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Tag: Dr Remo Lobetti BVSc

Renal Disease In The Cat

| August 3, 2016

Dr Remo Lobetti BVSc (Hons) MMedVet (Med) PhD Dipl. ECVIM (Internal Medicine)

Veterinary Specialist Physician

 

THE NORMAL KIDNEY

 

The kidney is a multifunctional organ that controls conservation of fluid, removal of bodily wastes, and regulates calcium metabolism, red blood cell production, and electrolyte concentrations.

 

Normal anatomy of the kidney

 

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Conservation of fluid and removal of waste products

The kidney is made up of thousands of individual filtering units, each called a nephron. As blood passes through the kidney it is routed through each of these filters. In the nephron toxins and other wastes are removed, approximately 95% of the fluid is reabsorbed back to the bloodstream, electrolyte concentrations (primarily sodium, potassium, calcium, phosphorus, chloride) are delicately adjusted, and urine is produced. The urine then passes into the urinary bladder where it is stored until it is voided.

 

Bone and calcium metabolism

The kidney is responsible for providing precursor for the synthesis of vitamin D3, which is necessary for the absorption of calcium from the gastrointestinal tract. In addition, the regulation of concentrations of calcium and phosphorus is also determined by the action of parathyroid hormone, produced, by the parathyroid glands, in large part due to the kidneys’ response to excess circulating phosphorus. This hormone is responsible for adjusting serum calcium and phosphorus levels, primarily by activating removal of calcium from bone and promoting phosphorus excretion in the urine.

 

Red blood cell synthesis

The production of red blood cells by the bone marrow is stimulated by the presence of erythropoietin, which is produced by the kidney when red blood cells are in short supply and/or the delivery of oxygen to the tissues throughout the body is inadequate.

 

Blood pressure regulation

When blood pressure is low, there is a consequent decrease in filtered urine. The kidney, detecting this, triggers a cascade of biochemical events which result in sodium and fluid retention, a decrease in the diameter of blood vessels, and an increase in the heart rate and force of heart muscle contraction. These factors together increase the blood pressure throughout the circulatory system. Under normal circumstances, this process insures adequate blood pressure such that all important organs and tissues receive appropriate oxygen and nutrition, and the kidneys are able to process waste.

 

WHAT CAUSES KIDNEY DISEASE

 

The causes of renal disease and failure are numerous and in some instances, not fully understood. Renal failure may be either acute or chronic. Acute renal failure (ARF) is characterized by an abrupt shutdown of kidney function, most often accompanied by a severe reduced in urine production. ARF occurs at any age and if diagnosed and treated early, damage can in many instances, be arrested. In the majority of cases of acute renal failure where treatment is instituted early, the prognosis for full recovery is excellent. Chronic renal failure (CRF) appears to be common in geriatric cats. Although the damage is usually irreversible, the progression and severity of disease and the quality of life can be temporarily modulated with careful medical and dietary controls. CRF is a progressive, irreversible deterioration of kidney function. Because cats hide their illnesses and the early signs of CRF are subtle, this disease may only be recognized when the cat reaches a 70% deterioration level and more dramatic clinical signs are observable. The seemingly sudden onset may appear to be an acute condition but is most often a crisis point of CRF.

Age-related deterioration

As renal disease is progressive and CRF is one of the leading causes of illness and death in older cats, all cats over the age of seven should be annually screened for CRF by means of blood tests and urine analysis. With early detection, proper diet, and hydration, cats may remain happy and active for a long period of time before the inevitable decline.

 

Acute renal failure

The primary causes of ARF in cats are: urinary obstructions, infectious diseases, trauma, and the ingestion of toxins – the most common one being ethylene glycol which is contained in antifreeze. ARF is extremely serious and can quickly become fatal and therefore immediate veterinary treatment is imperative. Though the prognosis is usually poor, if damage has not been too severe and medical treatment is aggressive, it may be possible for normal kidney function to be restored.

 

Chronic renal failure

CRF may have one or more causes. The common contributing factors are age, genetics, environment, and disease. In recent years, more attention has been directed towards high blood pressure, low potassium levels, acidified diets, and dental disease as possible contributors to the development of CRF. Research has indicated that some breeds have a higher rate of CRF than others. The Maine Coon, Abyssinian, Siamese, Russian Blue, Burmese, and Balinese appear to be more likely to develop CRF than other breeds. Although CRF can occur at any age, it is usually a disease of older cats. With dietary improvements in cat food, advances in feline medical care and more cats living indoors, cats are now living much longer and their bodies eventually wear out just as human bodies do.

 

As many diseases can result in CRF and because there is no single, overwhelming cause of CRF, there is no definitive protocol for the prevention of CRF at this time. However, not all cats will develop CRF. In most cases, unfortunately, the usually diagnosis is simply CRF because the cause cannot be determined. Chronic renal failure occurs as an insidious, irreversible progression of damage to essential kidney structure which results in reduced function.

 

Chronic renal failure (picture from: Hill’s Atlas of Veterinary Clinical Anatomy, Hill’s Pet Products).

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Possible causes for CRF include:

  • Prolonged and unresolved ARF.
  • Prolonged and excessive stimulation of the immune system by any cause in any body system for any reason, resulting in the accumulation of “immune complexes” (antibodies and the substances they bind) in the circulatory system. When blood passes through the kidneys, some of these complexes deposit or “stick” to important kidney structures, seriously damaging these and thus diminishing the capacity and function of the kidney. Some common causes of chronic immune stimulation are:
    • persistent dental disease
    • chronic skin infection
    • chronic allergic dermatitis
    • chronic inflammatory bowel disease, pancreatitis
    • Diabetes mellitus.

Additional factors which may contribute to the progression of renal disease are:

  • High blood pressure
  • Abnormal electrolyte concentrations (sodium, potassium, chloride, calcium, phosphorus, magnesium)
  • Dehydration
  • Trauma
  • Improper diet:
    • acidifying diet
    • too much phosphorus, sodium, protein
    • too little potassium

 

CLINICAL SIGNS

 

Renal disease can only be accurately diagnosed with clinical tests. There are some clinical signs and behaviours that indicate the likelihood of renal disease and, if these are observed, the cat should be tested as soon as possible. The most telling signs are increased thirst and excessive urination. As the condition progresses, the cat may experience loss of appetite, nausea and vomiting, weight loss, poor hair coat and emaciation. As only 30% of kidney capacity is needed for normal functioning, the majority of clinical signs will be seen when approximately 70% of renal function is lost. Therefore it is important to begin treatment as soon as the first clinical signs appear.
Clinical signs associated with renal disease include (not all cats will exhibit all signs):

  • Excessive urination
  • Increased thirst
  • Nausea and gagging
  • Licking lips
  • Grinding or cracking sound in jaw
  • Vomiting (both clear/foamy liquid and food)
  • Drooling
  • Dehydration
  • Constipation
  • Loss of appetite
  • Weight loss
  • Muscle wasting
  • Emaciation
  • Poor hair coat
  • Halitosis (ammonia smell)
  • Lethargy
  • Eating litter
  • Weakness
  • Depression
  • Oral ulcers
  • Detached retina
  • Convulsion, low temperature, coma (end-stage)

DIAGNOSIS

 

There are several conditions, which exhibit clinical signs similar to those seen in CRF. Thus the only way to determine if renal failure is present is by laboratory testing. Urine analysis will determine if the cat’s urine is dilute, which indicates that the kidneys are not passing waste materials. Blood tests will determine the levels of creatinine and urea as well as other components of the blood. An elevated creatinine level is the most certain sign of loss of kidney function. Other tests that may be done are blood pressure determination and abdominal ultrasonography.

TREATMENT

Although there is no specific cure for CRF, the condition can be medical managed for a period of time. The cornerstone of CRF management is to control the amount of waste products that are sent through the kidneys. Since the remaining nephrons are limited in their ability to process waste, the idea is to reduce the amount of waste to a level that the surviving nephrons can accommodate. This is done through a combination of diet, medication, and fluid therapy. Additional therapy is treatment with angiotensin converting enzyme inhibitors (benazepril, enalapril), which dilate the blood vessels thereby decreasing blood pressure while facilitating a non-damaging increase in blood flow that does not tax the kidneys. More specific treatment is kidney transplantation and dialysis, both of which are now possible.

PROGNOSIS

CRF is a terminal disease and the only questions are how long and how well the cat will live until the end. With proper treatment, the cat may have from months to years of relatively high-quality life. As the cat’s caregiver(s), it is up to you to determine when the quality of life has decreased to a point at which prolonging life no longer has value.

As CRF progresses and toxin levels rise, cats become more uncomfortable with an overall sensation of feeling unwell. Human patients with a similar condition do not report “pain” but describe their condition as feeling poorly. Dehydration, in particular, can make the patient very uncomfortable. Aggressively treating CRF, especially with subcutaneous fluid therapy, should not be thought of as “prolonging the agony” as there is no significant pain associated with kidney failure until the end-stage. Even then, unless the patient convulses, the chief clinical signs will be malaise, weakness, nausea and discomfort.

 

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