Diagnosis, medical treatment, and prognosis of feline urolithiasis

Increased dietary long-chain polyunsaturated fatty acids alter serum fatty acid concentrations and lower risk of urine stone formation in cats

The lifespan of cats with non-obstructive kidney stones is shortened compared with healthy cats indicating a need to reduce stone formation and minimize chronic kidney disease. The purpose of this study was to investigate the effects of increasing dietary polyunsaturated fatty acids (PUFA) on urine characteristics. Domestic-short-hair cats (n = 12; mean age 5.6 years) were randomized into two groups and fed one of two dry-cat foods in a cross-over study design. For one week before study initiation, all cats consumed control food that contained 0.07% arachidonic acid (AA), but no eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA). Group 1 continued eating control food for 56 days. Group 2 was fed test food for 56 days, which was control food plus fish oil and high-AA oil. Test food contained 0.17% AA, 0.09% EPA and 0.18% DHA. After 56 days, cats were fed the opposite food for another 56 days. At baseline and after each feeding period, serum was analyzed for fatty acid concentrations, and urine for specific gravity, calcium concentration, relative-super-saturation for struvite crystals, and a calcium-oxalate-titrimetric test was performed. After consuming test food, cats had increased (all P<0.001) serum concentrations of EPA (173%), DHA (61%), and AA (35%); decreased urine specific gravity (P = 0.02); decreased urine calcium concentration (P = 0.06); decreased relative-super-saturation for struvite crystals (P = 0.03); and increased resistance to oxalate crystal formation (P = 0.06) compared with cats consuming control food. Oxalate crystal formation was correlated with serum calcium concentration (r = 0.41; P<0.01). These data show benefits for reducing urine stone formation in cats by increasing dietary PUFA.

Risk factors for urate uroliths in cats

OBJECTIVE

To identify demographic factors associated with urate urolithiasis in cats and determine whether the rate of urolith submission to a laboratory had changed over time.

DESIGN

Case series and case-control study.

ANIMALS

Cases consisted of 5,072 cats with urate uroliths submitted to the Minnesota Urolith Center between January 1, 1981, and December 31, 2008. Controls consisted of 437,228 cats without urinary tract diseases identified in records of the Veterinary Medical Database during the same period.

PROCEDURES

Information on cat breed, age, sex, reproductive status, and location of uroliths was used to identify risk factors. Changes in annual urolith submission rates were evaluated.

RESULTS

Purebred cats had significantly higher odds of developing urate uroliths than did cats of mixed breeding (reference group). On the other hand, cats of the Abyssinian, American Shorthair, Himalayan, Manx, and Persian breeds had significantly lower odds of developing urate uroliths than did mixed breeds. Neutered cats were 12 times as likely to develop urate uroliths as were sexually intact cats. Cats in all age groups had significantly increased odds of developing urate uroliths, compared with cats < 1 year of age (reference group). Cats ≥ 4 but < 7 years of age had the highest odds of all groups and were 51 times as likely to develop urate uroliths as were cats < 1 year of age. Urolith submission rates did not change significantly with time.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings of this study suggested that the typical cat with urate uroliths was a purebred neutered cat, 4 to 7 years old, with uroliths in the bladder or urethra. This information may be helpful in predicting mineral composition of uroliths in vivo. However, no conclusions can be made regarding cause-and-effect relationships.

Trends in the Frequency of Calcium Oxalate Uroliths in the Upper Urinary Tract of Cats

Medical records from cats diagnosed with uroliths at nine United States veterinary teaching hospitals from 1980 to 1999, and records of cats with uroliths submitted for analyses to the Minnesota Urolith Center from 1981 to 2000, were evaluated. A 10-fold increase in frequency of upper tract uroliths occurred in cats during the 20-year interval at the nine veterinary teaching hospitals. Calcium oxalate emerged as the predominant mineral type in upper tract uroliths, having increased more than 50-fold during the study period. These results emphasize the need for increased awareness of the occurrence of upper urinary tract uroliths in cats.

A model of suture-induced urolithiasis with urographic control in the bladder of the rat

The characteristics of a model of urolithiasis in the bladder of male Wistar rats were evaluated. Two techniques were compared: one knot of suture material through the bladder wall, or 15-throw knots inside the bladder. Rats were randomly assigned to one of six groups, according to the technique and suture material used (polyester, silk, or chromic catgut). An excretory urogram was performed at days 30, 60, and 90. At the moment of positive radiographic diagnosis, animals were sacrificed and stones were obtained. All rats were sacrificed at day 90 regardless of the x-ray results. Variables evaluated were average days to a positive urogram, average weight of all uroliths, and percentage of animals developing urolithiasis throughout the study. There were no statistical differences between groups for the average weight of stones, which ranged from 0.008 to 1.502 g for individual cases. All three materials were more lithogenic with the 15-throw knot inside technique. No significant differences were detected for lithogenesis criteria between suture materials. X-ray dispersion spectroscopy evidenced calcium phosphate composition of two stones from chromic catgut, and magnesium phosphate composition of two stones from chromic catgut, two from silk, and two from polyester. Neo-epithelization over the suture was confirmed microscopically in bladders with the one-throw technique. We conclude that (1) this is an effective model of urolithiasis, with predictability in time, composition, and amount of stone formation; (2) the presence of more suture material inside the bladder is more lithogenic; and (3) excretory urograms are highly sensitive and specific for the noninvasive diagnosis of bladder urolithiasis.