Megacolon in Cats: Severe Constipation Signs, Causes and Care

By Tailwisp Editorial TeamUpdated October 20, 20264 min read

Most cats have a bout of constipation now and then. Megacolon is something more serious. The colon is stretched, the muscle wall is weak and stool builds up, hardens and cannot be passed. Without treatment, it becomes a cycle that worsens, and cats can become very ill.

What happens in megacolon

The colon is the last part of the digestive tract, where water is absorbed and stool is formed. In megacolon, the colon becomes dilated and its muscle contractions weaken. Stool stays longer, loses more water and becomes drier and harder. The harder it gets, the more the colon stretches, and the less it works. In the most severe form, called obstipation, a cat cannot pass stool at all.

Causes

• Idiopathic megacolon. In most cats, no clear cause is found. It is thought that the muscle of the colon is affected, for reasons that are not clear.
• Pelvic injury. A fracture that healed badly can narrow the passage, causing stool to back up.
• Nerve disease. Spinal problems or nerve damage can reduce colon movement.
• Long-term constipation, for example from dehydration or kidney disease. See constipation in cats and chronic kidney disease in cats.
• Tumors or narrowing in the colon or rectum.
• Painful anal or hip conditions.
• Dysautonomia and other rare conditions.
• Litter box avoidance, which causes cats to hold in stool. See cat litter box aversion.
• Obesity and low activity.

Signs

• Straining in the litter box with little or no stool.
• Small, dry, hard stool pieces.
• Crying while trying to pass stool.
• Passing stool outside the box. See why does my cat poop outside the litter box.
• Vomiting, loss of appetite and lethargy.
• A firm, tubular mass felt in the belly.
• Small amounts of liquid stool leaking around a blockage, which owners may mistake for diarrhea.
• Weight loss and dehydration.

Warning: A cat, especially a male, that strains and produces no urine may have a urinary blockage, which is an emergency. See signs of a urinary blockage in cats.

Diagnosis

The vet will palpate the belly, and take X-rays to show a stool-filled, enlarged colon. Bloodwork checks hydration, kidney function and electrolytes. Further tests can look for the cause, such as spinal X-rays or colon exams.

Treatment

• Rehydration. Intravenous or subcutaneous fluids soften stool. See how to give a cat subcutaneous fluids.
• Enemas and manual removal, under sedation or anesthesia, done by the vet. Never give a cat a human enema, because some are toxic.
• Diet. Increase water intake, and in some cases use a higher-fiber or highly digestible diet, as advised by your vet. See wet vs dry cat food.
• Medication. Stool softeners such as lactulose or polyethylene glycol, and drugs that stimulate colon movement, such as cisapride, may be prescribed.
• Weight loss, for overweight cats. See how to help an overweight cat lose weight.
• Surgery. When medical treatment fails, subtotal colectomy, removal of most of the colon, can be done. Many cats do well afterwards, though stool may be softer for some time.

Home care

• Encourage drinking with fountains and wet food. See cat water fountains: worth it.
• Keep litter boxes clean and accessible. See how often to clean a litter box.
• Encourage play and exercise. See exercise for indoor cats.
• Give medication exactly as prescribed.
• Monitor stool, and report changes.

Outlook

With early treatment, many cats do well for years. Idiopathic megacolon often needs lifelong management. Delay can lead to a severe, hard-to-treat disease.

What happens after surgery

Cats that have a subtotal colectomy usually have soft or loose stool for several weeks, which gradually firms up in most. Your vet may advise a highly digestible diet and sometimes fiber. Most owners report that their cats are much happier afterward, with normal appetite and energy. As with any surgery, there are risks, including infection and leakage from the surgical site, so follow instructions and watch the incision.

Preventing repeated episodes

Because megacolon often returns, early treatment of any constipation is important. At the first sign of straining, small hard stool or reduced stool output, contact your vet. Keep a record of how often your cat passes stool, and weigh regularly. Keep stress low, and make sure the litter box is clean, easy to enter and in a quiet place. See where to put the litter box.

Medications to avoid

Never give your cat human laxatives, mineral oil by mouth or phosphate enemas. Some are dangerous and can cause serious illness or death. Always ask your vet before giving any supplement or remedy, even natural ones such as pumpkin, since the dose and suitability matter. See can cats eat pumpkin.

When to see a vet

See a vet if your cat strains, passes no stool for more than a day or two, or vomits. Use the US vet directory to find a clinic.

This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.