Veterinary Medicine - October 2008 - (Page 555)

Prevention* • Dog: Feed a diet formulated for managing cystine calculi and thiol disulﬁde exchange drug, or feed a preferred diet and MPG, water, and potassium citrate. • Cat: Feed a diet formulated for managing kidney disease. Avoid diets high in plant protein. Comments Cystine crystalluria is always considered abnormal, but this ﬁnding is not always associated with urolith formation. • Primarily reported in dogs • No relationship between urine pH and urolith formation established • No prevention protocol is available. • Search for and treat inﬂammatory and ischemic causes of hematuria. • Increase ﬂuid intake (e.g. feed canned food). • Have been found in both the upper and lower urinary tract in cats only • Urolith not identiﬁable by ultrasonography uroliths, special dietary management is not speci cally indicated. The key to preventing these uroliths is to eradicate the bacterial infection and periodically monitor for infection recurrence with urinalyses and bacterial cultures.26 Calcium oxalate Calcium oxalate uroliths have had an inverse relationship with struvite uroliths over the last several years in both dogs and cats.21,23 In dogs, as the incidence of struvite uroliths has gradually decreased, the incidence of canine calcium oxalate uroliths has steadily increased, surpassing struvite in frequency of occurrence.21 The incidence of struvite and calcium oxalate uroliths in cats has followed a similar course except for the last few years, which have seen a decline in the incidence of calcium oxalate and an increase in struvite uroliths. In 2005, the Minnesota Urolith Center reported calcium oxalate was the second most frequent type of urolith in cats.22 and dogs.14,23 Small-breed dogs are predisposed, including miniature schnauzers, Lhasa apsos, Yorkshire terriers, bichon frises, Shih Tzus, and miniature poodles.29 Dogs 8 to 12 years old and older cats (bimodal peaks at 5 and 12 years of age) have the greatest risk of developing calcium oxalate uroliths.14,23 Cat breeds predisposed to calcium oxalate formation include Ragdolls, British shorthairs, foreign shorthairs, Himalayans, Havana browns, Scottish folds, Persians, and exotic shorthairs.25 Cats housed indoors may also be at a greater risk for developing calcium oxalate uroliths, which could be a result of a decrease in water consumption and voiding.30 Calcium oxalate uroliths are radiopaque and are usually readily seen on survey radiographs. This urolith type varies in size and shape, taking on a smooth appearance or jagged rose rock appearance. Calcium oxalate uroliths are made up of two different types of crystals, monohydrate and dihydrate. Calcium oxalate uroliths composed predominantly of monohydrate crystals, which appear in the shape of a dumbbell or have a picket-fence shape microscopically, usually have a smoother contour grossly than do uroliths composed predominantly of dihydrate crystals, which have a classic Maltese-cross appearance and are more likely to produce a urolith with an irregular surface. Calcium oxalate crystals precipitate more readily in urine with an acidic pH.31 Hypercalcemia is a predisposing factor for calcium oxalate urolith formation and has been reported in 35% of cats with uroliths and in about 4% of dogs with uroliths.14,30,31 The hypercalcemia observed in this cat population is usually idiopathic, while dogs most often have primary hyperparathyroidism. In dogs, hyperadrenocorticism, which has been associated with hypercalciuria, also increases the risk of developing calcium oxalate uroliths.32 Hypercalciuria contributes to calcium oxalate formation in some dogs and cats as a result of hyperabsorption of calcium from the intestines or renal leak hypercalciuria, which is associated with decreased renal tubular calcium reabsorption.33 When possible, treat these underlying conditions through diet, medication, or surgery to lessen the risk of calcium oxalate urolithiasis. Treatment. Treating calcium oxalate uroliths is limited to surgical removal, voiding urohydropropulsion, and lithotripsy since no method of medical dissolution is available. Leaving the uroliths in place may be a reasonable option in some asymptomatic patients. Continue monitoring the patient for the development of clinical signs and employing measures to prevent further calcium oxalate formation. Prevention. In dogs, recurrence rates of up to 50% within three years of initial diagnosis have been reported,24 so preventing initial urolithiasis is key. Although many con icting factors have been reported regarding the best diet for calcium oxalate urolith prevention, protein and oxalate restriction VETERINARY MEDICINE October 2008 Characteristics. Calcium oxalate urolith formation has been reported to have a male predisposition in both cats 555

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Veterinary Medicine - October 2008 Contents Leading Off Clinical Exposures Idea Exchange Stalking Stones Vaginitis in Dogs CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - October 2008

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