Megacolon

Megacolon is a condition of the colon (last part of the intestine before the rectum and anus) where it becomes irreversibly stretched. This can be secondary to a prolonged obstruction which prevents feces being passed through the anus or in association with nerve disorders or diseases causing weakness of the muscles in the colon.

Constipation is the main clinical sign of megacolon as the dilated colon gradually impacts with feces. This can result in associated signs of loss if appetite, vomiting and weight loss. Some cats will be seen to strain as a result of the constipation however this is not always present and owners may only notice a lack of feces in the litter tray.

The condition is usually diagnosed when the abdomen is palpated (felt) during a physical examination of the cat. This can be confirmed by x-ray.

Nerve disorders are most commonly spinal or pelvic injuries. Other less common causes include spina bifida, and dysautonomia (Key-Gaskell syndrome).
Conditions associated with muscle weakness include hypokalemia (low potassium), hypercalemia (high calcium), uremia (high urea in blood generally secondary to kidney failure), and hypothyroidism (low thyroid hormone)

Obstructions can be around the colon as with fractures of the pelvis, prostate swelling, and tumors within the pelvis. Blockage within the colon and rectum can include bones, hair and tumors or polyps. Perineal hernia can lead to the formation of a diverticulum (sack) in the rectal wall which can become impacted resulting in obstruction.

Pain and even environmental factors such as dirty litter trays can cause obstipation ( refusal to void feces).

In many cases megacolon is idiopathic (no predisposing cause can be found).

Treatment of megacolon will usually require administration of an enema. Dehydrated cats should be treated with fluid replacement before being anethetised. Medication to correct any underlying cause and prevent further impaction should follow. A range of laxative preparations are available including lactulose and psyllium fiber. Drugs which stimulate colonic contractions such as cisapride can be beneficial. Dietary management involves a high fiber diet with high digestibility.

Some cases are not able to be controlled with medical management and will require surgical removal of the affect length of colon. Cats generally respond well to this surgery although the feces may be unformed for a period of up to 6 months while the remaining intestine adapts to perform the water absorbing function of the colon.