Page 939 - Small Animal Clinical Nutrition 5th Edition

Feline Lower Urinary Tract Diseases 971

Assess the Food and Feeding Method
The cat was given a variety of commercial dry and moist cat foods before the urocystoliths were removed one year ago. After sur-
VetBooks.ir gery, the food was changed to a commercial dry veterinary therapeutic food formulated to avoid excessive magnesium and phos-
a
phorus and to allow production of normal acidic urine.These nutritional attributes are important for prevention of struvite crystal-
luria. This food was offered free choice.

Questions
1. Why were no crystals identified in urine from this patient?
2. What is the probable composition of the recurrent uroliths in this cat?
3. How should this cat be treated and how can urolith recurrence be minimized?

Answers and Discussion
1. Crystals were not seen in the urine sample because the urine was not supersaturated with crystal-forming substances at the time
the sample was collected and examined. This finding suggests an absence of the typical combination of factors that lead to the
initiation, nucleation, growth and aggregation of crystals. Some factors that influence the variable presence of crystals include
time since the last meal, how concentrated or dilute the urine is, how the urine sample is handled after collection, fluctuations in
urinary pH and differences between the food consumed at home vs. that in the hospital.
2. The urocystoliths are probably composed of calcium oxalate, based on the signalment (calcium oxalate occurs more commonly
in neutered male, middle-aged cats with a higher prevalence in Burmese, Himalayan and Persian breeds) and clinical findings
(i.e., aciduria, radiodense uroliths and analysis of the previous uroliths).
3. Medical protocols to promote dissolution of calcium oxalate uroliths in cats are currently unavailable. Urocystoliths small enough
to pass through the urethra may be removed by voiding urohydropropulsion. Very small urocystoliths may be retrieved with the
aid of a urinary catheter. At present, cystotomy is the only practical alternative for removing larger calcium oxalate uroliths.
Following urolith removal, medical protocols should be considered to minimize urolith recurrence. In general, medical therapy
should be formulated in a stepwise fashion, with the initial goal of reducing urine concentration of lithogenic substances.
A food that provides adequate protein (>32% dry matter), avoids excessive calcium and sodium chloride and does not promote
formation of overly acidic urine (urinary pH <6.2) should be considered to help minimize recurrence of calcium oxalate uroliths
in this cat. Potassium citrate helps promote increased urinary pH and may inhibit formation of calcium oxalate crystalluria; it is
present in some therapeutic urinary foods. b,c The food should not contain restricted or increased levels of phosphorus or mag-
nesium. Excessive intake of vitamin D (which promotes intestinal absorption of calcium) and ascorbic acid (a precursor of oxalate)
should be avoided by not offering vitamin supplements. The food should be adequately fortified with vitamin B (pyridoxine)
6
because pyridoxine deficiency may promote endogenous production and subsequent urinary excretion of oxalic acid. Most com-
mercial foods contain more than adequate levels of pyridoxine; however, homemade foods might be deficient if they are not sup-
plemented.
Other preventive measures include increasing urine volume and maintaining less concentrated urine by feeding moist (canned)
rather than dry food. Drugs (e.g., furosemide, glucocorticoids) that may increase hypercalciuria should be avoided.
Hydrochlorothiazide diuretics may decrease urinary calcium oxalate saturation in healthy cats; however, there currently are no
data to indicate their effectiveness in cats with calcium oxalate uroliths. Serial monitoring (e.g., radiographs, urinalyses, serum
biochemistry profiles) should be performed every six months to detect underlying metabolic problems, and to aid detection of
recurrent uroliths when they are small enough to be removed by nonsurgical techniques.

Progress Notes
Abdominal radiographs were reviewed to ensure that radiodense nephroliths were not overlooked.The urocystoliths were removed
via cystotomy. Because the number of uroliths could not be determined from the pre-surgery radiographs, postsurgical radiographs
were taken to confirm that all of the uroliths had been removed. Evaluating postsurgical radiographs is important because failure
to remove all urocystoliths during surgery is possible and may result in the appearance of recurrence of clinical signs and uroliths
b
despite preventive measures. A moist veterinary therapeutic food that provided the appropriate nutritional benefits discussed above
d
was prescribed; the nutritional benefits of this food currently are available in different food. Because the cat was thin (BCS 2/5),
the daily energy requirement (DER) was estimated to be 1.4 x the resting energy requirement at the ideal weight of 4 kg (DER =
265 kcal [1,109 kJ]). The owners were instructed to divide the amount of food supplying the DER into two daily feedings and
monitor the food intake closely until optimal weight was achieved.
Serial monitoring consisted of periodic urinalyses (with emphasis on urine specific gravity, urinary pH, crystalluria and evidence
of urinary tract infection), survey radiographs and serum biochemistry profiles (serum calcium and electrolytes). Initially, routine
urinalyses were performed every two to four weeks and the owners were carefully interviewed to assess compliance with feeding
recommendations.