Advances in feline nephrology

IN SMALL ANIMAL MEDICINE AND SURGERY

VOLUME 20, ISSUE 10 • OCTOBER 2007

Advances in Feline Nephrology MARK J. ACIERNO, MBA, DVM, DACVIM ASSISTANT PROFESSOR LOUISIANA STATE UNIVERSITY SCHOOL OF VETERINARY MEDICINE BATON ROUGE, LA 70803 Recent advances in feline nephrology include dietary modification to treat chronic renal disease and assessment of the risk of urinary tract infections with hyperthyroidism, diabetes mellitus, and chronic kidney disease. DIETARY MODIFICATION TREATMENT OF SPONTANEOUS CHRONIC RENAL DISEASE Chronic kidney disease (CKD) is a common ailment which affects older cats. Some have estimated that 15% of cats 15 years or older are azotemic. Progressive structural lesions causing impairment of waste excretion, hormone production, and electrolyte and acid base balance regulation characterize the disease process. Although progressive in nature, the clinical course is highly variable with many patients experiencing periods of stable renal function. Four stages of CKD are recognized (Table 1). The ability of dietary modification to slow the progression of CKD has been

demonstrated with experimentally induced models of renal failure. Only one study examined the effect of diet in clinical cases which concluded that dietary modification was beneficial. Unfortunately, the study was neither randomized nor blinded. A recent study1 was performed to determine whether cats with stage 2 or 3 CKD (serum creatinine 2.1 to 4.5) would experience fewer uremic crises, slower progression of disease, and lower mortality if fed a diet for treatment of renal failure. Fortyfive client-owned cats with stable renal disease were randomly assigned to receive either a maintenance diet (23 cats) or a renal failure treatment diet (22 cats). Each cat was evaluated after 4 weeks and then every 3 months for 24 months. Evaluations included a medical history, physical examination, funduscopic examination, body condition score, serum biochemical panel, serum parathyroid hormone concentration, hemogram, venous blood gas, urinalysis, urine culture, and blood pressure measurement. Telephone interviews with owners were conducted monthly. The primary differences between the groups were the number of uremic episodes. These episodes were defined as an owner’s observation of 2 signs consistent with uremia (depression, lethargy,

Table 1. International Renal Interest Group (IRIS) Guidelines for primary classification of chronic renal disease Stage 1

Plasma creatinine (mg/dl) Dogs <1.4 Cats <1.6

Comments Non-azotemic Other renal abnormality present (inadequate concentrating ability, abnormal renal palpation, abnormal renal imaging)

2

Dogs 1.4 - 2.0 Cats 1.6 - 2.8

Mild renal azotemia. Clinical signs usually mild

3

Dogs 2.1 - 5.0 Cats 2.9 - 5.0

Moderate renal azotemia. Systemic clinical signs may be present

4

Dogs >5.0 Cats >5.0

Severe renal azotemia with extra-renal signs

anorexia, vomiting, stomatitis, and odoriferous breath), an increase in serum creatinine of more than 20% from the previous visit, and no possible alternative explanation for the signs and change in azotemia. No cats in the renal treatment diet group experienced a uremic episode compared to 6 cats fed the maintenance diet. The number of cats that died of CRF was also significantly lower in the renal treatment diet group (no cats) compared to the maintenance diet group (5 cats). In addition, the blood urea nitrogen was lower and serum bicarbonate was higher in the group fed a renal treatment diet. Nevertheless, when death from all causes was considered, there was no difference

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between the 2 diet groups. In addition, no differences were noted in body weight, hematocrit, urine protein-to-creatinine ratio, or serum concentrations of creatinine, potassium, calcium, and parathyroid hormone. The authors of the study concluded that the renal diet evaluated in this study significantly decreased both uremic episodes and renal related death. The International Renal Interest Group (IRIS) has created a standard staging for canine and feline chronic kidney disease (Table 1). This staging is becoming widely adopted and its use in clinical studies commonplace. Using this system, the chronic kidney disease patient is initially classified, based on their creatinine and then sub-categorized on the basis of proteinuria and blood pressure. Interestingly, this study did not strictly adhere to the IRIS staging guidelines. The correct time to switch a cat with CKD to a renal treatment diet has been debated for some time. This study provides evidence that cats with stage 2 (mild) CKD benefit from an appropriately formulated renal treatment diet. URINARY TRACT INFECTIONS IN CATS WITH HYPERTHYROIDISM, DIABETES MELLITUS, AND CHRONIC KIDNEY DISEASE Hyperthyroidism, diabetes mellitus, and chronic kidney disease are common dis-

eases in cats. Although diabetes mellitus and chronic kidney disease have been associated with urinary tract infections (UTIs), the idea that hyperthyroidism could increase the incidence of urinary tract infections has not been previously explored. A recent retrospective study2 attempted to evaluate the prevalence of UTIs in cats with these 3 common diseases and to identify associations between clinical signs, biochemical data, urine analysis, and urine culture results. Medical records for cats diagnosed over an 8-year period with either hyperthyroidism, diabetes mellitus, or chronic kidney disease were reviewed. Only patients that had urine collected by cystocentesis or catheterization for urine analysis and quantitative urine culture were included in the analysis. The records from 90 hyperthyroid cats revealed that 12% (11 cats) had positive urine cultures. None of the cats with positive cultures had clinical signs consistent with a UTI or abnormalities in the hemogram or serum chemistry. On urine analysis, 8 had microscopic evidence of bacteria, and only 2 had increases in white blood cells counts on urine sediment examination. The records from 57 cats with diabetes mellitus showed that 12% (7 cats) had positive urine cultures, but only 1 of the cats had clinical signs consistent with a

UTI. Five had microscopic evidence of bacteria, and 2 had increases in white blood cells counts on urine sediment examination. The records from 77 cats with CKD indicated that 22% (17 cats) had positive urine cultures. Four had clinical signs consistent with a UTI. Fourteen had microscopic evidence of bacteria, and 11 had increases in white blood cells counts on urine sediment examination. Of the 32 bacterial isolates identified, Escherichia coli (46%) and Enterococcus faecalis (27%) were the most common. Twelve percent of the isolates were resistant to amoxicillin/clavulanic acid, and 17% were resistant to enrofloxacin. Resistance to ceftiofur and cephalexin were common. The authors concluded that hyperthyroidism, diabetes mellitus, and CKD are often accompanied by UTIs, which may lack clinical signs and compatible urine analysis findings. This study presented interesting information regarding the occurrence of UTIs in hyperthyroid patients. In addition, it reinforces the important concept that urinary tract infections can occur in the absence of changes in the urine analysis or blood work. A significant number of the UTIs in this study were resistant to amoxicillin/clavulanic acid and enrofloxacin which are often used empirically. Therefore, a significant number of UTIs will be undiagnosed or improperly treated

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if urine cultures are not routinely submitted in these patients. REFERENCES 1. Ross, SJ, Osborne CA, Kirk CA, et al. Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats. J Am Vet Med Assoc 2006;229:949-957. 2. Mayer-Roenne B, Goldstein RE, Erb HN. Urinary tract infections in cats with hyperthyroidism, diabetes mellitus and chronic kidney disease. J Feline Med Surg 2006:9:124-132.

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