Because the composition of the nephroliths was very unlikely to be struvite, medical dissolution protocols were not considered.
Would you recommend that a nephrolithotomy be performed in this cat? In cats with CRF and nephroliths, the potential benefit
and risk associated with surgical removal of the stones should be carefully evaluated. If the kidney(s) with non-obstructing
nephroliths is likely contributing a significant component of remaining renal function (as was the situation with this cat),
the substantial risk of further decline of renal function associated with nephrotomy may negate the potential benefit of surgery.
In addition, sudden onset of a uremic crisis associated with outflow obstruction caused by movement of the nephroliths into
the ureters was deemed to be unlikely in this cat because the stones were too large to pass into the ureteral lumen(s). Therefore,
a nephrotomy was not recommended. Clinical experience has revealed that increases in the size and number of many metabolic
nephroliths may be minimized with appropriate dietary therapy. Some of the modifications characteristic of canned renal-failure
diets may also minimize some dietary risk factors associated with calcium oxalate uroliths. However, the serum concentration
of calcium should be monitored if renal failure diets with increased levels of vitamin D are fed.
The owners were encouraged to return in approximately two to three weeks for re-evaluation of the status of renal function
and the nephroliths. But because the cat's quality of life as judged by the owners was good, they did not return to the hospital
for re-evaluation at that time.
Recurrence of clinical signs: Day 242
What's your diagnosis?
The cat was evaluated eight months later (day 242) when the owners became concerned because she developed progressive depression
and anorexia over a two- to three-day period. They indicated that during the past two months, the cat was becoming progressively
polydipsic and polyuric. However, there was no evidence of pollakiuria or dysuria. Physical examination revealed that the
cat was slightly dehydrated (estimated to be 6 percent loss of body weight). Temperature (101.5 F), respirations, pulse rate
and systolic blood pressure were normal. The left kidney was smaller than the right kidney; the urinary bladder was normal.
Results of a serum chemistry profile indicated an increase in the severity of azotemia, hyperphosphatemia and acidemia (i.e.
reduction in the serum concentration of total carbon dioxide; Table 1). Results of a hemogram revealed immature neutrophilia
associated with leukocytosis and non-regenerative anemia (Table 1). Survey radiographs of the urinary tract revealed that
the nephroliths were similar in size and number to those evaluated six months previously. Ultrasonography revealed no evidence
of urinary outflow obstruction associated with the nephroliths.
Table 2. Urinalysis and urine culture results
Analysis of a pretreatment sample of urine collected by cystocentesis revealed that the urine specific gravity was inappropriately
low in the context of clinical dehydration. There was evidence of infectious inflammation (pyuria, hematuria, proteinuria
and bacteriuria; Table 2). Crystals were not detected in the urine sediment.
Problems identified included:
1) primary chronic polyuric azotemic renal failure,
2) bilateral nephroliths,
3) secondary bacterial urinary tract infection probably involving the kidneys.
Why did this cat develop bacterial UTI?
Because the urinary tract is inherently resistant to bacterial urinary tract infection, underlying abnormalities in one or
more of this cat's host defenses against UTI were likely. Bacterial UTI can be a cause, or, as was likely in this patient,
a consequence of renal failure.
In a study of cats with renal failure evaluated at the University of Minnesota Veterinary Teaching Hospital, approximately
20 percent had concomitant bacterial infections. Abnormalities associated with renal failure that increase the risk for secondary
bacterial UTIs include decreased urine concentration, altered urine composition and impaired cellular and humoral immune responses.
In addition, the nephroliths predisposed this patient to secondary bacterial UTI.
Can you localize the bacterial UTI?