THIS is the first of two articles about feline chronic kidney disease in which we will look first at the information we need to collect on a patient prior to treatment and then on the long-term conservative management of the condition. Chronic kidney disease (CKD) is a common condition of cats with an estimated prevalence of 1-3% (Brown et al, 2007). Although most commonly diagnosed in the elderly cat, it has been reported in patients as young as nine months old (DiBartola et al, 1987). Cats with kidney disease may have structural (e.g. polycystic kidney disease or nephrolithiasis) or functional disease; however, in many cases both are present. It is usually the functional impairment that results in clinical signs in the patient. Chronic kidney disease is diagnosed in a patient with any structural or functional abnormality that has been present continuously for three months or more. It is usually an irreversible disease and most often is progressive. It must be distinguished from acute kidney disease as the management and prognosis of the two conditions differ. This distinction is usually possible on the basis of a combination of the history and physical examination findings (see Table 1). In some cases CKD may be complicated by concurrent pre-renal and post-renal components or active kidney disease (such as pyelonephritis) that may be reversible. Correction of these components or primary diseases may result in improvements in renal function but after this correction, further improvements in renal function should not be expected. When chronic kidney disease is diagnosed, the next step is to stage the disease. Staging cats with CKD is useful both to establish a prognosis as well in managing these patients. Staging is performed using the International Renal Interest Society (IRIS) classification system (www.iriskidney.com) which is based on the serum creatinine concentration, proteinuria and blood pressure (see Tables 2, 3 and 4). The serum creatinine (measured in a fasted, well hydrated patient) is used to stage the level of kidney function of stable patients. It should be measured in at least two samples collected over a period of 1-2 weeks. The degree of proteinuria should be determined in samples with inactive urine sediment (i.e. in samples with no evidence of haematuria, inflammation or infection) and should be confirmed to be persistent.
Underlying causes not identified
Likewise, arterial blood pressure should be determined several times over a few weeks to determine the blood pressure classification prior to treatment (unless there is evidence of retinal lesions or neurological signs or the blood pressure is over 200mmHg, in which case treatments should be initiated immediately). In many feline patients, the underlying cause(s) of chronic kidney disease are often not identified at the time of diagnosis, because they tend to be diagnosed relatively late in the
disease process. It is likely that susceptibility factors such as increased age, fewer nephrons at birth and genetic factors combine with initiating factors such as infections, nephrotoxicity,
hypertension and hypoperfusion, leading to kidney damage. Progression factors including proteinuria, elevated serum phosphorus concentrations and hypertension then lead to worsening of kidney damage, resulting in a gradual decline in
the glomerular filtration rate. In a study in cats with renal
azotaemia, 70% had tubulointerstitial nephritis, 15% had glomerulonephropathy and 2% had amyloidosis (Minkus et al, 1994). The initiating causes of diseases thought to originate in the tubulointerstitium have been particularly difficult to identify. Nevertheless, attempts to identify the underlying cause (e.g. pyelonephritis, renal lymphoma, nephrolithiasis and hypercalcaemia) and determine if it is still active should be made. Although treatment for these causes will be unlikely to reverse the existing damage, it may minimise further nephron loss. The next step is to identify clinical, biochemical and haematological
consequences of CKD such as dehydration, uremic stomatitis, uremic gastritis, hyperphosphataemia, calcium and electrolyte imbalances and anaemia. The management and treatment of these complications will help both in improving the patient’s quality of life and slow the progression of the disease.
Unrelated conditions not uncommon
Finally, as the median age of cats with CKD is 12.6 years (Elliott and Barber, 1998), other unrelated concomitant conditions are not
uncommon in these patients. The presence of comorbid conditions
should be identified. Examples of conditions that should be considered are hyperthyroidism, cardiac disease, dental/oral disease or degenerative joint disease. The presence of these
conditions might affect the long-term management of the CKD patient. In order to obtain all the above information, the initial diagnostic database for cats with CKD is likely to include: a full medical history, physical examination (including ocular examination), a serum biochemistry profile (including urea, creatinine, albumin, globulin, electrolytes, calcium, magnesium and phosphorus), urinalysis (including urine protein-to-creatinine ratio), urine culture and sensitivity, haematology, blood pressure
measurement, abdominal ultrasound and/or abdominal radiography. Additional diagnostics in selected cases might include the measurement of total thyroxine concentration, acid base status, parathyroid hormone concentration and renal biopsy. By definition, CKD is an incurable contion and in most cases it is also progressive; however, this disease tends to progress more slowly in cats than in dogs. Appropriate treatment has been shown both to improve the quality of life of these patients as well as modify disease progression. Many cats with CKD survive for years following diagnosis and some die of other diseases before their CKD becomes terminal.
- The second article will focus on the long-term management of feline CKD patients.
References
Brown, S. A. (2007) In: Elliott J, Grauer G.F. eds. BSAVA Manual of canine and feline nephrology and urology, 2nd edition. BSAVA, Gloucester. DiBartola, S. P., Rutgers, H. C., Zack, P. M. and Tarr, M. J. (1987) Clinicopathologic findings associated with chronic renal disease in cats: 74 cases (1973-1984). J Am Vet Med Assoc
190: 1,196-1,202. Minkus, G., Reusch, C., Hörauf, A., Breuer, W., Darbès, J., Kraft, W. and Hermanns, W. (1994) Evaluation of renal biopsies in cats and dogs – histopathology in comparison with clinical data. J Small Anim Pract 35: 465- 472. Elliott, J. and Barber, P. (1998) Feline chronic renal failure: clinical findings in 80 cases diagnosed between 1992 and 1995. J Small Anim Pract 39: 78-85.
Further reading
Polzin, D. J. (2011) Chronic kidney disease. In: Bartges J. and Polzin D.J. eds. Nephrology and Urology of Small Animals, Wiley-Blackwell, Chichester.
