The wacky world of bladder stones – Episode 1
March 20, 2014
From the desk of Dr. Voorheis
Here I sit again preparing for blog Thursday and thinking about what I see consistently in my practice of veterinary medicine. One thing high on that list is definitely bladder stones and urinary tract infections. Many of you are already intimately aware that some dogs and cats develop bladder stones. I’ve walked that path with many clients and critters over the years. This week, I will talk about the why and how of it all and provide some information about how we diagnose and treat this pesky problem.
As usual, let’s start at the beginning to set this up so that everyone can get a handle on the basics. I’ll start by explaining that urine is a complex solution in which salts such as calcium oxalate and magnesium ammonium phosphate can remain in the solution under conditions of “supersaturation“. Super what you say? Ok, think of it this way. Put some salt in water and stir. It dissolves, right? Put enough salt into the water and there will be a point where it can’t dissolve anymore. The water is saturated with sodium and chloride ions. And here begins “supersaturation”.
Many dogs and cats have urine saturated with these complex salts. This saturated urine has the potential to form solids from the dissolved salts. Crystalluria is a consequence of urine supersaturation and uroliths (stones) may form if crystals aggregate (get together) and are not excreted. Stones can damage the uroepithelium and result in urinary tract inflammation. Now we start to see signs including blood in the urine, frequent urination, straining to urinate, difficulty urinating and possibly even excessive licking of the genital area. This will predispose the animal to the development of a bacterial urinary tract infection, especially in dogs. If the stones lodge in the urethra, urine flow may be obstructed. If they form or lodge in ureter, urine flow may be obstructed and kidney damage can and will occur. Fortunately, most stones are found in bladder. Some are found in the urethra while only about 5% are found in the kidneys or ureters.
Just like people, these stones come in all shapes and sizes and are made up of different “stuff”. We classify stones based on what “stuff” they are made of, i.e. their mineral content. About 40% of all canine bladder stones are made up of Calcium oxalate. Another 40% are made of struvite which is magnesium ammonium phosphate. About 5% are urate stones and another tiny 1% are cysteine stones. Another 1% are silicate and the rest are mixed or compounded. The numbers for the first two crystals are similar in cats. Calcium oxalate is slightly more common than struvite stones but they both make up more that 80% of feline bladder stones. Urate stones and dried solidified blood are found in cats more than in dogs. Bladder problems in cats are often lumped into “the feline lower urinary tract diseases”, or FLUTD. That is the subject for an upcoming blog because it is such a large subject and worthy of an entire blog. Besides, my feline clients are going to get a little tired of blogs about dog problems with a little cat thrown in for good measure. Oh believe me; cats have their own set of interesting issues. Coming soon to a blog near you….. FLUTD.
We know that certain conditions make it easier for crystallization of salts to occur and for the formation of bladder stones to happen. For example, having a sufficiently high concentration of salts in the urine and time in the urinary tract to crystallize can contribute to the creation of stones. Having a urine pH favorable for the salts to crystallize (come out of solution) and a center on which crystallization can occur can also contribute to bladder stones forming. A high dietary intake of minerals and proteins coupled with a dog’s ability to produce concentrated urine contributes to “supersaturation” of urine with salts. Some dogs that don’t drink enough water have a greater chance of urolith formation. In certain breeds there is decreased tubular resorption of calcium, cystine and uric acid in the kidneys. Increased production of these salts is secondary to bacterial infection. There are different theories of urolith formation with the primary factor being the supersaturation of urine with salts vs. substances in the urine that promote or inhibit crystal formation. The most common bladder stones are:
• Struvite uroliths – also known as magnesium ammonium phosphate stones. Because most canine diets are rich in minerals and protein, canine urine frequently becomes saturated with magnesium, ammonium and phosphate. However, a UTI (urinary tract infection) is an important factor predisposing to the formation of struvite uroliths in dogs. Staphylococcus and Proteus are the most common bacteria associated with struvite stones. These bacteria contain enzymes which help turn the urine alkaline (by splitting urea) which decreases the solubility of struvite (so the crystals come out of solution easier). Bacterial infections produce organic debris available as a crystallization surface. These stones are more commonly associated with female dogs. Interestingly, cats form struvite stones without concurrent bladder infections but cats produce far more concentrated urine than dogs do. Most common breeds affected: Miniature Schnauzers, Miniature Poodles, Bichon Frises, Cocker Spaniels
•Calcium Oxalate Uroliths- The causes of formation of calcium oxalate stones are poorly understood. Hypercalciuria (high concentrations of calcium in the urine) is certainly a factor. In some dogs this occurs after eating. Others don’t reabsorb calcium in their kidneys resulting in excess urine calcium production. Treatment of some dogs with furosemide which is a diuretic can lead to formation of these types of stones. Treating other dogs with corticosteroids where there is naturally occurring increased corticosteroid production can lead to formation of these types of stones as well. Increased dietary intake of certain vegetables high in oxalates, grass, and vitamin C may play a role in development of calcium oxalate urolithiasis. There has been an increase in these types of stones over the past 15 years or so corresponding to the increased use of urine acidifying diets. These crystals come out of solution in an acid pH urine. About 70% of the calcium oxalate uroliths are found in male dogs. Most common breeds affected: Miniature and Standard Schnauzers, Miniature Poodles, Yorkshire Terriers, Lhasa Apsos, Bichon Frises, Shih Tzus.
•Urate uroliths -These stones are composed of ammonium acid urate. It is hypothesized that the hepatic transport of uric acid is defective in Dalmatians and some English Bulldogs because uric acid conversion to allantoin has been found to be decreased in them. In addition to decreased hepatic metabolism, in some Dalmatians the kidney does not reabsorb uric acid. End result is that the Dalmatian excretes about 10 times the urates that other dogs do, although urate stones form in only a small percentage of them. Male Dalmatians form urate stones at a much higher rate than females (like 16 to 1). Other at risk breeds include the English Bulldog. Any dog that has hepatic insufficiency (esp due to hepatic cirrhosis, portosystemic shunts) is at risk for developing urate stones (although for these dogs bladder stones are the least of their problems).
•Silicate Uroliths – remember playing with jacks as a kid? Silicate stones are shaped like jacks. It is thought that silicate uroliths form due to dietary intake of silicates, such as eating large amounts of corn gluten or soybean hulls. Remember in blog 2 on nutrition where I wondered when corn became bad? Well, this is a place that is could be a problem. Commonly affected breeds: German Shepherd Dogs, Old English Sheepdogs, Golden and Labrador Retrievers. Older dogs, 6 to 8 years of age.
•Cystine uroliths – cystinuria is an inherited disorder of renal transport and is the primary cause of cystine uroliths. More accurately stated it is a predisposing factor. Not every dog with cystinuria develops cystine uroliths. Dachshunds are the breed principally affected but it is also seen with Basset Hounds, Tibetan Spaniels, English Bulldogs, Yorkshire Terriers, Irish Terriers, Chihuahuas, Mastiffs, and Rottweilers.
Signs, Symptoms and Diagnosis
The signs depend on the number, type and location of the stones within the urinary tract. Most often, the stones are in the bladder so the symptoms are those consistent with cystitis. Symptoms include blood in the urine, frequent urination, straining to urinate, difficulty urinating and excessive licking of the genitals.
In male dogs, smaller stones may pass into the urethra causing partial or complete obstruction. This takes a mild to moderate problem and catapults it into a life threatening emergency. Urethral obstruction can be just as fatal to a dog as it is to a cat. Renal uroliths (kidney stones) are uncommon and can range from being asymptomatic to causing hematurina, chronic kidney infection and pyelonephritis. Ureteral uroliths can be asymptomatic or they can cause hydroureter. The condition is diagnosed from a combination of history, physical exam, radiographs and ultrasound. Sometimes radiographic contrast studies are done to find the stones. Finally, ultrasound examination confirms the findings.
The general principle is prompt relief of any urethral obstruction. This can usually be accomplished by passing a smaller than normal urethral catheter and drawing urine out of the obstructed bladder. This process is called cystocentisis. Another method used is retrograde hydropulsion which is where a stone is forced back into bladder. Only rarely do we have to perform an emergency urethrotomy. With any treatment option, fluid support is key. After the initial wave of support, a decision must be made between surgical removal of the stones and medical dissolution of the stones. Next week I will discuss the treatment of each type of stone in detail but I can provide a bit of information now so that I don‘t leave anyone grasping for answers.
Bladder stones can potentially be eliminated by the dog without any intervention. However, if the stones are not eliminated in a few weeks they may cause damage to the bladder tissues or urinary tract. At that point, the bladder stones should be removed through surgery which is known as cytology.
In many cases the stones can be dissolved over a period of several weeks to several months by feeding the dog a specially formulated diet. Some of the diets I recommend are Hill’s Prescription Diet s/d, Royal Canin Urinary SO 13 or Hill’s u/d. This depends on which type of stone we are dealing with. There is also a drug called haloperidol that is often used. In some cases, feeding a diet such as Canin Vegetarian Formula may help prevent urate stones. There are no methods currently available for dissolving calcium oxalate and silica stones. However, diets and supplements can be used to reduce the risk of recurrence.
Surgical removal makes the most sense for urethral stones that cause obstruction and for bladder stones that fail to respond to a diet change and medication.
To end this week’s blog, I will say again that taking your dog to the vet for regular checkups is your best defense against big medical issues and huge vet bills. Stones that are caught early are much easier to deal with than those left to fester into larger problems. Your dog or cat will thank you for catching it early as it causes them much less pain and discomfort.
Next week…..bladder stones and UTI in cats…it’s a whole wide world of drama!
Until next week……..