The wacky world of bladder stones – Episode 2

The wacky world of bladder stones – Episode 2


April 3, 2014


From the Desk of Dr. Voorheis


When last we spoke, we had reviewed the pesky business of bladder stones including types of stones as well as the process of diagnosis and a brief overview of treatment options. Here in Episode 2, I will address treatment options for specific stones in greater detail as well as share the story of Feline Lower Urinary Tract Disease or FLUTD.  Yes, my cat clients finally have a blog to call their own!  

On a personal note, I hope you are all well and that the recent earth moving events caused no problems for you. I know that a few of our clients had damage to their homes. I wish you all the best as we all may be a little hypersensitive to rattles and vibrations. I was typing in the dark this morning at the kitchen table when one of my cats jumped on the table to help (of course). This caused the table to vibrate and I jumped about 3 feet. No kidding. Anyway, back to these pesky stones.

There are two basic principles of treatment for bladder stones. The first is the relief of any urethral obstruction. We do this through passing a small catheter around the stones, tapping into the bladder to relieve pressure on the bladder, or dislodge the urethral stone by moving it back into the bladder. This process is called retrograde hydropulsion. Rarely, an emergency urethrotomy is necessary. A urethrotomy is a surgical procedure where an incision is made into the urethra to relieve the urinary obstruction. Decompression of the bladder may also be necessary.  The second option for dogs who are obstructed is that they may require emergency relief of their obstruction. Those dogs need IV fluids, electrolyte monitoring and correction. Sometimes electrolytes can be so disturbed that it causes heart problems. Heart problems because of an obstructed bladder?  Yes!   More commonly, an obstructed urinary tract shuts down kidney function resulting in signs consistent with acute renal failure. In this instance, treatment is initially directed at life saving measures prior to stone removal or dissolution attempts. 

 After the initial clearance of urethral obstruction, we arrive at a place where more decisions need to be made. The reality faced by most veterinarians who see dogs and cats with bladder stones is that in most instances we don’t know what the chemical composition of the stone is. In order to treat the animal in a non surgical way, we need to have that information. Sometimes if the stones are small enough we can use a procedure called “Urohydropropulsion” to push some of the stones out of the urinary tract. More often than not the stones are too big to be pushed out of the bladder. There are some cases and some types of stones where the stones are of various size and we can get enough for a diagnosis prior to surgery.  In those instances we may be able to avoid surgery if the stone is amenable to dissolution. I am often asked if it is cheaper to avoid surgery by medical dissolution. The answer is no. Dogs undergoing medical dissolution will require multiple trips to the veterinarian for urinalysis, radiographs to monitor progress, and bacterial cultures. That being said, remember that every case is unique and a treatment plan will be specific for the individual animal. At WBAH, we do not practice cookie cutter medicine.

 When we do not know the chemical composition of the stone, the animal will require a surgical procedure called a cystotomy. In MANY cases, even if we do know the chemical composition of the stone, surgical removal is still the best choice for relieving the problem. Once we know what stone type we are dealing with, our job is to try and prevent stone formation. In general, whether we have managed the stone by medical dissolution or surgical removal, prevention is directed to the induction of diuresis (dilute urine) and the eradication of urinary tract infections. Giving dogs an opportunity to void frequently and performing frequent urinalysis to monitor for urine pH, crystals and bacteria should be done. Preventing stones is certainly an ongoing effort.  

 So what kind of non surgical options do we have based on knowing what type of stone we are dealing with? Well, let’s break that down.

Struvite uroliths (stones)

These are stones made up of magnesium-ammonium-phosphate and often referred to as triple phosphate stones. These stones are often associated with bladder infection.  By performing a urinalysis and culture, we can get hints that it may be a struvite stone. If the animal has a UTI (urinary tract infection) confirmed by a culture and the owner wants to try medical dissolution, struvite stones may be dissolved by feeding a struvite dissolution diet I recommend Hill’s Canine Prescription Diet S/D or Royal Canin canine URINARY SO.  On average, it takes two to three months to dissolve struvite stones using this method but the range can be as little as two weeks to as much as 7 months. The animal’s UTI must be controlled during this time or the dissolution won’t work, or certainly won’t work as well. In addition, dogs with medical conditions such as congestive heart failure, hypertension and certain kinds of kidney disease can’t be feed the stone dissolution diets. Many Miniature Schnauzers can’t be fed the stone dissolution diet because the diet has a relatively high fat content and they are prone to developing pancreatitis which can be caused by eating diets high in fats. The key to dissolving struvite uroliths is preventing or treating infection and feeding the dissolution diet EXCLUSIVELY.

 Calcium Oxalate Uroliths (stones)

There is no diet to dissolve oxalate stones. So their treatment is always surgical removal. A diet of restricted protein, moderate restriction of calcium, sodium and oxalate with a normal intake of phosphorus, magnesium and vitamins C and D, is recommended to prevent recurrence of calcium oxalate stones. The prescription diet we most often recommend is Hill’s Prescription diet u/d. The issue with this diet is that some dogs don’t like it. I’ve recently been working with certain recipes for home cooked diets to provide an alternate option. In addition, potassium citrate given orally helps prevent recurrence of oxalate stones. Citrate complexes with calcium and forms a relatively soluble calcium citrate and in the right dose causes mild alkalinization of the urine pH. BUT, if we make the urine pH to alkaline we end up forming a different kind of stone. So this stuff takes monitoring of the urine, i.e. frequent urinalysis. Lastly, I add thiazide diuretics to decrease urinary excretion of calcium and to help form dilute urine. Both are key in preventing stone formation. 

Urate Uroliths (stones)

Urate stones are relatively rare. They are seen most often in Dalmatians, English Bulldogs and in dogs with certain types of significant liver diseases. Dalmatians and some English Bulldogs have a defect in the liver transport of uric acid. Uric acid is a product of purine metabolism. Uric acid is not converted to allantoin which is soluble in urine. Uric acid is not soluble in urine. The stones that form are ammonium acid urate stones. These stones also develop with increased frequency with urinary tract infections because many UTIs increase urine ammonia concentrations. The goals in trying to dissolve urate stones are feeding a low protein diet, giving a medication called allopurinol which decreases the formation of uric acid, controlling UTIs and sometimes giving potassium citrate to balance urine pH. A low protein diet is a key. The recommended diet is Hill’s U/D. Too high of a protein diet in dogs who take the medication allopurinol can result in a stone called a xanthine stone.  These dogs are complex and require continual management. The dogs who develop these stones that are caused by their hepatic insufficiency have even more trouble. We must try to correct the underlying liver disorder if possible. If we can improve hepatic function, the stones may spontaneously dissolve. 

 Silicate Uroliths (stones)

There are no known ways to dissolve silicate uroliths. After surgical removal, diets to increase urine volume and alkalinization are recommended. So prevention is similar to that recommended for calcium oxalate uroliths (Hill’s canine U/D, potassium citrate, thiazide diuretics).  Oh, and don’t let them eat soil. In some parts of the country, silicate can be found in soil, so it’s best not to take a chance with these dogs. 

 Cystine Uroliths (stones)

As with many of the above stones, dissolving or preventing cystine stones includes a protein reducing diet, alkalinization of the urine and administration of thiol-containing drugs. Again, Hill’s U/D is the appropriate diet. Keeping the urine alkaline using Potassium Citrate is indicated too. There are two possible medications to use to try to prevent cystine stone formation.  Both complex with cystine and the resulting product makes cystine much more soluble in the urine. Of the two, d-penicillimine and N-2mercaptopripionyl-glycine a.k.a MPG, MPG has fewer side effects. 

 The key to prevention of recurrent stones is monitoring the urine. Monthly urinalysis to check for UTI, stone formation and urine pH is key. If the urinalysis suggests UTI, a culture should be performed. After stones have been removed, the next goal is to prevent them from coming back. Too often, we take a sigh of relief, and think we are done. But continuing to monitor is crucial in the prevention of new stones.  

“Ok, wait a minute doc. Didn’t you promise us something about cats and urinary tract something or another? Well, yes I did! So now let’s talk about Feline Lower Urinary Tract Disease or as we call it…FLUTD. After all, bladder stones and urinary tract infections et all…’s all living in the southern region of the animal. Partners in crime if you will. 

 So what is this FLUTD thing anyway? The signs of feline lower urinary tract disease are frequent urination, blood in the urine, difficulty or straining to urinate, inappropriate urination and partial or complete obstruction. It is equally common in females and males and overweight animals are at higher risk. These are typically young to middle aged cats and it is seen more often in winter and springtime, although it can be seen at anytime of the year. It is also seen more often following rainstorms, even in indoor cats. Go figure that one! The worst thing about FLUTD is that it can be fatal. I will explain this more in a moment, but please know that cats can die from their lower urinary tract disease. It’s no joke. 

 strained cat                

 There are a number of ways to try to get a handle of FLUTD. It can be divided into two broad categories based on the presence or absence of an identifiable cause of the lower urinary tract signs. As clinicians, we examine an animal and quickly identify the FLUTD as either obstructive or non-obstructive.Obstructive is always a life threatening emergency which requires immediate treatment.  Identifiable causes of FLUTD include urinary tract infections, anatomic abnormalities (defects in the bladder wall or urethral strictures), trauma, irritant cystitis, neurologic disorders, behavioral disorders and neoplasia and uroliths (stones! Partners in crime as I said!) can all mimic FLUTD.  However, in many cases despite a thorough check, the cause for the FLUTD is classified as idiopathic (unknown).

 FLUTD may occur in association with uroliths (stones), with microcalculi (crystals) and or mucous plugs, which also contain crystals. Just as with dogs, struvite (triple phosphate) and calcium oxalate are the most common feline stones. Different from dogs, most struvite stones in the cat are NOT associated with a bladder infection as the urine is sterile. As with dogs, there must be a high concentration of urolith forming constituents in the urine, there must be a favorable pH and there must be time for the crystals to form. 

 Urethral obstruction is more common in the male cat which is due to the length and the narrow diameter of the male urethra. Many obstructions are a combination of mucus plugs that also contain crystals. In addition, there is local inflammation that develops in response to the urethral crystals and plugs and that makes things worse as the diameter of the urethra becomes even more narrowed when it is inflamed. Even catheterization which is designed to relieve an obstructed urethra can contribute to urethral inflammation and edema. 

 A second common urolith in cats is calcium oxalate. These stones/crystals are becoming more common in cats, in part due to urine acidifying diets that are prevalent and designed to prevent struvite related FLUTD which is a true conundrum. Primary bacterial infections causing signs of FLUTD are rare in young cats (as compared with dogs). 


Urinary tract infections do occur in cats, they are more common in older cats, and more often seen in cats whose host defense mechanisms have been altered. Huh? Host defense mechanisms are those things that keep us protected. Complete voiding of the bladder is a host defense mechanism. So that means the things that prevent complete voiding of the bladder can contribute to UTI. Things like partial obstructions, anatomic abnormalities, detrusor (a muscle in the bladder) atony (weakness) all interfere with complete emptying of the bladder. Thus they can contribute to a UTI. Catheterization, especially the placement of an indwelling urinary catheter, can contribute to UTI. Chronic inflammation associated with FLUTD can also contribute to the development of UTI in cats.  

 Now here is an interesting bit of information. There are similarities between cats with idiopathic FLUTD and women with interstitial cystitis. These similarities include chronic irritative voiding patterns, sterile urine, a prominent bladder mucosal vascularity, decreased mucosal production of glycosaminoglycan and increased numbers of mast cells and sensory afferent neurons. The cause of interstitial cystitis in women is also unknown. 

Contributing causes and risk factors

  • Decreased urine volume and decreased frequency of urination. 

What are some of the things that contribute to decreased urinary volume and frequency? Dirty cat boxes.Poorly available litter box. Decreased physical activity as a result of cold weather. Obesity. Illness or confinement. Decreased water consumption due to water taste, availability or temperature. 

Ÿ • Stress 

Increased plasma concentrations of norepinephrine have been documented with cats with idiopathic FLUTD. This leads to increased nociceptive nerve fiber activity and activates neurogenic bladder inflammatory responses. Furthermore, decreased cortisol concentrations have been observed in these cats too. Although the role of stress is difficult to prove, it is often implicated. The history often indicates recent stress, boarding, cat shows, a new pet or new baby in the home or rainy weather. An inordinate amount of FLUTD shows up following rainy weather. 

Signs and Symptoms

Signs depend on the component of disease present, meaning unobstructed vs. obstructed. Unobstructed cats have frequent urination, straining and difficulty urinating, and blood in the urine. These cats will often lick their genitalia and vocalize during voiding. They will also urinate in inappropriate places. For whatever reason, urinating in sinks and bathtubs is common. Cats with either partial or complete obstruction will strain and strain in the cat box and vocalize during voiding. They will hide. Their abdomens are painful. Some will throw themselves on the floor they are so uncomfortable. Sometimes their penis will be extended from prepuce. 

 I feel like this next bit should be prefaced by a warning. What I’m about to describe is not pleasant. The above description fits an obstructed cat early in his obstruction. This is what an obstructed cat looks like in the first 6 to 24 hours. If the obstruction is not relieved, the symptoms become characteristic of post renal azotemia, including anorexia, vomiting, dehydration and depression. Weakness, collapse, stupor, hypothermia, hyperventilation and slow heart rate, then death. This isn’t a maybe. It happens. And it is a tough way to die. I will say it again. You know your cat better than anyone else. You live with your cat every day. If you see or hear something that just isn’t right, bring the cat in to get checked out immediately. Given what I just described, it is always better to be safe than sorry.  

The physical exam and treatment plan

The physical exam will determine whether or not we are dealing with an obstructed cat or a nonobstructed cat. Non obstructed cats will frequently present with a small, thickened bladder. For the initial presentation, a urinalysis is performed. If bacteria are seen in the urinalysis, a culture and sensitivity is performed. A dietary history is also performed to see if the cat needs to be moved to an acidifying diet. For cats with recurrent non-obstructive lower urinary tract signs, radiograph and ultrasound exams will likely be recommended. Signs will be managed with anti-inflammatory drugs (NSAIDs, glucocorticoids) anti-spasmodics (phenoxybenzamine), glycosaminoglycans, narcotic pain relief. Diet changes will also be suggested. Switching from a dry diet to canned diet to help increase water consumption and decrease urine concentration is recommended. Decreasing stress is another beneficial idea. 

The obstructed cat

This guy is different. There is urgency in relieving his obstruction. How this guy is treated depends on the shape he is in when presented. If he is alert and does not yet have blood values indicating the renal failure associated with urinary tract obstruction, he will be sedated, the obstruction will be relieved and a urethral catheter will be placed. However if he is depressed, lethargic, has a slow heart rate and/or is hypothermic, we must address his hyperkalemia (elevated blood potassium) before moving to anesthetize prior to placing urethral catheter. Hyperkalemia develops when the cat cannot urinate and get rid of potassium. The elevated potassium has effects on cardiac conduction. Remember an obstructed cat has a life threatening condition and without prompt treatment these cats can die. Depending on the severity of the signs, he may need to be hospitalized for a few days. The hyperkalemia is addressed in a relatively rapid fashion, followed by relieving the obstruction. Continuous fluids are administered over the next 24 hours as some obstructed cat will undergo something called a post-obstructive diuresis. Fluids and other supportive measures are needed for the next few days. The urinary bladder may have been so stretched from over distension that it needs to be expressed several times a day or an indwelling urinary catheter is left in place while the overstretched bladder muscle regains it’s tone.


If the causative factors to a particular cat’s FLUTD can be identified, then prevention may be possible. For example, the cat with a bacterial UTI can have his UTI treated and resolved. The cat with struvite stones can have them dissolved through diet and the cat with alkaline urine and struvite crystalluria can be treated with a urine acidification diet. For those cats that already have acid urine, a urine acidification diet will not help. However, they can be helped by feeding canned food to encourage water consumption resulting in more dilute urine. Some cats with idiopathic FLUTD can be helped with glucosamine and some with amitriptyline. 

Perineal Urethrostomy

There is a subset of cats, that will continue to obstruct no matter what dietary and medical means have been undertaken to try and prevent their repeated obstruction. For these cats, perineal urethrostomy is an option. This is a surgery, in which the penis is cut “lengthwise” deep towards the urinary bladder. The incision is carried forward until a wide spot in the urethra is reached. The urethra is then sutured to the skin. The advantage is that cats who have successful urethrostomies do not obstruct again. Because we have altered their host defense mechanisms, they are at some risk for bacterial urinary tract infections. I would propose that dealing with a UTI is better than dealing with an obstructed and potentially dead cat. 

 So, there you have it. FLUTD in a nutshell. And now a bit of trivia. As I sat here writing this, I was listening to Adagio for Strings. Do you know which movie soundtrack lays claim to the most infamous use of this piece?


Until next week……


Dr. Voorheis  

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