Description

The colon or large intestine contains the remains of digested material

and dehydrates it to form feces. The colon ends at the rectum

and anus. If the passage of feces is altered or delayed and feces

remain in the colon for prolonged periods, the colon continues to

extract water from the feces. As a result, the feces becomes very dry

and hard, which makes it harder for them to move. Subsequently,

more and more feces accumulate, which stretches the colon and

greatly increases its size. A chronically enlarged colon that is often

filled with dried feces is called a megacolon .

Causes

Of the two main causes of megacolon in cats, the more common

one is unrelieved or recurrent constipation. Constipation may arise

from narrowing of the pelvis due to an old fracture, paralysis of the

anal region from neurologic damage or disease, chronic intestinal

diseases, or other diseases that cause persistent dehydration (such

as kidney disease). If constipation is not relieved, the distended

colon loses normal muscle strength, which further aggravates the

constipation.

A second form of megacolon develops from loss of normal

nerve function within the wall of the colon. The nerve problem

decreases muscle strength, which leads to constipation.

Constipation is an effect, not a cause. The cause of the nerve dysfunction

is not often identified. Regardless of the underlying cause,

the end result is a colon that is dramatically larger than normal.

Clinical Signs

The most common sign is severe constipation. Cats may strain for

long periods in the litter box, passing only small amounts of feces.

Some cats vomit and lose their appetite. Occasionally, a liquid part

of the feces is passed (paradoxical diarrhea), while solids are left

behind. On clinical examination, an enlarged colon often can be

felt within the abdomen. The cat may have signs of dehydration

(tacky mucous membranes, stiff skin that tents up when pulled).

Diagnostic Tests

X-rays of the abdomen and spine are often recommended to look

for problems in the skeleton (such as old pelvic fractures), to

assess the degree of constipation, and to search for other problems

that may be contributing to constipation. Routine laboratory tests

and an abdominal ultrasound are sometimes recommended to look

for contributing diseases and evidence of dehydration.

In most cases, it is important to correct any dehydration with subcutaneous

(under the skin) or intravenous fluids prior to treating

the constipation. This is particularly important if the cat has kidney

disease. Treatment of the constipation and megacolon involves

several options. The approach taken depends on the cause of the

disease. Treatment options include the following:

• Relief of severe constipation often requires general anesthesia

and administration of multiple enemas to soften the fecal material,

combined with manual kneading and extraction of the stool.

Multiple rounds of anesthesia and administration of enemas

over several days may be needed to relieve the constipation.

• In cats with less severe constipation (particularly if they can

still pass some feces), warm-water enemas, drugs (such as cisapride,

nizatidine, ranitidine) to increase muscular contraction

of the colon, laxatives (such as lactulose, docusate sodium),

and dietary changes (increased fiber) may be tried.

• If constipation arises from a mechanical problem, such as an

old pelvic fracture that is impeding passage of feces, surgery

may be needed to enlarge the pelvic canal.

• For colons that have lost all muscle strength and ability to

move feces, partial removal of the colon (subtotal colectomy)

may be considered. Your veterinarian may refer your cat to a

veterinary surgery specialist for this procedure.

Follow-up Care

Cats that are treated with medications and laxatives are usually monitored

closely with follow-up visits until the constipation has resolved.

Long-term preventive medical therapy and periodic rechecks are

often advisable, because constipation can recur. After subtotal colectomy,

the initial postoperative period can be challenging, because

bowel movements may be soft for a period of time. Eventually their

consistency often returns to normal. Medical therapy is not often

needed after surgery, but periodic rechecks may be recommended.

Prognosis

Prognosis for cats with megacolon that are treated medically is usually

guarded (uncertain). If muscle function returns and constipation

resolves with therapy, the prognosis is reasonable; however, recurrence

is common in many cats. Cats can suffer severe, life-threatening

illness as a result of long-term constipation. The prognosis for

recovery from surgery is good if no complications occur.

Treatment Options