Nephroliths and bacterial UTI in a cat with chronic renal failure

How would you manage this patient?
Mar 01, 2006

Anorexia and weight loss in a cat: Day 1

What is your diagnosis?

A 7-year-old female spayed domestic short-hair cat was evaluated at the University of Minnesota Veterinary Medical Center because of partial anorexia and weight loss of several weeks' duration. The cat had been recently adopted from owners who were informed that they were in violation of policies related to housing of animals. The new owners wanted an opinion as to the likelihood that the anorexia and weight loss were related to a change in living environment. According to them, the cat consumed plenty of water. They were unsure about urine volume; however, there was no evidence of pollakiuria or dysuria.

Table 1. Hematology and serum biochemical values
Physical examination revealed that the cat was mildly dehydrated (estimated to be 5 percent loss of body weight). Temperature (101 F), respirations, pulse rate and systolic blood pressure were normal. Abdominal palpation revealed that the left kidney was somewhat reduced in size; the urinary bladder was normal.

Results of a serum chemistry profile revealed that the concentrations of creatinine and SUN were abnormal (Table 1). Serum concentrations of phosphorus and calcium were normal. Results of a hemogram revealed values within the normal reference range (Table 1). Analysis of a urine sample collected by cystocentesis prior to any form of therapy revealed that the specific gravity was inappropriately low in the context of clinical dehydration. The urine was acid and contained evidence of hematuria (Table 2).

Crystals were not detected in the urine sediment. Aerobic culture of an aliquot of urine collected by cystocentesis did not result in growth of bacteria. Survey radiographs of the urinary tract revealed bilateral radiodense nephroliths; there was no evidence of uroliths in the lower urinary tract. Ultrasonography revealed no evidence of urinary outflow obstruction associated with the nephroliths. The left kidney was reduced in size. A diagnosis of chronic azotemic polyuric renal failure associated with nephroliths was made. The owners were advised of the likelihood of a favorable short-term prognosis for response to treatment of the clinical manifestations of chronic renal failure.

What clinical signs are commonly associated with early renal failure in cats?

The frequency of occurrence of renal failure in cats substantially increases when they reach 7 to 8 years of age. However, early detection of chronic renal failure (CRF) is often difficult in cats because early premonitory signs [anorexia (80 percent), weight loss (72 percent), dehydration (70 percent), depression (68 percent), poor nutritional status (58 percent), and weakness (47 percent)] are nonlocalizing and therefore do not direct the clinician's attention to the urinary tract. Signs indicative of renal involvement, such as polyuria and polydipsia (40 percent) and abnormal kidney size (25 percent) occur less frequently. Therefore, appropriate tests of renal function, initially including urinalysis and serum creatinine concentration, should be routinely performed in older cats with the aforementioned non-localizing clinical signs.

Are upper tract uroliths commonly associated with renal failure?

In cats, approximately 65 percent of the upper-tract uroliths are composed of calcium oxalate, while less than 5 percent are composed of struvite. During recent years, calcium oxalate nephroliths have been encountered with sufficient frequency in cats with CRF to warrant radiography or ultrasonography as a standard component of evaluation. The etiologic interrelationship of CRF and calcium oxalate nephroliths is not known, but risks for both disorders may be linked, at least in part, to hypercalciuria and acidosis.

How would you treat this patient?

Our initial therapeutic plans consisted of correcting the dehydration with lactated Ringer's solution given subcutaneously. Supportive management of the renal failure consisted of recommendations to feed a canned non-acidifying renal-failure diet with reduced quantities of phosphorus, sodium and high-quality protein, and adequate non-protein calories to minimize catabolism of protein for energy.

How would you manage the nephroliths?