Anita Schwartz FAB's Resident at the University of Edinburgh looked at new approaches to treatment of this common feline disease at the FAB Conference, November 2008

Bailey, the Maine Coon, was housed in a large kennel to accommodate all that a kidney patient might need - IV drip, a water fountain, food, litter tray and, of course, a comfy bed

CHRONIC KIDNEY DISEASE(CKD) is a common cause of illness and mortality in feline patients. Approximately 10% of cats older than 10 years and 30% of cats older than 15 years suffer from CKD.

CKD is the progressive irreversible loss of kidney function resulting in renal failure. Normal kidneys are responsible for excreting waste products in the urine and maintaining fluid and electrolyte balance. If kidney function is decreased waste products such as urea and creatinine can accumulate in the blood. Healthy kidneys are able to regulate the body's fluid balance by concentrating the urine and therefore conserving water within the body. Diseased kidneys lose their urine concentrating ability and body water is lost. This can result in dehydration of the patient.

The kidneys are also responsible for the production of certain hormones. Therefore hormonal disturbance also plays a role in CKD.

The kidneys are organs with a great functional reserve. This means that initially kidney tissue can be lost without any clinically noticeable consequences for the cat. By the time clinical signs of CKD become apparent, about 75% of functional kidney tissue has been lost.

Acute renal failure (ARF) is the sudden loss of kidney function which is usually associated with severe systemic illness and can result in the death of the cat if not treated early on. Acute renal failure can be a reversible condition, but can also result in permanent damage of the kidneys if it is not treated aggressively early on. The resulting irreversible kidney damage will lead to CKD.

CKD is discussed here in more detail as it is a significantly more common problem in feline patients than ARF.

Causes of chronic kidney disease
The majority of cases of CKD are due to chronic interstitial nephritis (nephritis is inflammation of the kidney). This is an idiopathic (ie, of unknown origin) intrinsic degenerative disease and occurs mainly in older cats. It is thought that different causes can lead to this end point.

When signs of CRF are seen in young cats, congenital causes such as polycystic kidney disease of Persian cats or breed specific diseases like renal amyloidosis in Abyssinians should be considered. Cats with renal dysplasia are born with abnormally developed kidneys and can show signs of CKD.

Chronic renal failure can result from glomerular disease. The glomerulus is the microscopically small filter apparatus within the kidney and each kidney contains hundreds of thousands of glomeruli. This is,
however, much less common in cats than dogs.
Cancer of the kidneys such as lymphoma or adenocarcinoma and bacterial (pyelonephritis) or viral infections (eg, FIP) of the kidneys can also result in chronic renal disease. 

Causes of acute renal failure
Infections ascending from the bladder into the kidneys are regarded as a common cause of acute renal failure.

Nephrotoxis such as anti-freeze, all parts of lily plants, grapes and raisins can also result in acute kidney failure.

Certain drugs, eg, non- steroidal anti-inflammatory drugs (NSAID) and certain antibiotics can be harmful to the kidneys and can, especially when used in inappropriate doses, lead to acute renal failure.

Any condition that interrupts blood flow to the kidneys such as a significant blood loss or a state of shock with low blood pressure and therefore insufficient blood supply to the kidneys can lead to acute renal failure if it persists for long enough.

Cats suffering from chronic renal failure are prone to developing infections within their bladders which can develop into kidney infections, causing further kidney damage. Cats with CKD can easily become dehydrated if their water intake is not adequate for a period of time. Dehydration can also result in further renal damage. These acute insults on the already damaged kidney are called 'acute on chronic' crisis and often complicate CKD.

How to recognise CKD in your cat
Cats suffering form CKD often show very non-specific signs such as:

• Anorexia
• Lethargy
• Depression
• Polyuria (increased urination)
• Polydipsia (increased thirst)
• Vomiting
• Mouth ulcers (in severe cases)
• Melena (dark tarry faeces, in severe cases)
• Muscle weakness (in severe cases)
  

The physical examination by a veterinary surgeon can often identify further clinical signs:

• Dehydration
• Pale mucous membranes (eg, the gums)
• Small or enlarged kidneys (see opposite page)
• Hypertension (high blood pressure)
• Hypertensive retinopathy (bleeding into the back of the eye due to high blood pressure)

How to confirm the diagnosis
In order to be able to establish the diagnosis of CKD reliably, blood and urine tests have to be confirmed.
The finding of increased levels of waste products such as urea and creatinine in the face of decreased urine concentrating ability indicate kidney disease. Elevated levels of urea and creatinine (termed azotaemia) are not exclusively seen with kidney disease. It is therefore important to evaluate these findings together with an analysis of a urine sample, focusing on the urine specific gravity. The urine specific gravity (USG) indicates how well the kidneys are able to concentrate the urine. The normal diet of the cat (dry vs wet food) influences how concentrated the urine should be. A USG of greater than 1.035-1.040 is generally considered appropriate for a healthy cat. A USG below these levels together with the finding of azotaemia indicate kidney disease.

Reduced size of kidney suggestive of chronic kidney disease

Enlarged kidney on ultrasound suggestive of acute kidney disease

Severe or long standing kidney disease will result in further systemic changes which are reflected by blood test abnormalities. These include:

• Hyperphosphataemia (high phosphate levels in the blood)
• Hypokalaemia (low potassium levels in the blood)
• Anaemia
• Acidosis

Systemic hypertension (blood pressure greater than 160 -170 mmHg) is commonly found in cats suffering from CKD. Rather than being a cause of CKD, systemic hypertension is considered to be a consequence. High blood pressure can have serious effects on the cat's body. A common complication of hypertension is retinal bleeding which can lead to vision problems and in severe cases blindness. The blood pressure should therefore be measured in all cases of CKD and a retinal examination should be performed.

Imaging (X-rays or ultrasound scan) of the upper and lower urinary tract is also indicated. This can sometimes identify underlying problems responsible for the kidney disease such as kidney stones.

In rare cases it might be beneficial to obtain a kidney biopsy in order to be able to characterise the nature of the kidney disease better. In cases of suspected lymphoma for example this could be helpful in confirming the diagnosis and chemotherapy might be a treatment option. 

How to treat cats with CKD
Once the diagnosis of CKD has been established a treatment plan tailored to the specific needs of the individual patient can be formulated. The first step should always be the identification and treatment/removal of a possible underlying cause or contributing factor. One example would be a pyelonephritis which can be treated with antibiotics. If a treatable underlying cause cannot be found a number of medical treatments can be instituted:

Dietary management
Feeding a kidney diet is considered one of the most important treatments for cats with CKD. Many different kidney diets are available in both dry and wet forms. These diets are prescription diets and can be obtained through a veterinary surgeon. They are modified in order to meet the specific nutritional needs of cats with CKD.

• Restricted amounts of high quality protein - this lowers the amount of waste products resulting from protein break down.
• Restricted levels of phosphate
• Increased amounts of potassium
• Increased amounts of B-vitamins
• High calorie density
• Restricted amounts of sodium
  

It is important to remember that these diets should be introduced gradually, over days or even weeks. If a cat completely refuses to eat a renal diet, then a senior diet might be a good compromise. It is important that cats with CKD keep eating and therefore any food is better than no food!

Further phosphate restriction
The importance of phosphate restriction has been widely recognised and for severe cases the phosphate restriction provided by the renal diet might not be enough. In these cases the addition of phosphate binders to the food might be helpful. These substances bind the phosphate in the food and thereby prevent its absorption from the gut. Different phosphate binders are available from your vet, for example in the UK Alu Caps, Ipakitine and Renalzin.

Further potassium supplementation
Severe decreases in potassium can lead to marked muscle weakness. For those cases that develop
hypokalaemia, potassium in addition to the potassium provided in the kidney diet will have to be administered. This can either be achieved by adding potassium to intravenous fluids or by supplementing it orally. Examples for potassium supplements available from the veterinary practice are Tumil K and Kaminox.

Maintaining hydration
Maintaining good hydration is an important goal for the management of cats with CKD. Since urine concentrating ability is compromised in these cats they are at risk of dehydration. It is therefore important to ensure that they have access to fresh water at all times. An effective way of achieving increased fluid intake is feeding a wet rather than a dry food or adding additional water to the normal food. For cats that prefer running water a water fountain might be helpful in encouraging them to stay hydrated. Other methods such as offering flavoured water (avoid salty broths!), providing different types of water bowls or providing water from different sources (tap water vs bottled water) might result in cats drinking more readily.

For cats that fail to remain well hydrated, hospitalisation for intravenous fluid therapy or subcutaneous (under the skin) fluid administration at home might be necessary. Cat owners can be taught by a vet or vet nurse how to give subcutaneous fluids at home. Indwelling subcutaneous catheters can be placed under the cat's skin which might facilitate the administration of fluids.

Managing systemic hypertension
Managing high blood pressure which can be seen in cats with CKD is very important since this can have deleterious effects on the kidneys and other organs systems (eyes, heart, brain). The negative effects on the kidneys can result in worsening of the kidney disease. The aim is to keep the systolic blood pressure below 160 -170 mmHg. A calcium channel blocker called amlodipine (Istin) and ACE inhibitors such as benazepril (Fortekor) are commonly used for the management of systemic hypertension. 

Monitoring for urinary tract infections
Cats with CKD are at risk of developing bacterial bladder infections which can ascend into the kidneys if they remain untreated. This can complicate the existing renal disease. These cats might or might not show clinical signs of a bladder infection and it is therefore important to check their urine for evidence of cystitis on a regular basis. A urinalysis and urine bacterial culture should be performed. Antibiotic therapy will be required to clear a urinary tract infection.

Management of anorexia and vomiting
Cats with CKD can lose their appetite and suffer from vomiting for a number of different reasons. Several drugs including appetite stimulants (eg, Periaktin, Zispin) can be used to alleviate these clinical signs.

Cats suffering from CKD should have regular health checks including a physical examination, fundic examination, blood and urine tests and blood pressure measurement. Depending on the severity of the disease these check-ups should be performed every one to six months.

July 2009