Issues

Megacolon

 

A gastrointestinal disorder characterized by persistently increased large bowel diameter associated with chronic constipation/obstipation and low-to-absent colonic motility.

 

 

PATHOPHYSIOLOGY

Acquired megacolon results from chronic colonic fecal impaction that leads to excessive absorption of fecal water and solidified fecal concretions.

Prolonged distension of the colon results in irreversible changes in colonic motility that leads to colonic inertia.

Congenital absence of colonic ganglionic cells (Hirschsprung’s disease) is not clearly documented in small animals.

The pathogenesis of idiopathic megacolon in cats likely involves a disturbance of normal colonic smooth muscle function.

 

 

SYSTEMS AFFECTED

Gastrointestinal

 

 

SIGNALMENT

Species

• Idiopathic megacolon—cat
• Acquired megacolon—cat and dog

 

 

Breed Predilections

• Some evidence for increased risk in Manx cat

 

 

Mean Age and Range

• Idiopathic megacolon—middle-aged to older cats (mean age, 4.9 years; range, 1–15 years).

Acquired megacolon—none.

 

 

SIGNS

Historical Findings

• Idiopathic megacolon—typically a chronic/recurrent problem; signs often present for months to years.
• Acquired megacolon—signs may be acute or chronic.
• Constipation/obstipation.
• Tenesmus with small or no fecal volume.
• Hard, dry feces.
• Infrequent defecation.
• Small amount of diarrhea (often mucoid) may occur after prolonged tenesmus.
• Occasional vomiting, anorexia, and/or lethargy with chronic fecal impaction.
• Weight loss.

 

Physical Examination Findings

• Abdominal palpation reveals an enlarged colon with hard feces.
• Digital rectal examination may indicate an underlying (obstructive) cause and confirms fecal impaction.
• Dehydration.
• Scruffy, unkempt hair coat.

CAUSES

• Idiopathic—cats.
• Mechanical obstruction—pelvic fracture malunion, foreign body or improper diet (especially bones), stricture, prostatic disease, perineal hernia, neoplasia, anal or rectal atresia.
• Causes of dyschezia—anorectal disease (anal sacculitis, anal sac abscess, perianal fistula, proctitis), trauma (fractured pelvis, fractured limb, dislocated hip, perianal bite wound or laceration, perineal abscess).
• Metabolic disorders—hypokalemia, hypocalcemia, severe dehydration.
• Drugs—vincristine, barium, antacids, sucralfate, anticholinergics.
• Neurologic/neuromuscular disease—congenital abnormalities of the caudal spine (especially Manx cats), paraplegia, spinal cord disease, intervertebral disc disease, dysautonomia, sacral nerve disease, sacral nerve trauma (e.g., tail fracture/pull injury), trauma to colonic innervation.

 

RISK FACTORS

• Conditions leading to inability to posture (limb and pelvic fractures, neuromuscular disease, etc.) or rectoanal pain.
• Prior pelvic fractures.
• Possible association with low physical activity and obesity.
• Perineal hernias.

 

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

• Other causes of palpable colonic masses (e.g., lymphoma, carcinoma, intussusception)—distinguish on the basis of texture, rectal examination, imaging, and mucosal biopsy.
• Dysuria/stranguria—exclude by palpation of the bladder and colon, and by urinalysis.
• Tenesmus due to inflammation of the colonic mucosa (colitis)—exclude by palpation, rectal examination, and endoscopic imaging with mucosal biopsy.

 

CBC/BIOCHEMISTRY/URINALYSIS

May show evidence of dehydration (elevated packed cell volume, total protein) and stress leukogram.

• Electrolyte abnormalities may develop depending on duration of obstipation; may be prerenal azotemia with dehydration.
• Urinalysis—no consistent changes; important to confirm normal renal function in dehydrated animals and to rule out lower urinary tract disease as a differential diagnosis.

 

IMAGING

• Abdominal/pelvic radiographs to identify any underlying causes.
• Can easily see the enlarged, fecal-filled colon on survey abdominal radiographs.
• Abdominal ultrasound may identify mural or obstructive masses.

 

 

DIAGNOSTIC PROCEDURES

May need colonoscopy to rule out mural or intraluminal obstructive lesions.

 

PATHOLOGIC FINDINGS

The most severe dilation typically occurs in the transverse and descending colon, although the entire length of the colon can be involved.

The colon is usually histologically unremarkable with megacolon.

 

 

TREATMENT

APPROPRIATE HEALTH CARE

Inpatient medical management; surgery may be indicated if recurrent/severe problem.

Medical therapy—restore normal hydration, followed by anesthesia and manual evacuation of the colon using warm water enemas, water-soluble jelly, and gentle extraction of feces with a gloved finger or sponge forceps; do not traumatize the colonic mucosa.

Continue long-term therapy at home.

 

 

NURSING CARE

• Most patients require parenteral fluid support to correct dehydration.
• Intravenous administration of balanced electrolyte solutions is the preferred route.

 

 

ACTIVITY

• Encourage activity and exercise.
• Restriction indicated in the postoperative period if surgery is performed.

 

 

DIET

• Many patients require a low-residue producing diet; bulk-forming fiber diets can worsen or lead to recurrence of colonic fecal distension.
• A high-fiber diet is occasionally helpful.
• A more palatable, maintenance-type diet can be supplemented with fiber-enriched foods (pumpkin) or products containing fermentable fiber such as Metamucil.

 

CLIENT EDUCATION

• In idiopathic disease or with severe colonic injury, medical therapy is often life-long and can be frustrating to clients.
• Increased activity of the cat with daily or alternate-day subcutaneous fluid therapy can help minimize recurrences in many cats.
• Recurrence of megacolon is common.
• Surgery (subtotal colectomy) is indicated if medical therapy fails.

 

 

SURGICAL CONSIDERATIONS

An underlying obstructive cause requires surgical correction.

Avoid enema administration/colonic evacuation prior to subtotal colectomy.

• Subtotal colectomy with ileorectal or colorectal anastomosis—treatment of choice for idiopathic megacolon refractory to medical management.
• Colectomy may also be required with obstructive megacolon caused by irreversible changes in colonic motility.

 

 

MEDICATIONS

DRUG(S) OF CHOICE

• Can improve colonic motility in less severe cases with cisapride, a prokinetic gastrointestinal drug (dogs, 0.3–0.5 mg/kg PO q8–12h; cats, 2.5–10 mg/cat q8–12h). Metoclopramide does not affect colonic motility and should not be used in cats with megacolon.
• Stool softeners (e.g., lactulose, 1 mL/4.5 kg PO q8–12h to effect) are recommended in conjunction with cisapride and diet.
• Broad-spectrum antibiotics are recommended prior to surgery to reduce the potential for bacterial sepsis.

 

 

CONTRAINDICATIONS

Sodium phosphate retention enemas (e.g., Fleet; C.B. Fleet Co., Inc.)—because of their association with severe hypocalcemia.

Mineral oil and white petrolatum—because of danger of fatal lipoid aspiration pneumonia due to lack of taste.

 

 

PRECAUTIONS

Common hairball laxatives (e.g., Laxatone, Cat-a-Lax) are typically ineffective.

 

ALTERNATIVE DRUG(S)

Docusate sodium can be used as a stool softener in place of lactulose.

 

FOLLOW-UP

PATIENT MONITORING

Following colonic resection and anastomosis—for 3–5 days check for signs of dehiscence and peritonitis.

Clinical deterioration warrants abdominocentesis and/or peritoneal lavage to detect anastomotic leakage.

Continue fluid support until the patient is willing to eat and drink.

 

 

PREVENTION/AVOIDANCE

Repair pelvic fractures that narrow the pelvic canal.

Avoid exposure to foreign bodies and feeding bones.

POSSIBLE COMPLICATIONS

Recurrence or persistence—most common.

Potential surgical complications include peritonitis, persistent diarrhea, fecal incontinence, stricture formation, and recurrence of obstipation.

Traumatic perforation of the colon is a serious complication of overzealous fecal evacuation.

 

 

EXPECTED COURSE AND PROGNOSIS

Historically, medical management has been unrewarding for the long term.

Cisapride appears to improve the prognosis with medical management in some patients, but may not suffice in severe or long-standing cases.

Postoperative diarrhea—expected; typically resolves within 6 weeks (80% of cats with idiopathic megacolon undergoing subtotal colectomy) but can persist for several months; stools become more formed as the ileum adapts by increasing reservoir capacity and water absorption.

Subtotal colectomy is well tolerated by cats; constipation recurrence rates are typically low.

 

 

MISCELLANEOUS

ASSOCIATED CONDITIONS

Perineal hernia

 

 

AGE-RELATED FACTORS

Concurrent medical conditions (e.g., chronic renal insufficiency, hyperthyroidism) may occur with idiopathic megacolon, because many cats are old.

 

 

PREGNANCY/FERTILITY/BREEDING

The effect of cisapride on the fetus is unknown.

Patients would be at increased risk for dystocia if they carried a pregnancy to term.

 

Visit your veterinarian as early recognition, diagnosis, and treatment are essential.

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