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Megacolon
is a condition of extreme and irreversible dilation and poor motility of
the colon, usually combined with accumulation of fecal material and the
inability to evacuate it. The majority of cases (62 percent) have no known
cause, however, disorders that lead to recurrent episodes of constipation
can also result in megacolon. For
years, there was debate as to whether the problem was neurological vs.
muscular, however, recent studies have now shown that cats with megacolon
have an impairment of the colonic smooth muscle.
Constipation is a clinical sign characterized by absent, infrequent or
difficult defecation associated with retention of feces within the colon
and rectum. There are many potential causes of constipation, for example:
obstruction of the colon due to a foreign object, tumor or stricture, bone
impaction, neurologic disease, or pelvic canal narrowing due to pelvic
fractures. Most cats respond with medical therapy but some have recurrent
episodes, leading to obstipation. Obstipation occurs when the colon
becomes so severely impacted with a large amount of hard feces that it is
completely impossible to defecate. The
longer the feces remain in the colon, the more fluid is extracted by the
colonic lining, resulting in a progressively drier and firmer fecal mass.
Repeated episodes of constipation or prolonged obstipation can lead to
megacolon.
Diagnosis of Megacolon
Causes and Risk Factors
Causes
Most cases of megacolon (62 percent) are idiopathic (they occur for no clearly defined
reason). Other causes include pelvic canal narrowing (23 percent),
neurologic injury (6 percent), and as a condition in Manx cats born with
sacral spinal cord deformity (5 percent). Other potential causes include
colon cancer or complications associated with previous colon surgery.
Risk factors
Age – Megacolon is most
often seen in middle-aged
cats with an average age of 6 years.
Breed/genetics – Domestic
shorthaired cats are most often affected (46 percent). It has been found that 12 percent of cases are
Siamese. Megacolon can also occur in Manx cats with sacral spinal cord
deformity.
Sex – Megacolon is more
common in males (70 percent) than females.
Other medical disorders –
Cats with recurrent episodes of constipation or disorders that lead to
constipation are more at risk of developing megacolon.
Prevention – Prevention of megacolon can be difficult. The
underlying cause must be eliminated, if possible. Cats prone to
constipation may benefit from a fiber-supplemented diet, laxatives and/or
enemas. To add fiber to the diet, you can administer psyllium (Metamucil
powder) at a dosage of 1 to 2 teaspoons per meal, wheat bran (1 to 3
teaspoons per meal) or canned pumpkin (1 to 3 teaspoons per meal) added to
the food once a day. (Many cats actually like the taste of canned
pumpkin). Manhattan Cat
Specialists has a veterinary fiber formulation called Vetasyl that works
well in constipated cats. In
addition to adding fiber, laxatives may be necessary. Commonly used
laxatives include white petrolatum (Laxatone) or lactulose. Manhattan Cat
Specialists keeps a supply of these medications available at all times.
Clean fresh water should be available at all times.
History and Clinical Signs
Presenting signs and
historical problems – Straining to defecate, painful defecation, blood
in the stool, passage of small amounts of dry, hard feces or absence of
feces are common signs of megacolon. Most often, cats have a history of
repeated episodes of constipation. Other
systemic signs of illness may be present as a result of prolonged
inability to defecate, such as anorexia, lethargy, weight loss, abdominal
pain and vomiting.
Physical Examination
Findings
General
Attitude – Most affected
cats have a normal attitude but those with chronic untreated megacolon may
be depressed due to metabolic changes.
Body condition – Some cats
may be obese since obesity is a risk factor.
Hydration status – Cats
with chronic megacolon may be dehydrated.
Abdominal examination will
reveal a large colon full of hard feces. It may be difficult to
differentiate a megacolon from an abdominal mass without x-rays. Affected
cats may appear unkempt. Digital rectal exam may reveal a narrowed pelvic
canal, old pelvic fractures, a colonic or rectal tumor, stricture and/or
dry, hard feces.
The remainder of the physical examination is often unremarkable.
Diagnostic Studies
Special examination
techniques - Colonoscopy allows evaluation of the colon non-invasively
using an endoscope, although this is usually not necessary. The lining of
the colon can be examined for inflammation, dilations, irregularities, and
strictures. If indicated, biopsies can be obtained.
Clinical laboratory tests
– cats that may need to be anesthetized so that the feces can be
extracted manually may need blood tests performed as a pre-anesthetic
screen.
Complete Blood Count –
Usually unremarkable, although a high white blood cell count may indicate
inflammation or infection.
Serum biochemical tests –
Usually unremarkable, although some cats may have an elevated total
protein due to dehydration, or excessively low potassium or excessively
high calcium levels. Although uncommon, serum thyroxine levels should be
determined to rule-out hypothyroidism as an underlying cause.
Urinalysis – Usually
normal
Diagnostic Imaging
Radiographs (abdominal) –
Abdominal x-rays are recommended to determine the severity of the colonic
impaction and to determine the presence of any predisposing conditions,
such as foreign bodies, pelvis fractures or a mass.
Ultrasound (abdominal) –
Abdominal ultrasound is not commonly performed but may be indicated if
cancer is suspected.
Contrast radiographs – A
barium enema may be necessary if colonoscopy is not possible. This
procedure is rarely necessary.
Myelography – If a
neurologic disorder is suspected to be the underlying cause of the cat’s
condition, particularly a spinal disorder, myelography (evaluation of the
spinal cord by injecting a dye into the spinal column) may be indicated.
Pathology
Biopsy – Ultrasound guided
biopsy may be indicated if a colonic tumor or cancer is suspected.
Treatment of Megacolon
Treatment Principles
Megacolon is a dysfunction
of the smooth muscle of the colon. The goal of treatment is to maintain a
soft stool and to improve colonic motility by administering medications
that stimulate contraction of the colonic smooth muscle.
Initial/Hospital Therapy
Symptomatic therapy - The
therapy for megacolon depends on several factors including the severity of
the constipation and fecal impaction and the underlying cause. Initial
episodes of constipation, if mild, may not need any therapy at all. Mild
or moderate episodes that recur usually require some kind of treatment.
There are many treatment options. The most successful therapy usually
involves a combination of treatment interventions. Cats that are
dehydrated or have electrolyte abnormalities should be placed on
intravenous fluids to correct metabolic disorders. Once hydrated, enemas
and possible manual removal of feces can be attempted.
Enemas - Mild or moderate
episodes of constipation that recur will sometimes require the
administration of enemas. Although many cat owners are often willing and
able to administer a packaged enema to their cat at home, enemas are best
performed in a veterinary setting. Manhattan Cat Specialists uses safe,
pre-packaged enemas that work very well in cats.
If enemas are not sufficient
to remove the impacted feces, manual extraction can be attempted.
Some cats will tolerate this procedure under heavy sedation,
however, the majority will need to be completely anesthetized for the
procedure to be performed properly. It sometimes requires repeated enemas
and manual extraction to remove the majority of the feces.
Following evacuation of the
feces, laxatives and medications that increase the motility of the colon
should be prescribed.
Surgical therapy – Some
cases of megacolon respond poorly to medical therapy. In these patients, a
surgical procedure to remove most of the defective colon may be
beneficial.
Long-term/Home Therapy
Diet is an important part of therapy. There are two schools of thought
when it comes to dietary therapy. Traditionally, cats with megacolon
have been fed diet high in fiber to bulk up the feces and help attract
water to the stool, improving its consistency. This can be accomplished
in several ways. Fiber can be added to the cat’s regular diet, using
products such as Metamucil (psyllium, 1 to 2 teaspoons per meal), or a
high fiber prescription diet or over the counter diet can be fed. Wheat
bran (1 to 3 teaspoons per meal) and canned pumpkin (1 to 3 teaspoons
per meal) are other natural sources of fiber. The other school of
thought is that a colon that is having trouble propelling the stool
would benefit from a diet that doesn’t result in the production of much
stool, i.e. a highly digestible diet. The Iams Company makes such a
diet, called “Low Residue” formula, and we’ve had fairly good success
with this diet. There’s no way to predict whether a low residue or a
high fiber diet is best for any particular cat. It must be determined
through trial and error.
The occasional use of laxatives when excessively firm stool is noticed in
the litter box may be helpful. There are a variety of laxatives that can
be used.
Drugs that help the colon contract better
are often prescribed for cats with megacolon.
Cisapride is a motility drug that was recently withdrawn from the
human market, but can still be obtained for veterinary use.
Many cats benefit from this medication.
Follow-up Care
Cats with megacolon will initially require
frequent rechecks to monitor response to therapy. Owners will need to
carefully monitor their cats at home for straining, painful defecation, or
blood in the stool. Timely treatment for future constipation episodes can
help increase the quality of the cat’s life.
Prognosis
The prognosis is guarded to fair. Most cats will respond to therapy. A
few will continue to suffer from occasional episodes of constipation
that may or may not require brief hospitalization and manual removal of
feces. Some are refractory to treatment, unfortunately, and may require
surgery. However, the success rate for surgery is high and the vast
majority of cats that require surgery do well afterward.
Updated 2/9/06 |
