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Feline Urologic Syndrome

Randy Walker DVM

About Feline Urologic Syndrome...

Feline Urologic Syndrome (abbreviated F.U.S.) is a condition of cats in which crystals are formed in the bladder. These crystals tend to clump together and form plugs which often obstruct the urethra (which is the passageway from the bladder to the outside) leading to a serious and often life threatening situation.

What Are The Clinical Signs Of F.U.S.?

The most common signs are difficulty urinating, being unable to urinate at all, cystitis (inflammation of the bladder), bloody urine passed in small amounts, urethral obstruction (in male cats), loss of appetite, lethargy, and vomiting due to the buildup of toxins in the bloodstream. When total obstruction of the urethra occurs the patient can die from this buildup of toxins in the system.

What Causes Feline Urologic Syndrome?

What actually causes F.U.S. to occur in the first place is still poorly understood but is being studied. The main factors that cause the crystals to form are (1) magnesium in the diet, and (2) pH of the urine.

Why Is The Magnesium Content Of The Diet Important?

The crystals which are formed (called Struvite crystals, Triple Phosphate crystals, Magnesium-Ammonium-Phosphorus crystals, or MAP crystals) contain magnesium as one their main ingredients. So when you have a cat who has F.U.S., they will produce more crystals when the diet is high in Magnesium and less crystals when the diet is low in Magnesium.

Why Is The pH Of The Urine Important?

The struvite crystals will dissolve in urine with an acidic pH and will crystallize in urine with a basic pH.

So What Kind Of Diet Is Best For The Patient With F.U.S.?

The F.U.S. patient should be maintained on a diet which is low in Magnesium and which causes the urine to have an acidic pH. There are several diets on the market which do this.

How Is F.U.S. Diagnosed?

In addition to the history and physical exam, we diagnose F.U.S. by detecting the struvite crystals in a urine sample. Also, in most cats who have urinary obstruction from the urethral plug, the distended bladder can be easily felt upon abdominal palpation (meaning to feel diagnostically).

How Is F.U.S. Treated?

This depends of whether the F.U.S. patient has the urethra obstructed or not. Many male cats have a complete obstruction of the urinary bladder upon admission and in these cases we give the patient a mild gas anesthetic and then "unplug" the urethra by gently flushing the plug out with a urinary catheter and saline solution. Then, in critical cases (and most of them are) we will suture the catheter in place to allow good drainage of the bladder while we use medications to get the condition under control over the next 3-4 days. Many of these cats have a backup of toxins into their bloodstream and must be given I.V. fluids to flush the toxins from their system. In the vast majority of these cases there is also a bacterial infection of the bladder and we give antibiotics to treat this. These cases usually require a substantial amount of nursing care to get the bladder cleaned out. In those cases where the urethra is not obstructed with a plug of crystals, we usually try to manage the case medically using antibiotics, a low magnesium diet, and urinary acidifiers either given separately or in the low magnesium diet. The rationale here is that it is not to the patient's advantage to "unplug" them unless they are "plugged" to begin with. It should be noted that, of the male cats presented with unobstructed F.U.S., about 50% of them will "plug" before we can get the crystals under control and therefore need to be ''unplugged" so this should be watched for. But it is usually not a good idea to "unplug" a tomcat unless he is "plugged". To "unplug" a tom cat who is not "plugged" does him no service and only subjects the urinary tract to unnecessary trauma. If the tom cat does "plug" (or obstruct) before we can get the crystals dissolved medically (and it does often take at least several days) then he will need to be unplugged as soon as possible.

If My Cat Has An Unobstructed Case Of F.U.S. And Is Not Treated, What Would Be The Most Likely Outcome?

The condition will worsen, and, especially if its a male cat, the urethra will most likely obstruct ("plug"). Without emergency treatment the cat will most likely die of renal toxicity or a ruptured bladder or both.

Which Cats Are Most Likely To Get Feline Urologic Syndrome?

F.U.S. appears to affect males slightly more than females and usually attacks between the ages of 2 and 8 years. The severe, most noticeable clinical signs are noted in neutered male cats. We see F.U.S. more often in neutered male cats for several reasons, the main one being that the vast majority of adult male cats we see are neutered. There is no hard evidence that neutering induces F.U.S. Feline Urologic Syndrome occurs in both male and female cats and the main difference in the disease produced is due to the differences in the urethra of each sex. In females the urethra is short, relatively wide, and makes a "straight shot" to the outside. For this reason the crystals are less likely to clump together as plugs and the patient is less likely to obstruct. In males the urethra is much longer, very narrow, and follows a winding, tortuous path to the outside. This gives several areas where clumps of crystals can accumulate and cause an obstruction.

How Is F.U.S. Prevented?

Most cats who are on a low magnesium diet which causes the urine to become acidic will not have a recurrence of F.U.S.

What Is The Likely Outcome If The F.U.S. Cat Does Not Stay On The Low Magnesium/Low Urine pH Diet?

If the cat goes back on regular cat food there is at least an 80% chance that crystals will appear again in the urine, leading to cystitis (inflammation of the bladder) and obstruction ("plugging"). The F.U.S. cat should stay on the low magnesium/low urine pH diet and water and nothing else. Treats, table scraps, etc. will defeat the purpose of the diet and promote F.U.S.

Is It True That Some Cats Will Continue To Produce Crystals And Can Obstruct, Even On The Low Magnesium/Low Urine pH Diet And What Can Be Done For These Cats?

A small percentage of cats (approximately 1 out of every 30) will continue to produce crystals, even on the low Magnesium/low urine pH diet and for these cats surgery is recommended to straighten and widen the urethra. Although this used to be the only treatment available for F.U.S., we now are able to avoid surgery in the vast majority of cats and only about 3% will need surgery.


- Randy Walker DVM
Sun Lakes Animal Clinic
May 16,2004



"Until one has loved an animal, a part of one's soul remains unawakened."
- Anatole France, 1921 Nobel Prize Speech -


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