Megacolon

Megacolon develops gradually in most cats, with constipation progressing over weeks to months before the colon becomes irreversibly enlarged. Watch for:

• Infrequent or absent trips to the litter box for defecation (note: cats with urinary straining may be misidentified — look for whether stool is actually being produced)
• Straining to defecate with little, no, or very small amount of stool produced
• Vocalization or visible discomfort during attempts to defecate
• Small, hard, dry pellet-like stools, or liquid leaking around a fecal impaction (often mistaken for diarrhea)
• Decreased appetite, weight loss, and lethargy
• Vomiting — as the backed-up colon causes general abdominal discomfort and nausea
• A palpably enlarged, firm abdomen — sometimes the fecal mass can be felt through the belly wall
• Hunched posture or a reluctance to move

Megacolon results from long-standing colonic dysfunction. In many cats, the cause is ultimately idiopathic (unknown), but contributing factors include:

• Idiopathic megacolon: the most common form, accounting for more than half of feline cases — the colonic smooth muscle or its nerve supply is inherently dysfunctional
• Pelvic canal narrowing: old pelvic fractures from trauma narrow the channel the colon passes through, physically blocking stool; this is a treatable underlying cause
• Spinal cord disease or nerve damage: injuries or lesions that affect the nerves supplying the colon (including Manx sacral agenesis) result in poor colonic motility
• Obstructive causes: masses, polyps, perineal hernias, or foreign material that prevent normal stool passage
• Obesity: overweight cats are at higher risk for constipation and progressive colonic dysfunction
• Dehydration and low-fiber diet: chronically low fluid intake and insufficient dietary fiber make stools hard and difficult to pass, contributing to progressive stretching of the colon
• Breed: male cats and domestic shorthairs appear over-represented

A cat presented with straining and no stool production needs prompt evaluation — obstipation is painful and the longer fecal material sits, the drier and harder it becomes. Our diagnostic approach includes:

• Physical examination: abdominal palpation often reveals a large, hard fecal mass; a rectal examination assesses the rectal and pelvic anatomy
• Digital radiographs (X-rays): confirm the diagnosis, quantify the degree of colonic distension, and reveal pelvic abnormalities such as healed fractures
• Blood chemistry panel and urinalysis: assess overall health, electrolyte status (hypokalemia — low potassium — can worsen colonic motility), and kidney function before anesthesia for manual disimpaction
• Abdominal ultrasound: evaluates the colon wall thickness and rules out masses or lymph node enlargement
• Neurological assessment: for cats with suspected spinal or nerve involvement, a focused neurological exam guides further workup

Treatment is staged according to disease severity. Early-stage constipation is managed medically; advanced megacolon with a permanently dilated colon usually requires surgery for lasting relief.

• Dietary modification: increased dietary moisture (wet food, prescription GI diets) and appropriate fiber levels support colonic motility and softer stools
• Osmotic laxatives: lactulose (a non-absorbable sugar that draws water into the colon) is the workhorse laxative for feline constipation; polyethylene glycol (MiraLax) is another option tolerated by many cats
• Colonic motility enhancers: cisapride, a prokinetic drug, stimulates smooth muscle contractions in the colon and is often effective in early to moderate disease
• Manual disimpaction under anesthesia: severely constipated cats with an impacted fecal mass often require enemas and gentle manual evacuation under sedation — attempting this at home is not safe
• IV fluid therapy: dehydrated cats need rehydration before and after disimpaction
• Subtotal colectomy: when the colon is permanently dilated and no longer responds to medical management, surgical removal of most of the colon (sparing the sphincter) gives cats a dramatic improvement in quality of life. Soft to liquid stools result initially but typically firm up over several months. See Subtotal Colectomy.

A cat that hasn't defecated in 48–72 hours or is straining repeatedly without producing stool needs to be seen — this is not a wait-it-out situation. The longer feces remain in the colon, the harder they become and the more the colon stretches toward permanent damage. Dog & Cat Hospital Calabasas can radiograph, assess, and initiate treatment the same day. If your cat has already had multiple episodes, ask about a long-term medical management plan and whether a surgical consultation is appropriate. Book an appointment and let us help before the colon reaches a point of no return.