Calcium oxalate urolithiasis in cats

A case of renal oxalosis in a 3-month-old cat raised under controlled conditions

The kidneys of a 3-month-old female cat were examined. The cat which had been raised under controlled conditions with no history of any poisoning showed progressive weight loss with increases in blood BUN and creatinine concentrations. At necropsy, both kidneys were firm in consistency with formation of focal scars. Histopathologically, widespread deposition of crystals was observed in the renal tubules (in both dilated lumina and degenerative epithelia) accompanying mild interstitial fibrosis with lymphocyte infiltration. The crystals were colorless or basophilic on the hematoxilin and eosin-stained section and could be visualized with polarized light as doubly fractile crystals. The crystals were identified as calcium oxalate crystals by histochemical examinations using von Kossa stain and alizarin red S stain under different conditions and by ultrastructural examination. Judging from the above-mentioned findings, the present renal lesion detected in an infant cat was diagnosed as renal oxalosis which was suspected to be hereditary in nature.

Influence of nutrition on feline calcium oxalate urolithiasis with emphasis on endogenous oxalate synthesis

The prevalence of calcium oxalate (CaOx) uroliths detected in cats with lower urinary tract disease has shown a sharp increase over the last decades with a concomitant reciprocal decrease in the occurrence of struvite (magnesium ammonium phosphate) uroliths. CaOx stone-preventative diets are available nowadays, but seem to be marginally effective, as CaOx urolith recurrence occurs in patients fed these diets. In order to improve the preventative measures against CaOx urolithiasis, it is important to understand its aetiopathogenesis. The main research focus in CaOx formation in cats has been on the role of Ca, whereas little research effort has been directed towards the role and origin of urinary oxalates. As in man, the exogenous origin of urinary oxalates in cats is thought to be of minor importance, although the precise contribution of dietary oxalates remains unclear. The generally accepted dietary risk factors for CaOx urolithiasis in cats are discussed and a model for the biosynthetic pathways of oxalate in feline liver is provided. Alanine:glyoxylate aminotransferase 1 (AGT1) in endogenous oxalate metabolism is a liver-specific enzyme targeted in the mitochondria in cats, and allows for efficient conversion of glyoxylate to glycine when fed a carnivorous diet. The low peroxisomal activity of AGT1 in cat liver is compatible with the view that felids utilised a low-carbohydrate diet throughout evolution. Future research should focus on understanding de novo biosynthesis of oxalate in cats and their adaptation(s) in oxalate metabolism, and on dietary oxalate intake and absorption by cats.

Effects of Diet on Urine Composition of Cats With Calcium Oxalate Urolithiasis

Ten client-owned cats with calcium oxalate (CaOx) urolithiasis were evaluated to determine the effect of diet on urine CaOx saturation. Two dietary treatments were evaluated in each cat: the diet consumed just prior to urolith detection and a canned diet formulated to prevent CaOx uroliths. This study revealed that hypercalciuria is a consistent abnormality in cats with CaOx urolith formation. When urolith-forming cats consumed a diet formulated to prevent urolith formation, activity product ratios for CaOx (which estimate the degree to which urine is saturated with CaOx) were significantly lower. These results suggest that consumption of an appropriately formulated urolith-prevention diet will reduce recurrence of CaOx urolithiasis.

Evaluation of trends in frequency of urethrostomy for treatment of urethral obstruction in cats

OBJECTIVE

To determine hospital proportional morbidity rates (HPMR) for urethral obstructions, urethral plugs or urethroliths, and urethrostomies in cats in veterinary teaching hospitals (VTH) in Canada and the United States between 1980 and 1999.

DESIGN

Epidemiologic study.

ANIMALS

305,672 cats evaluated at VTH.

PROCEDURES

Yearly HPMR were determined for cats with urethral obstructions, urethral plugs or urethroliths, or urethrostomies from data compiled by the Purdue Veterinary Medical Database. The test for a linear trend in proportions was used.

RESULTS

Urethral obstructions were reported in 4,683 cats. Yearly HPMR for urethral obstructions declined from 19 cases/1,000 feline evaluations in 1980 to 7 cases/1,000 feline evaluations in 1999. Urethral plugs or urethroliths affected 1,460 cats. Yearly HPMR for urethral plugs or urethroliths decreased from 10 cases/1,000 feline evaluations in 1980 to 2 cases/1,000 feline evaluations in 1999. A total of 2,359 urethrostomies were performed. Yearly HPMR for urethrostomies decreased from 13 cases/1,000 feline evaluations in 1980 to 4 cases/1,000 feline evaluations in 1999.

CONCLUSIONS AND CLINICAL RELEVANCE

Frequency of feline urethrostomies performed at VTH in Canada and the United States declined during the past 20 years and paralleled a similar decline in frequency of urethral obstructions and urethral plugs or urethroliths. These trends coincide with widespread use of diets to minimize struvite crystalluria in cats, which is important because struvite has consistently been the predominant mineral in feline urethral plugs during this period.