VETgirl December 2024 BEAT e-Magazine

QUARTERLY BEAT / DECEMBER 2024

the mechanisms for struvite formation in this species are not well understood and likely involves many factors including genetics, sex, environment, diet and hydration. Unfortunately, the pathophysiology of CaOx uroliths in cats and dogs is also not well understood. There are breed predispositions such as the Miniature Schnauzers, Shih Tzu and Bichon Frise 3,5 and Burmese and Persian cats,4 which suggests a genetic basis for mineral formation. Several other factors can increase the risk for CaOx urolithiasis. For example, any comorbidity that contributes to hypercalcemia such as primary hyperparathyroidism can increase serum calcium concentration and result in excess calcium excretion in the urine. However, oftentimes, the reason for the hypercalciuria remains idiopathic 5 and research, including the mechanisms for hypercalciuria, the role of lipids 6,7 and increased body condition score 8 are ongoing. Surgery (e.g., cystotomy) or other minimally invasive procedures (e.g., laser lithotripsy) 9 are usually necessary for CaOx removal and it is a best practice to confirm complete removal by post-procedure radiography. While CaOx uroliths can’t be dissolved by diet, diet should be part of the prevention strategy; medications, such as thiazide diuretics or potassium citrate, might also be needed in select cases. NUTRITION PLAYS A VITAL ROLE Diet plays a crucial role in preventing future stone formation in dogs and cats. In fact, therapeutic diets also can dissolve struvite stones in dogs and cats, 10,11 thereby avoiding unnecessary surgery. When struvite uroliths are suspected in dogs and cats, diets formulated for struvite dissolution are recommended. Due to their differences in pathophysiology, antimicrobials should be administered to dogs (e.g., amoxicillin) but are rarely indicated in cats. The pet should be rechecked in approximately two weeks (cats) or four weeks (dogs) for radiographic evidence of urolith dissolution. If no evidence of dissolution is noted on digital radiography, the stones should be removed by one of the previously mentioned methods. Dissolution can take several months, especially in dogs. Therefore, if uroliths are decreasing in size, dietary therapy should be continued. Fortunately, clinical signs are usually well controlled during this treatment regimen, but analgesics can be provided if warranted. Struvite prevention diets are rarely necessary in dogs, but dietary therapy should be continued for most cats. Therapeutic diets can also be prescribed to reduce the risk of CaOx formation, but “off- label” diets should be considered in pets with comorbidities. Hydration is extremely important for urolith prevention. This can be accomplished by feeding canned food to the pet or adding water to dry kibble or providing additional hydration supplements. Suggested guidelines recommend specific urine dilution levels to reduce the risk of uroliths – consistently less than 1.030 in cats and 1.020 in dogs. 9 Increasing water intake will increase voiding and dilute mineral precursors.

DIFFERENCES BETWEEN CRYSTALLURIA AND UROLITHIASIS Understanding the differences between uroliths and crystalluria is crucial to guide appropriate diagnostics and treatment. Crystalluria refers to the presence of crystals in the urine sediment examination. Struvite, CaOx and amorphous crystals can not only be identified in the urine sediment due to analytical error but also in some healthy animals without any overt lower urinary tract signs (LUTS). Increased storage time and decreased temperature can lead to in vitro struvite and CaOx crystal formation. 1 Therefore, if the clinician is evaluating urine sediment from a pet with LUTS or from a urolithiasis patient, it is crucial to examine the urine appropriately. The urinary sediment should be evaluated within 60 minutes of collection with the specimen at room temperature. Urate and cystine crystals should not spontaneously precipitate and finding these crystals on a urine sediment exam might warrant further diagnostics depending on the pet’s signalment and history. In properly analyzed urine specimens, crystalluria does not always indicate urinary disease. There is no evidence that crystalluria causes any harm to urinary epithelium and healthy dogs and cats can develop crystalluria due to various factors. Moreover, in animals with urolithiasis, crystalluria noted on urine sediment does not accurately correlate with the mineral analysis of the stone. 2 Dietary intervention for pets with only crystalluria is not usually warranted. Urolithiasis involves actual stone formation within the urinary tract, which often leads to LUTS mentioned above. Cystic calculi are a common occurrence in cats and dogs and the two most common uroliths in both species are CaOx and struvite uroliths. 3,4 The pathophysiology for these uroliths is likely multifactorial and are discussed separately below.

FEATURED STORY

In this VETgirl feature article sponsored* by the Purina Pro Plan Veterinary Diets, Dr. Jodi Westropp, DVM, PhD, DACVIM (Internal Medicine) reviews what you need to know about the diagnostic workup and treatment plan for dogs and cats with cystolithiasis. After all, we see and diagnose this all the time, but what do we do for long-term management? * Please note the opinions of this blog are the expressed opinion of the author and not directly endorsed by VETgirl.

UNDERSTANDING DIAGNOSTICS AND TREATMENT FOR DOGS AND CATS WITH CYSTOLITHIASIS DIET PLAYS A VITAL ROLE IN THE ONGOING TREATMENT AND PREVENTION

BY DR. JODI L. WESTROPP PhD, DACVIM University of CA, Davis

Urolithiasis is a common urinary tract disease encountered in dogs and cats. Uroliths are most often diagnosed on plain radiography, ultrasonography or a combination of the two. As veterinarians, we often see patients present with previous history, concerns or clinical signs of lower urinary tract discomfort, such as stranguria, pollakiuria, hematuria or a combination of these signs. Moreover, urolithiasis can be life- threatening and lead to complete urethral or ureteral obstruction in cats and dogs. It is important to understand the underlying pathophysiology for urolith formation as well as diagnostic approaches for evaluating dogs and cats with suspected urolithiasis. This will allow us to formulate better treatment and prevention strategies, including dietary solutions for the most common uroliths in dogs and cats. In this overview, we will focus primarily on the two most common uroliths noted in these species, struvite and calcium oxalate (CaOx).

STRUVITE UROLITHIASIS: BIG DIFFERENCES BETWEEN CATS AND DOGS

In dogs, unlike cats, struvite uroliths typically form due to infections with a urease-producing bacteria, altering urine chemistry and raising urinary pH levels. Struvite urolithiasis in cats usually form in the absence of urinary tract infections. An elevated pH provides the right environment for minerals like magnesium, ammonium and phosphate to precipitate and form struvite stones. The most common urinary pathogen that contributes to struvite urolithiasis in dogs is Staphylococcus spp. Therefore, in dogs with urinary tract calculi, a urine culture is warranted; if Staphylococcus spp. is isolated on aerobic urine culture, the urolith is likely comprised, at least in part, of struvite. Unlike dogs, struvite urolithiasis in cats is usually sterile and

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