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Chronic kidney disease and degenerative joint disease in cats

Marino CL, Lascelles BDX, Vaden SL, et al. Prevalence and classification of chronic kidney disease in cats randomly selected from four age groups and in cats recruited for degenerative joint disease studies.  Journal of Feline Medicine and Surgery 2014;16:465-71.

Many older cats with chronic kidney disease (CKD) also have concurrent degenerative joint disease (DJD), but this may also be the case in younger cats as well.  In this retrospective study, these syndromes were studied in two cohorts of cats: the first (RS cohort) was composed of randomly selected cats, patients of a single feline-only practice in the USA, from four age groups ranging from 6 months to 20 years. The second (DJD cohort) comprised cats recruited from previous DJD studies of reduced activity or impaired mobility conducted at the same institution. This cohort was subdivided into 2 groups based on blood urea nitrogen (BUN) and/or serum creatinine concentration (subgroups A and B, BUN and serum creatinine
< 20% above the upper limit of the reference interval; subgroups C and D, serum creatinine < 2.8 mg/dl); therefore cats with the most severe CKD were excluded from the DJD cohort. All cats in both cohorts were spayed females or castrated males. As measurement of glomerular filtration rate (GFR) in companion animals is still mostly an academic exercise, serum creatinine concentration is generally used as a marker of GFR. The International Renal Interest Society (IRIS) staging system for stable CKD in animals is principally based on serum creatinine concentration, although other markers of renal function are included, and is used to determine prognosis and treatment recommendations for feline and canine CKD patients.  The goals of this study were to determine the prevalence of CKD in the RS and DJD cohorts, to determine the concurrence of CKD with DJD in the DJD cohort, and to classify CKD in all of the patients based on the IRIS staging system.

The RS cohort was subdivided into 4 groups based on age:  6 months-5 years (“immature”); 5-10 years (“mature”); 10-15 years (“senior”); and 15-20 years (“geriatric”).  Each group contained 25 cats selected randomly by a computer from a larger group of the same age, and the cats so selected were brought into the research team for a health screen.  All of the cats received a body condition score, physical, orthopedic, and neurological examinations, routine laboratory screening (complete blood count [CBC], biochemical panel, and urinalysis), and sedated orthogonal radiographs of all appendicular joints and spinal segments.

The DJD cohort included 128 cats. All of the cats enrolled in the DJD cohort were indoor only, had received no anti-inflammatory medications for 4 weeks prior to the study, had no clinically significant changes in CBC or serum chemistry for 4 weeks prior to the study, and had demonstrated mobility impairment based on a client-specific outcome measures form. A board-certified veterinary radiologist reviewed the radiographs of all cats, which included all cats in the RS cohort and the vast majority of cats in the DJD cohort, for renal abnormalities.  Patients’ kidneys were not evaluated ultrasonographically, which is a significant limitation of this study, nor were the patients assigned an IRIS substage based on blood pressure and urine protein-to- creatinine ratios, because these parameters were not measured.

Ultimately only 86 cats were evaluated in the RS group; 14 cats were excluded either because a urine sample was not obtained or the renal silhouettes were not visible on their radiographs. Of the RS cats included in the study, 50% (43/86) were determined to have CKD. These patients were mostly mixed breed; 19 were purebred cats of various breeds. Prevalence of CKD, usually IRIS stage I or II, was surprisingly high in the 3 youngest age groups, ranging from 37.5% in the 6 months-5 years group, to 40.9% in the 5-10 years group and 42.1% in the 10-15 years group.  In the 15-20 years group, 80.9% had CKD, IRIS stages I through III.

In the DJD cohort, 8 cats were in the immature group; there were 32 mature cats, 59 seniors, and 29 geriatrics.  Most cats were mixed breed; 18 were purebred, representing various breeds. In this cohort the prevalence of CKD (68.8%) was even higher than in the RS cohort, with 45.3% of these cats in stage II CKD. Although the sample sizes in this study were relatively small and the selection methods for the patients in the RS and DJD cohorts were different, there appears to be a strong concurrence between CKD and DJD in cats, even younger ones, and this is an important consideration when evaluating a cat with DJD for possible non-steroidal anti-inflammatory (NSAID) therapy.

The explanation for co-prevalency of CKD and DJD in cats is unknown. It is possible that as the cats in the DJD cohort were presented for changes in activity level, concurrent occult CKD could have contributed to this.  Another possibility is that CKD and DJD have a shared etiology; maybe inflammation or immune dysfunction contributes to the simultaneous development of both conditions.  Interestingly, in traditional Chinese medicine (TCM), an age-old system of diagnosis and treatment now being applied to companion animals as well as continuing its historic use in humans and horses, and which is controversial in terms of evidence-based support, the skeletal system and kidneys are both encompassed by the “water” element, so decompensation in one of these systems might be expected to associate with disease in the other, although this paradigm still provides no straightforward etiological explanation. [PJS]

See also:
Lascelles BDX, Robertson SA.  DJD-associated pain in cats: what can we do to promote patient comfort?  Journal of Feline Medicine and Surgery 2010;12:200-12.

Polzin DJ. Evidence-based step-wise approach to managing chronic kidney disease in dogs and cats.  Journal of Veterinary Emergency and Critical Care 2013;23:205-15.