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Constipation and Megacolon

Megacolon is the condition where the large intestine (colon) is associated with chronic constipation/obstipation with minimal colonic motility. The colon normally receives the remains of the digested material of food from the small intestine and then absorbs the water from this material before passing the dehydrated matter (faeces) to the rectum and anus to pass out.

If the colon has reduced motility, then the passage of faeces is delayed resulting in even more water being extracted from the faecal matter than usual causing the faeces to become very hard and dry. In addition to the decreased motility of the colon, the very dry faeces make the material even harder to move.

If the condition persists for some time, often the faeces will accumulate causing a large amount of dry material in the colon causing it to increase a lot in size and its walls to stretch.  Prolonged stretching of the colonic wall will result in irreversible changes leading to a chronically enlarged colon filled with dried faeces called a megacolon. This is very similar to a balloon that has been blown up beyond a certain size causing it too lose its elasticity and never return to its original small shape.

The most common cause of megacolon is an unrelieved or recurrent constipation. Constipation can be due to a variety of reasons such as dehydration (e.g. secondary to kidney disease), chronic intestinal disease, anal disease or narrowing of the pelvis. A distended colon may lose the normal muscle strength further aggravating the constipation.

Another common cause of megacolon is a loss of normal nerve function within the colonic wall leading to decreased muscle strength. Any of these causes will lead to the same result of a dramatically larger colon blocked with faeces.

Sometimes, the condition can be exacerbated during periods of stress such as introduction of a new animal or absence of the owner.

Clinical signs

Affected cats will often exhibit signs of severe constipation, such as straining in the litter box for long periods, passing no or only very small amounts of faeces. Some cats will cry in discomfort. Others may become inappetant and even vomit. Many of these cats are dehydrated.

Diagnostic tests

Physical examination will often reveal dehydration (stiff skin on feeling) and an enlarged colon packed with faeces when feeling the abdomen. X-rays can help assess the severity of the constipation. Blood tests and ultrasound scans may help to reveal any contributing factors or diseases such as kidney disease.


In almost all cases, it is important to correct the dehydration by either subcutaneous or intravenous fluids. Several options are available to treat the megacolon and constipation, which may include:

·      Drugs to aid the motility of the colon by improving the muscle contractions such as cisapride (not easily available anymore).

·      Laxatives such as lactulose to help soften the stools.

·      Micro-enemas in less severe cases, may aid the passage of stools. In more severe cases, general anaesthesia may be required to facilitate giving a warm soapy enema, extraction of the stool and manual breakdown/kneading of the stool.

In very severe cases, where the colon has lost all muscle strength and motion, surgery may be required. The surgical procedure is called a subtotal colectomy and involves removing part of the colon. Although we can perform this surgery at Acorn hospital if necessary, we will often try to avoid it as there are many potential complications involved with this procedure(which can be fatal).

Long term management involves changing the diet. Initially, increased dietary fibre can be helpful but in the latter stages of the disease, a low residue producing diet is preferable as less faeces will be produced meaning less chance of constipation. We also recommend wet diets in preference to dry food, to minimize the likelihood of dehydration. Water fountains and regular subcutaneous fluids can also help to prevent dehydration.

Minimising stress by feeding cats separately in multiple cat households and having separate and regularly cleaned litter trays for each cat can help. Also pheromones such as Feliway may also be beneficial. Megacolon is a chronic condition and  it is important to remember that it will often recur.