine and feline colon 6,7. Non-soluble, non-fermentable fibers are bulk forming and potentially improve colonic motility by distending its wall, thereby stimulating contraction. These fibers have the potential disadvantage of reducing nutrient absorption and fecal water content, and the latter effect could potentially lead to worsened fecal impaction, especially in an already dehydrated and obstipated patients, or in those that have a megacolon. Psyllium, a soluble but (mostly) non-fermentable fiber, leads to the formation of a gel (Figure 4 and 5) that provides lubrication and increases the frequency of defecation in humans with idiopathic constipation (with doses of 10 g/day and a duration > 4 weeks apparently optimal in human patients) 5.

In two field trials, a commercially available highly digestible moderately psyllium-supplemented dry extruded diet was shown to be palatable and allow the withdrawal of other medications in constipated cats 8. Note that neither trial was controlled, and so it was not confirmed that the improvement observed was due to the diet alone, therefore future randomized controlled clinical trials are needed. However, anecdotal experience with this diet is also positive, and it is the author’s choice for managing constipation in most cats. Another option is to add unflavored psyllium husk (approximately 1-2 teaspoons/5-10 mL per meal) or other fiber sources to the cat’s existing diet, but this can affect palatability.

An alternative nutritional strategy is to feed a highly digestible, low residue intestinal diet to reduce the volume of material reaching the colon. This strategy has been suggested to be particularly beneficial in cats with severe disease that cannot tolerate extra fecal volume. Gastrointestinal diets are also often supplemented with fermentable fiber.

Maintaining adequate hydration is crucial for successful treatment. Water (filtered/bottled if necessary) should be freely available in different shaped bowls or via a fountain to help ensure this, and feeding a canned (rather than dry) diet can also help.

Laxatives

In more severely affected cats, or those with recurrent bouts of constipation, it is often necessary to start medical therapy. There are a wide variety of different classes of laxatives available (i.e., osmotic agents, bulk forming substances, emollients [stool softeners], or motility-stimulating [prokinetic] drugs). However, the author limits his use of laxatives in cats to the two osmotic agents discussed below.

The osmotic laxative agent polyethylene glycol (PEG)3350 is hydrophilic, binding water molecules to reduce the movement of water out of the colon, and consequently both softening and bulking its contents 9. Various forms of this agent without electrolytes are available over the counter in some countries for the treatment of constipation in humans. Metanalysis of clinical trials in adult and pediatric human patients suggest that PEG3350 is more effective and better tolerated than lactulose 10,11,12 and this agent is the author’s preference for treating cats with constipation because of its palatability and efficacy. A pilot study of PEG3350 in 6 healthy cats has demonstrated good palatability and stool softening, and no adverse effects were noted, although small non-clinically significant increases in serum potassium occurred in some cats 13. Therefore, rechecking serum electrolytes after initiation of therapy is recommended.

Lactulose is a non-absorbable disaccharide that is osmotically active, although it is fermented by colonic bacteria and can lead to bloating or flatulence in humans. This agent appears to be less palatable to cats than PEG3350 but it can also be effective.

The author recommends both products should be started at a low dose and then titrated to effect; PEG3350 can be given at an initial dose of 0.6-1.25 mL (1/8-1/4 tsp) of powder per cat q12H (mixed with food), whilst lactulose can be dosed at 0.5 mL (1/10 tsp)/kg q8-12H PO. It takes several days for either agent to have its full effect, and so dose escalation should be performed slowly. Overdosage of either agent can lead to diarrhea, dehydration, or electrolyte abnormalities.

Prokinetic drugs

In some cats prokinetic agents are also required; these are given as maintenance treatment once impacted fecal matter is no longer present in the colon. When available, the author’s agent of choice is the serotonin (5-HT₄) receptor agonist cisapride at 0.5 mg/kg PO q12H. This drug has been shown to stimulate motility in ex-vivo colonic tissue from cats with idiopathic megacolon 14, and anecdotally seems to be effective and well tolerated by constipated cats. It was withdrawn from the human market following reports of fatal cardiac arrhythmia (torsades de pointes) due to the drug’s effects on other 5-HT receptor types present in the myocardium. This adverse effect has not been reported in feline patients, although one study did observe prolonged Q-T intervals in cats given 60 times the therapeutic dose for 7 days 15. Cisapride may be still sourced from accredited veterinary compounding pharmacies in many countries.

Tegaserod is another 5-HT₄) receptor agonist that has been shown to speed transit in the canine colon when given intravenously 16, although its effect in cats has not been described in the literature. Again, it was withdrawn from the US market because of cardiac safety concerns in humans, but was recently reintroduced under more selective labeling 17. Prucalopride is another, more specific, 5-HT₄ receptor agonist that has been shown to induce defecation in cats 18, but its use is off-label. The author has no personal experience using tegaserod or prucalopride and so cannot advocate their use. The histamine-2 receptor agonist ranitidine also has an anticholinesterase effect, and in one study (reported in the form of an abstract) has been shown to induce motility in feline colonic tissue ex vivo 19. However, efficacy has not yet been demonstrated in vivo.

Other strategies

Wherever possible, it is essential to address the underlying medical cause of constipation (e.g., with thyroxine supplementation in hypothyroid cats). Interestingly, in a study of cats with pelvic fractures, of which 74% were surgically managed, constipation was an uncommon complication, occurring in only 8% of cases, and megacolon did not develop in any cats 19. Thus, surgery stabilization could be considered in a cat with a pelvic fracture that results in pelvic narrowing to avoid later development of megacolon.

Results of a pilot study suggested that a commercially available probiotic mixture may lead to improved signs and reduced colonic inflammation in cats with constipation 20, but further research is needed and it is not expected that all probiotics would have the same effect.

A variety of feline/pediatric enema products and suppositories of appropriate volumes for use in cats are available (e.g., those containing dioctyl sodium sulfosuccinate and glycerin, or docusate sodium, PEG, and glycerin). However, the author does not typically advocate their use at home by clients due to the burden this places on the animal-human bond.

Finally, if environmental or behavioral factors are believed to have played a role in the development of constipation, these may also need to be addressed.

Inpatient management

More severely affected constipated cats require hospitalization. Dehydration is a contributing factor or a complication in many cases, and must be addressed for a successful outcome. Intravenous fluids (often initially balanced replacement crystalloid solutions) can be administered to restore/maintain adequate hydration and help correct any electrolyte abnormalities.

Warm water, physiological saline, or lactated Ringer’s solution enemas (5-10 mL/kg) are usually well tolerated and are often helpful. If desired, a water-soluble lubricant can be added to these. A lubricated red rubber catheter is usually used to deliver the enema and must be advanced gently several centimeters into the colon, but this can be difficult with severe fecal impaction. Administration may need to be repeated several times with an appropriate interval (often 6-24H). Enema administration can lead to vomiting and subsequent aspiration of intestinal contents in cats, but the risk can be minimized by administering it under general anesthesia with an endotracheal tube in place. However general anesthesia is not always possible or in the cat’s best interests, in which case several small-volume enemas rather than a single high-volume enema should be administered. Pretreatment with the antiemetic maropitant (1 mg/kg IV) is advised before enema administration, and PEG3350 or lactulose can be given by mouth concurrently to cats that can tolerate oral medications. Note that phosphate-containing enemas are contraindicated in cats, as they can lead to potentially fatal hypernatremia, hyperphosphatemia or hypocalcemia.

Manual extraction of even severely impacted feces can be avoided in most cats by administering a PEG3350 solution (usually products which are used for pre-endoscopic colonic preparation in human patients) at a constant slow rate via an indwelling nasoesophageal tube. A study of 9 cats described using an administration rate of 6-10 mL/kg/H, with a median total dose of 80 mL/kg (range: 40-156 mL/kg) and reported a median time to significant defecation of 8 hours (range 5-24H) 21. Care must be taken to ensure proper placement of the nasoesophageal tube, including lateral radiographs of the cervical region and thorax, and the cat should be monitored carefully to avoid aspiration. It is also good practice to periodically check the cat’s hydration status and serum electrolyte concentrations during hospitalization.

Occasionally, digital extraction of feces is required, but this should only be performed under general anesthesia with an endotracheal tube in place. First, warm water, physiological saline, or lactated Ringer’s solution – again possibly mixed with a water-soluble lubricant – is given as an enema to rehydrate the feces. After allowing several minutes for rehydration to occur, manual extraction is attempted by gently using a finger to remove the feces while simultaneously moving more feces distally into the pelvic canal via caudal abdominal palpation. This cycle is repeated as necessary. The author does not use whelping forceps or other instruments during this process. Sometimes it is not possible to fully “deobstipate” a cat at the first attempt and the procedure needs to be repeated on a subsequent day; this is preferable to a single prolonged attempt. Possible complications include colonic trauma, colonic perforation, aspiration, and anesthetic-related problems. Some clinicians will administer pre-procedure antimicrobials (e.g., metronidazole) because of the risk of bacterial translocation.

Surgical management

In cats where an underlying cause is not identified or cannot be adequately addressed and that fail to respond to rigorous medical management, subtotal colectomy may be the only remaining option. Whilst careful medical management will allow this major surgery to be avoided in many cats, it is also important not to wait until refractory patients are severely debilitated before recommending it. The specific protocol is, however, outside the scope of this paper.

In a recent retrospective study of 151 cats undergoing subtotal colectomy, removal of the ileocolic junction was associated with less favorable outcomes than where it was preserved, and regardless cats often had diarrhea for several months after surgery. Encouragingly, the authors also found that subtotal colectomy was associated with long survival times and a high rate of owner satisfaction 22.

Conclusion

Constipation is a frequently encountered problem in small animal practice, and it is important to stress that it is not always easy to identify the underlying cause or to successfully treat the condition. Affected cats can develop significant morbidity over time, which can lead to an owner requesting euthanasia of their pet, so it is vital for the clinician to be proactive. Basic diagnostics will usually pinpoint if there is a primary cause, and the clinician can develop an appropriate management plan for each individual animal.