Feline Health
Caring for Cats
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A Winn Feline Foundation Health Article On ...
Feline Bladder Stones and Urinary Obstructions
by Susan Little DVM, Diplomate ABVP (Feline Practice)
A urolith is stone-like object that can be found in the bladder and, less
commonly, in the kidney, of cats. Some studies have shown that up to 13%
of cats with lower urinary tract disease today have uroliths. They can be
present without causing any symptoms in the cat, but they are very often
associated with hematuria (blood in the urine), pollakuria (increased
frequency of urination) and dysuria (difficulty passing urine). Many cats
will attempt to urinate outside of their litterbox. In some cases,
uroliths can cause partial or total obstruction of the urethra (the tube
leading from the bladder outside the body), so that little or no urine can
pass. Obstructions are often emergency situations for the cat, causing
great pain and endangering its life. Owners may see their cat visiting the
litterbox frequently and straining and erroneously believe the cat is
constipated.
Uroliths are formed of minerals plus some organic material (usually
mucus-like). Cats can
have several types of uroliths, but the two most common types are struvite
(magnesium ammonium phosphate or MAP) and calcium oxalate. In the past,
the most common urolith type was struvite. However, in the last ten years,
the number of calcium oxalate uroliths has increased so that now the two
types occur with almost equal frequency. This is suspected to be due to
changes in feline diet formulations, for the acidic diets that discourage
struvite uroliths can actually encourage calcium oxalate uroliths to form
in some cats.
Struvite uroliths can be found in both male and female cats, but female
cats seem to be at higher risk. The highest risk cat is the female aged 1
to 2 years old. The mean age for all affected cats is 5 years, but kittens
as young as 1 month old and cats as old as 20 years have been found to
have struvite uroliths. When struvite uroliths are present in kittens
under 1 year old, a bacterial infection is often the underlying cause. In
older cats, bacterial infections usually do not play a role.
Calcium oxalate uroliths affect males a bit more frequently than females.
The risk for this type of urolith increases with age - the patient with
the greatest risk is the 10 to 15 year old neutered male cat. Calcium
oxalate uroliths seem to occur more frequently in the Persian, Himalayan
and Burmese breeds. At least one study is currently ongoing to investigate
why this is so. Bacterial infections are usually not associated with
calcium oxalate uroliths.
Management and prevention of uroliths depends on the type of urolith and
the presentation of the patient. If a cat is experiencing a partial or
total obstruction, emergency treatment to relieve the obstruction is
required. Cats with urinary obstructions are often dehydrated, have
electrolyte and acid-base imbalances, and have increased levels of waste
products in their bloodstream. These problems can lead to heart and kidney
dysfunction as well as bladder damage, and even death if left untreated.
Typically, the urethra is catheterized to restore flow of urine and fluid
therapy is started. Blood and urine tests are done to determine the
patient’s status and guide further treatment. After the patient is
stabilized, further tests are done to ascertain if uroliths are present.
 Many uroliths can be detected by x-rays. Single or multiple uroliths may
be present. However, some do not show up well on x-rays or they may be too
small to be seen. Feline uroliths are often flattened, much like the shape
and size of a dime, although they can be pebble-like as well. In some
cases, a bladder ultrasound can be the best method of detection. In other
cases, or where ultrasound is not available, special x-rays may be done
that involve injecting a contrast agent (such as a dye) into the bladder
in order to see the stone more clearly. It is interesting and important to
note that a routine urinalysis will not show any signs of uroliths in the
bladder in up to 50% of cases.
It can be very difficult to tell what type of urolith is present in a
patient from an x-ray or an ultrasound. It takes removal of the urolith
and analysis by a laboratory to determine this for sure. Struvite uroliths
can often be dissolved with a therapeutic diet called Feline Prescription
Diet s/d (by Hill’s). It can take up to 4 months of feeding this diet
exclusively to dissolve the urolith. During this time, the original
symptoms of the problem may still occur. Calcium oxalate uroliths cannot
be medically dissolved. For this reason, many owners opt for surgical
removal of uroliths. This has the advantage of correct identification of
the urolith type (which is important to prevent recurrences) and a quicker
resolution of the problem for the cat. In some cases, small uroliths can
be flushed out when the bladder is catheterized and they should be saved
for analysis.
Cats who have had a urolith are always at risk for future occurrences.
However, struvite and calcium oxalate uroliths can both be prevented in
the future by dietary management. It is critical to note that they require
different types of diets. Struvite management diets typically help to
produce an acidified urine, while calcium oxalate management diets produce
a slightly alkaline urine. There are several commercially prepared diets
on the market for each type of urolith. Before acidified diets were
available, cats were given an acidifier in pill or gel form in order to
acidify their urine. Dietary therapy is a safer way to accomplish this,
and under no circumstances should cats on an acidifying diet also be given
a supplemental acidifier. It is also important to note that cats who have
kidney disease are not good candidates for acidifying diets.
Antibiotics are only used if it was determined a bacterial infection was
part of the problem (which is uncommon) or if the patient required
catheterization to relieve an obstruction. Occasionally, cats with calcium
oxalate uroliths may need other measures in addition to prescription diets
(such as some prescription medications) to prevent recurrences. In
general, canned diets do a better job of preventing future occurrences of
uroliths because they encourage more water consumption than dry diets.
References:
- Menrath V. Problem plumbing ! Journal of the Feline Advisory Bureau, Vol
36, Spring 1998, pp. 21-24
- Osborne CA et al. Changing demographics of feline urolithiasis:
perspectives from the
Minnesota Urolith Center, in August JR (ed): Consultations in Feline
Internal Medicine 3,
WB Saunders, Philadelphia, pp349-360, 1997
- Osborne CA et al. Diagnosis, medical treatment, and prognosis of feline
urolithiasis. Vet Clinics of North America, Small Animal Practice, Vol
26(3): 589-627, 1996.
Please Note: The Winn Feline Foundation provides the feline health
information on this site as a service to the public. Diagnosis and
treatment of specific conditions should always be in consultation with
one's own veterinarian. The Winn Feline Foundation disclaims
all warranties and liability related to the veterinary advice and
information provided on this site.
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