Feline megacolon and colonic neoplasia (Proceedings)


Feline megacolon and colonic neoplasia (Proceedings)

Nov 01, 2010

Megacolon occurs more frequently in cats than dogs and is usually seen in middle-aged to geriatric cats. The ascending, transverse, and descending colon are chronically large in diameter and filled with dry stool. A congenital form of the disease has been seen especially in Manx cats with rectal/anal atresia and a sacral spinal deformity. An acquired form of the disease has been seen secondary to mechanical obstruction caused by malunion of pelvic fractures that have not had surgical treatment. Mechanical obstructions such as those caused by pelvic fractures may be relieved by removal of the cause of the obstruction if the abnormality is corrected within approximately 6 months; beyond that time frame irreversible changes apparently occur within the myoneural structure of the colon and obstruction persists even if the cause is treated effectively. Another unusual cause of acquired megacolon reported on several occasions is obstruction caused by uterine horn remnants following ovariohysterectomy in the female. Constipation has also been reported as a presenting sign in animals that are hypercalcemic with primary hyperparathyroidism.

Idiopathic megacolon is the most common form of the disease seen in cats. This disease is thought to be caused by an abnormality in the smooth muscle of the colon. Investigators at the University of Pennsylvania have shown that the colon of affected cats does NOT have normal motility as a result of a muscular rather than nervous abnormality. Some have suggested that anything causing pain or discomfort that may inhibit the animal from defecating may be a predisposing cause. Such causes could be spinal, pelvic, or rear limb related. Whatever the cause, as the dry stool continues to accumulate, colonic distension causes irreversible change in colonic smooth muscle and nerves and colonic inertia results. Medical management is variably (charitable word) effective in my experience. Surgical treatment with subtotal colectomy has been a very rewarding procedure for owners AND their cats for this disease over the past 15 years.

A. Clinical Signs
Usually develop over a period of time. Males are apparently more commonly affected than females.
      1. Constipation
      2. Tenesmus
      3. Obstipation
      4. Anorexia, weight loss
      5. 5. Dehydration, weakness, vomiting (Electrolytes!!)
      6. Combination of dry stool/diarrhea in some cases

Abdominal palpation, digital rectal examination, neurologic examination, and abdominal radiographs are performed to rule out concurrent disease such as neoplasia, strictures, or perineal hernias. Abdominal radiographs may help in identifying pelvic or spinal lesions. I recently performed colectomy in a 6 month old cat with apparent rectal stricture. IF you do find a perineal hernia on rectal exam which should be fixed first?? Probably depends on duration of signs, if relatively acute, I would fix the hernia first; if chronic I would perform colectomy and possibly later do perineal herniorrhaphy if needed. BE SURE THE ANIMAL HAS A perineal reflex and normal anal tone before doing surgery. Since many of these cats are geriatric be sure to palpate their neck well and/or consider T4 levels to make sure the animal is not also hyperthyroid.

Interestingly, several female cats have been reported with megacolon caused by extramural obstruction as a result of stricture formation following ovariohysterectomy 4-6 weeks previously. The stricture in all cases has been reported to be caused by uterine horns remaining after incomplete ovariohysterectomy.

B. Conservative/Medical Management
      1. Minimum data base, Rule out Hypercalcemia as cause(Hyperparathyroidism)
      2. Anesthesia//heavy sedation and empty colon with warm water or saline enemas. Colace or Surfak in the enema may be helpful as well as digital breakdown and removal of feces. Sponge forceps are very useful in severe cases to remove feces. Had one astute practitioner report that he successfully uses a "poole" suction tip (abdominal suction instrument) to effectively evacuate liquefied stool from the colon.
      3. High fiber diets such as W/D or R/D, R/D higher in insoluble fiber
      4. Psyllium or canned pumpkin (1-3 tablespoons per meal) has been recommended
      5. Petroleum jelly used by some clinicians as a laxative
      6. Lactulose favored by some clinicians (but not cats!) 1 ml per cat q8-12h
      7. Cisapride (0.5 mg/kg) or a total of 2.5-10 mg q8h or q12h may be successful and should be used concurrently with Lactulose. Available through compounding pharmacies.

Inevitably, many animals with megacolon begin to have episodes of obstipation closer and closer togeher and the owner, cat, and veterinarian tire of anesthetic episodes etc. If you sense the case headed this way and MOST do, consider saving the owner, cat, and you from further episodes and recommend surgery.