Constipation is the infrequent and difficult evacuation of feces with retention of feces within the colon and rectum. Obstipation is intractable constipation. The typical feline patient is middle-aged and male. Many cats have one or two episodes of constipation without any further problems. However, chronic constipation and obstipation may result in megacolon where a dilated large bowel is poorly responsive to therapy. Cats with idiopathic megacolon have generalized dysfunction of colonic smooth muscle. Some of the more common underlying causes of constipation include:
1. Drugs: especially opiates, anticholinergics, sucralfate
a. Stressors, e.g., changes in the home or routine
b. Litter box aversion
3. Difficulty defecating:
a. Pain in rectal or perineal area
b. Orthopedic problems, e.g., arthritis
c. Neurologic problems
4. Fecal factors:
a. Excessive fecal bulk
5. Colon factors:
a. Mass: intra- or extra-luminal
b. Obstruction due to narrowed pelvic canal, e.g., from previous trauma
a. Dehydration, e.g., due to chronic renal disease
b. Idiopathic megacolon
In one review, 62% of cases were due to idiopathic megacolon and 23% to pelvic canal narrowing. Whenever possible, the underlying cause should be identified and corrected.
The clinical signs of constipation are typically obvious to the owner, such as tenesmus, and scant hard dry feces, sometimes with blood. However, cats will also strain in the litter box due to lower urinary tract obstruction and owners may misinterpret this as due to constipation. Occasionally, constipated cats will have intermittent diarrhea as the colon is irritated due to hard dry fecal matter. Other clinical signs are non-specific, such as vomiting, inappetence and lethargy.
Physical examination confirms the presence of large amounts of feces in the colon sometimes accompanied by abdominal pain. The colon often palpates as a long firm tube or feces may be palpated as discrete concretions. A careful evaluation (e.g., musculoskeletal system, caudal spinal cord function, anorectal area) should be made for underlying causes. A rectal exam should be performed, under sedation if necessary, for masses, pelvic fracture malunion and anal gland abnormalities. A minimum database (CBC, serum chemistries/electrolytes, urinalysis) should be assessed, especially to determine hydration and electrolyte status and identify underlying diseases such as chronic renal disease. Survey abdominal radiographs are useful to confirm the diagnosis and assess severity as well as to evaluate for potential underlying causes, such as previous pelvic trauma and arthritis. The diameter of the colon on a lateral view should be approximately the same length as the body of the 2nd lumbar vertebra. Enlargement of the colon beyond 1.5 times the length of the body of the 7th lumbar vertebra has been proposed as indicating chronic dysfunction and megacolon. One study of 11 cats with megacolon found the mean diameter of the colon was 2.7 times greater than the length of the 7th lumbar vertebra (median: 2.4, range 1.8–3.3).
The first step in management is removal of obstructing feces with enemas and correction of dehydration with intravenous fluid therapy. One or two doses of a 5 mL microenema containing sodium lauryl sulfoacetate (MicroLax) is easily administered and will usually produce results within 20–30 minutes. Obstipated cats will require warm water or isotonic saline enemas (5–10 mL/kg). Safe additions to the water include mild soap, mineral oil (5–10 mL/cat), or docusate (5–10 mL/cat). Lactulose solution can also be administered as an enema (5–10 mL/cat). Sodium phosphate containing enemas must not be used as they can induce life-threatening hypernatremia, hyperphosphatemia and hypocalcemia in cats. Enemas are administered slowly with a lubricated 10–12 French feeding tube. In severe cases, manual manipulation of the feces via abdominal palpation or per rectum (manual disimpaction) under sedation or general anesthesia is also required. In these cases, opioids should be administered for pain relief.
An alternative to enemas is administration of an oral polyethylene glycol (PEG 3350) solution (e.g., CoLyte, GoLytely). A nasoesophageal tube is placed and the solution is given as a slow trickle (6–10 mL/kg/hour) over 4–18 hours. Defecation usually results in 6–12 hours. In a retrospective study of 9 cats, median time to defecation was 8 hours and the median total dose of PEG 3350 was 80 mL/kg. No adverse effects were noted.
In addition to management of any underlying conditions, long term medical treatment involves a combination of prokinetic agents, laxatives and dietary therapy. Cisapride stimulates contraction of feline colonic smooth muscle. A typical starting dose is 2.5 mg/cat BID, PO and it is better absorbed when given with food. Doses up to 7.5 mg/cat, TID have been reported. The drug is only available from compounding pharmacies in most countries. Hyperosmotic laxatives include lactulose and PEG 3350; they stimulate colonic fluid secretion and propulsive motility. The dose of lactulose solution is 0.5 mL/kg, PO, BID–TID. Lactulose is also available as crystal meant to be mixed in liquids for human use (Kristalose). A suggested dose is 3/4 tsp. BID with food. PEG 3350 is available as a powder meant to be mixed in liquids for human use (MiraLAX). A suggested dose for cats is 1/8 to 1/4 tsp. BID in food.
Dietary therapy has included the use of high fiber diets (> 20% on as fed basis) and low residue diets. Increased dietary fiber increases the production of short chain fatty acids which stimulate feline colonic smooth muscle contraction. Dietary fiber is also a bulk laxative and will increase fecal bulk, which will not be beneficial for all patients. Feeding a canned diet is often recommended to reduce fecal bulk and to ensure adequate water intake and hydration. Psyllium powder can be mixed with canned food at 1–4 tsp. SID–BID. A certain amount of trial and error is necessary to determine the best diet type for an individual patient.
Recently, a moderate fiber, psyllium-enriched dry extruded diet was introduced for management of gastrointestinal conditions in cats (Royal Canin Gastro Intestinal Fiber Response). In one report, 15 cats with recurrent constipation refractory to usual medical and dietary management were successfully treated with the Fiber Response diet. After 1 month on the diet, 14 cats had no clinical signs of constipation. The remaining cat was clinically normal after 2 months on the diet. Improvement was noted in 10/15 cats after only 7 days of dietary therapy.
Subtotal colectomy (95–98% excision, with preservation of the ileocolic junction) should be considered for cats that are refractory to medical and dietary therapy. Long term outcome is considered excellent. Most patients will experience transient diarrhea in the immediate post-operative period (1–6 weeks). In a small number of patients, diarrhea will persist.
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