Chronic kidney disease (CKD) or chronic kidney disease (CRF) is a loss of metabolic, endocrine, and excretory functions of the kidneys; it is present in 2 to 5% of dogs.
It is generally an old dog pathology. It is an insidious disease because the loss of kidney function takes months or even years. Compensatory mechanisms are put in place by the body to compensate for the loss of functional nephrons. The first clinical signs appear after a loss of 75%.
The causes of chronic kidney disease are diverse, they can be hereditary, congenital or following a disease ( Leptospirosis, amyloidosis).
Clinical signs of Chronic Kidney Disease
During CRF, the functioning nephrons are replaced by scar tissue and can no longer fulfill their role. This loss leads to an adaptation of the rest of the nephrons and a compensation to maintain the homeostasis of the organism (homeostasis is the capacity that a system may have to maintain its operating equilibrium despite the constraints which are external to it).
The International Renal Interest Society (IRIS) has established 4 stages of renal failure. These stages are not perfectly well defined, but correspond to phases in the degenerative process of renal function. They are based on the level of plasma creatinine (Table). Thus, a blood test makes it possible to determine at what stage of CRF the dog is and to set up the appropriate treatment.
The consequences of kidney disease are mainly related to urea. Urea is broken down by bacteria into urease and ammonia which will attack the tissues.
There is an over-stimulation of the production of acid by the stomach because the elimination of gastrin (hormone regulating stomach acidity) is no longer carried out by the kidneys which leads to stimulation of the vomiting center at the cerebral level.
Other gastrointestinal signs may be observed: stomatitis, diarrhea, anorexia, halitosis, ulcers and intestinal paralysis.
The loss of renal function will lead to high blood pressure through activation of the renin-angiotensin-aldosterone system, increased capillary permeability and the formation of pulmonary edema. This arterial hypertension can have other consequences: retinal detachment and left cardiac hypertrophy.
The hematology of the dog with chronic kidney disease is also changed. The function of neutrophils and the cell-mediated response is reduced, which will promote secondary infections. Platelets are altered and hemostasis disorders are observed (petechiae, bruising, bleeding gums). Non-regenerative normochromic normocytic anemia is observed with CRF.
The kidneys are involved in regulating the body’s acid-base balance, so in chronic kidney disease metabolic acidosis can set in and precipitate damage. The kidney no longer plays its role in the excretion of phosphorus, which increases the risk of secondary hyperparathyroidism.
Finally, a consequence frequently observed is damage to the central nervous system by urea. There are diffuse and non-specific alterations in the cerebral cortex. The nervous signs observed are varied: decreased alertness, lethargy, tremors, stupor, behavioral disturbances, muscle weakness, ataxia, cramps, convulsive fits and coma.
The diagnosis of CRF is usually made at an advanced stage of the pathology. The animal is often seen by the veterinarian because it is vomiting, or has bloody diarrhea, is listless or no longer eating. He urinates more, even “forgets” inside. A blood test will allow him to check creatinemia, uremia and phosphatemia but also the blood count. This blood test will not only allow him to make a diagnosis, but also to see at what stage of pathology the dog is (IRIS classification) and to adapt his treatment and prognosis accordingly.
The diagnosis of CRF can be made earlier in old dogs, especially during a routine blood test. An increase in creatinine will guide the veterinarian. Faced with a breed at risk, offering a urine analysis, and measuring the protein / creatinine ratio will make it possible to check that everything is fine, or whether the dog should be monitored or even put on an appropriate diet, this before the appearance of clinical signs.
Treatment of Chronic Kidney Disease
The goals of treating chronic kidney disease in dogs are:
SLOW THE EVOLUTION OF THE DISEASE (and not treat it).
- prevent anorexia and weight loss
- maintain glomerular filtration
- prevent the development of secondary hyperparathyroidism
- limit the production of uremic toxins.
- manage complications (BP, protein losses in the urine, etc.)
The main treatment for CRF is diet. Good kidney nutrition helps achieve these goals.
Protein intake must be restricted so as not to increase the quantity of nitrogenous waste but of very good quality so as not to starve the dog. The kidney diet will be richer in lipid, which will promote energy intake but by reducing the volume of food and therefore reduce stomach distension during meals and thus the risk of nausea and vomiting. Sodium intake will be normal or even slightly reduced to limit the risk of hypertension, but not removed to avoid any risk of cellular imbalance. The phosphorus intake will be reduced. Water-soluble vitamins are strongly excreted by the kidneys during polyuria, their amounts will be increased.
The omega3 / omega6 ratio must be balanced, as well as the intake of vitamins E and C, taurine and carotenoid pigments. They have a role as antioxidants.
The fiber intake must be sufficient to help intestinal motility, but also to increase bacterial biomass and reduce renal excretion of nitrogenous waste by increasing faecal excretion.
The rest of the treatment for chronic kidney disease is aimed at avoiding secondary pathologies.
The administration of ACE inhibitors and calcium channel blockers will help limit hypertension.
Phosphorus chelators can be added if the phosphatemia is still too high.
If the gastrointestinal system is affected, anti-emetic drugs and proton pump inhibitors may be prescribed to prevent nausea. Intestinal dressings will be helpful in the case of diarrhea.
Finally, in the event of anemia, the administration of androgens, a blood transfusion or the administration of EPO may be considered.
Treatment outcomes and prognosis
The animal in chronic renal failure is an animal which must be followed and have a regular evaluation of its state (creatinemia, uremia, weight), thus the adjustment of the treatment can be considered (figure).
Chronic kidney disease is a progressive disease that inexorably leads to the death of the dog. The goal of treatment is to provide the dog with the best possible quality of life.
The prognosis depends on the severity of the clinical signs and the serum creatinine concentration (Table).
In stage IV, the phase of the uremic syndrome, dietetic treatment and medication are no longer sufficient, and euthanasia is often the last alternative.
Chronic kidney disease is an irreversible degeneration of the nephrons, clinical signs appear when three-quarters of the kidney mass is no longer functional. CRF is the third leading cause of death in dogs.
Early detection (control blood test) is important and helps delay the onset of clinical signs. Regular monitoring of the animal makes it possible to check compliance with the treatment, to adjust it and possibly to treat other concomitant pathologies.