Canine and Feline Urolithiasis II

Feline Urate Urolithiasis After CaOx and struvite containing uroliths, urate uroliths appear to be the third most common mineral type submitted to our laboratory from cats. Although fluctuations in the percentage of struvite and CaOx containing uroliths have occurred over the past 25 years, the same does not appear to be true of urate uroliths. Therefore, it appears that whatever changes occurred in the feline diet market, these changes did not appear to influence cats that were predisposed to urate stones. No differences in gender were found in cats with urate urolithiasis (49% female and 51% males). 1 Because it is reported that cats with urate stones may have a portosystemic shunt or other liver dysfunction, we have recently evaluated 159 records of cats that presented to primary care and referral veterinarians for urate urolithiasis. A retrospective analysis of feline urate uroliths submitted to the GV Ling Urinary Stone Analysis Laboratory between 2000 and 2008 was included. 2 From these data, records were assimilated from referring veterinarians (143); furthermore, all recorded cases from within the William R Pritchard Veterinary Medical Teaching Hospital (16) were included. Median values for the complete blood count and chemistry panels available were within the reference intervals, when provided, with only a few outliers present. Of all cases evaluated, seven had a portosystemic shunt (PSS); the majority of cats with PSS were from the VMTH. Cats with urate uroliths and a PSS were younger than cats without a PSS (2years vs. 7years). The pathogenesis of urate uroliths in cats is poorly understood. Most cats were not completely evaluated for a PSS, however, clinicopathologic parameters indicating hepatic dysfunction were seldom noted; more sensitive diagnostics such as serum bile acids were rarely performed to confirm or negate the presence of a shunt. Specific breeds such as the Egyptian Mau and Siamese have been reported to be at increased risk for urate stones. Prospective studies are needed to see if full liver evaluations are warranted in breeds that are predisposed, as well as cats without a history, clinical signs and screening blood work suggestive of a PSS. When evaluating recurrence rates of 221 cats with urate stones, 10.9% had a recurrence of a urolith and 2.9% had a subsequent presentation for urolithiasis. 3