VET CHECK: BLADDER INFECTIONS (CYSTITIS)

Featured in the Sept/Oct 2007 Issue of Mushing Magazine:This is a topic that I want to address because it is relatively common and is easily missed in the environment of a typical sled dog kennel. If the early signs are missed, the disease can progress from an issue easily resolved with medical therapy to one that requires surgery, or in some cases a surgical emergency.The environment of the urinary bladder is a perfect culture medium for many bacteria: warm, dark, and with proper nutrients to sustain rapid bacterial growth. In a normal dog, these infections typically begin when bacteria ascend the urethra (the tube the drains the bladder to the outside world). Dogs have several mechanisms to prevent this from happening: the primary tool is simply the force generated by urine flowing down the urethra when the dog urinates, which physically flushes bacteria to the outside world. In addition, the lining of the bladder has a coating of mucus-like material that helps prevent bacteria from adhering to the bladder wall. The tissue of the bladder is also one that heals extremely rapidly after any insult, infection or otherwise.Dogs that are suffering from cystitis will often show increased frequency of urination, straining to urinate, discolored urine (red, orange, green), foul odor to the urine, or frequent licking of the vulva in females or sheath in males. Less common signs are poor appetite, vomiting, and abdominal pain; these can often signal that that the infection has involved more than the bladder (such as kidney infections or obstruction of the urethra). In a house dog, the common signs are usually easy to detect; if you are the one letting the dog outside every time she needs to urinate, you are quickly going to realize that she’s asking to go out much more than normal. In a sled dog that lives outside and urinates whenever she feels like it, you are less apt to pick up on the changes. This is why taking some time every day to simply observe the kennel is so important; most of us are busy feeding, scooping, supervising loose dogs, and so on, that it’s easy to fail to recognize changes from the norm. Snow on the ground will definitely give you a rapid heads-up to discolored urine, and you should be in the habit of checking out yellow snow on a daily basis to be sure all of your dogs are properly hydrated in cold weather anyway!The diagnostic workup when a bladder infection is suspected starts first with a physical exam: the bladder must be palpated for pain or possible bladder stone formation. The vulva in females and the prepuce and prostate in males must be palpated for signs of infection as well. A fresh urine sample must be obtained for examination; this can be done by simply catching the sample in a “cup on stick” when the patient urinates, or it may be obtained directly from the bladder via needle puncture (cystocentesis). Urine obtained by the free-catch method may be affected by any disease process that exists further down the urinary tract (a common example would be a prostate infection in a male dog. Examining the size and shape of the prostate will help the veterinarian differentiate a bladder infection from a prostate infection). A urine dipstick is used to detect the pH, and also for evidence of blood, protein, ketones, glucose, and bilirubin. Normal dog urine will usually have protein in small amounts, and a small amount of bilirubin is occasionally found in normal dogs. Blood is abnormal unless the patient is a female in season. Glucose and ketones are a flag for diabetes mellitus. Urine pH in healthy dogs is usually 6.5 to 7; dogs with infections will often be higher. The urine specific gravity is measured with tool called a refractometer; the reading is used to assess the kidney’s ability to concentrate and dilute the urine. A specific gravity that is equal to that of the blood plasma (between 1.007 and 1.012) can indicate kidney involvement. Any sediment in the urine (for example, blood or crystals) can skew the specific gravity and affect the interpretation of this number. The sediment in the urine is evaluated by spinning a urine sample at high speed in centrifuge, which causes the particles of sediment to sink to the bottom of the sample. This sediment is then examined under a microscope: red blood cells, white blood cells, crystals, epithelial cells, and sperm all may or may not be found. Finally, the urine may be cultured to determine what type of bacteria are present and what antibiotic is most appropriate. Pseudomonas or proteus infections are notoriously resistant to many antibiotics and may require long-term treatment with an appropriate dose of a fluoroquinoline class antibiotic. Your veterinarian will determine if radiographs (x-rays) are necessary; any suspicion of bladder stones, a chronic (long term) infection, or recurrent infection would warrant x-rays.Caught early, most bladder infections resolve with antibiotic therapy alone. The urine should be rechecked at the end of antibiotic therapy to be sure that the test results have normalized. Problems arise when infections are missed for long periods of time, or if there are underlying issues that contribute to prolonged or recurrent infections. The presence of bacteria and an abnormally high pH will often cause crystals to form in the bladder; these are usually struvite crystals (also called triple phosphate crystals). As more crystals form, they begin to clump together and form stones (uroliths). Uroliths range in size from sand-like grit to stones the size of a tangerine. Often, the uroliths can be detected on a physical exam because they can be palpated in the bladder (the bladder is best palpated after being emptied, since a large pool of urine can make them hard to feel). In some unfortunate patients, some of these stones may be passed out of the bladder when the patient urinates, and become lodged in the urethra. The result is complete or partial obstruction of urine outflow, an increasingly painful dog that struggles to pass urine, and an emergency trip to the veterinary clinic to relieve the obstruction. The obstruction and the presence of the stones is usually confirmed with a radiograph (x-ray), and the obstruction is relieved either by flushing the stone back into the bladder, or if this is not possible, by surgically removing the offending stone(s) from the urethra by performing a urethrostomy. Males are much more prone to urinary tract obstruction because the shape of their urethra is narrower than that of a female. Uroliths in the bladder are usually removed surgically. It is possible to dissolve smaller struvite uroliths by feeding a special prescription diet that lowers the pH enough to cause them to dissolve, but this takes months and the dog will be at risk for passing the stones into the urethra at any time. Please also be aware that some other types of bladder stones, such as calcium oxalate stones, will not dissolve at all and must be removed surgically.There is some disagreement among veterinarians about the cause and effect relationship of uroliths to bladder infections; some patients have a tendency to form struvite crystals and stones even when all other tests indicate that infection is absent, and for many years, these patients were managed with prescription diets and in some cases, drugs that are designed to acidify the urine. There is another viewpoint that believes that struvite stones result from infection, period, and that diet changes are not as important as appropriate long term antibiotic treatment and relieving any underlying causes of recurrent infection. Some of these underlying causes include urinary incontinence (abnormal leakage of urine through the bladder sphincter), anatomic defects of the bladder, prostate infections, tumors of the bladder, and skin infections around the vulva in females (obese female dogs will often have fat folds that surround the vulva, trapping urine residue and leading to infection). Older dogs, who suffer from urinary incontinence, that have normal anatomy can often be managed with medical therapy using drugs such as phenylpropanolamine, or in females, diethylstilbesterol. Siberian Huskies are also at higher risk for an inherited defect called an ectopic ureter, in which the ureter, a tube that connects the kidney to the bladder, is abnormally attached outside the bladder into the urethra. Instead of pooling the urine properly into the bladder (where it is safely stored behind the bladder sphincter until the dog urinates), it instead drips urine directly into the urethra, resulting in incontinence and then infection. In some unlucky patients, both ureters are affected. Dogs with ectopic ureters will leak urine constantly, and as puppies will often have urine soaked around the prepuce or vulva. Bladder defects, tumors, and some prostate problems may necessitate x-rays for detection: often contrast radiographs are needed to visualize the problem. To do this, the patient has a contrast material placed into the bladder with a urethral catheter while the patient is sedated to “back light” defects in the lining of the bladder or the presence of stones that are not opaque on an x-ray. If this radiograph is normal, a small amount of air is injected into the catheter, which helps to distend the bladder and backlight any lumps or divots that should not be present. Diagnosis of an ectopic ureter requires a procedure called an intravenous pyelogram, in which a contrast medium is injected directly into a vein. It then goes to the kidney, which filters it out of the blood and into the urine. The contrast’s path down the ureter into the bladder can then be captured on an x-ray to see if the ureter is properly connected to the bladder, or if one or both of them are ectopic. Ectopic ureters can be repaired surgically, but this is a very tricky operation that is typically referred to a surgical specialist.Dawn Brown D.M.V. graduated from the New York State College of Veterinary Medicine at Cornell University and practices small animal medicine and surgery at Carthage, New York. She has been racing since 1982, currently 6 and 8-dog limited class speed racing in the lower 48, Canada and Alaska.

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