Kidney Filtration Problems in Cats

Nephrotic Syndrome in Cats

One of the body’s main methods for disposing of waste products is through the establishment and formation of urine. This process occurs in the kidney, where penetrable clusters of capillaries called glomeruli function to filter waste from the blood, thus establishing the formation of urine. When filtration cells (podocytes) in the kidney’s glomeruli become damaged, due either to immune complexes in the blood (called glomerulonephritis), or to dense deposits of hard protein (amyloid) - the abnormal accumulation of which is called amyloidosis - degeneration of the kidney’s tubular system occurs. This degeneration of the tubular system is medically referred to as nephrotic syndrome. Patients with nephrotic syndrome lose too many necessary proteins into the urine; a condition medically termed as proteinuria. Two of these proteins are albumin, which helps to maintain blood pressure and keep blood in the vessels, and antithrombin III, which prevents blood clots from forming.

When greater than 3.5g of proteins are lost each day, blood pressure falls, and less blood stays in the blood vessels. Consequently, the kidneys act to conserve sodium in the body, which results in swelling of the limbs, hypertension and fluid accumulation in the abdominal cavity.

When crucial thyroid proteins, which control the body’s metabolic rate, are also lost into the urine, signs of hypothyroidism can also be seen. There is a decreased break-down of cholesterol, and the affected cat will often show signs of muscle wasting. In addition, the liver also increases its production of proteins and lipids, further raising the levels of cholesterol-rich lipids circulating in the blood. This can lead to arteriosclerosis, diminished blood circulation due to thickening, and hardening of the arterial walls. Also, since proteins essential for breaking down blood clots are lost into the urine, the blood coagulates much more easily and blood clots can become lodged in blood vessels, causing paralysis or strokes.

If left untreated, progressive glomerular disease can lead to urea nitrogen and creatinine (a metabolic waste product) accumulation in the bloodstream. That is, the accumulation of metabolic waste products in the bloodstream, which could lead to long-term kidney failure. This disease is relatively rare in cats.

Symptoms and Types

• Swelling of the limbs
• Fluid accumulation in the abdomen, abdominal enlargement
• Retinal: detachment or hemorrhage due to high blood pressure
• Swelling of the optic nerve (at the back of the eye) due to high blood pressure
• Heart rhythm disturbances due to enlargement of the left ventricle of the heart
• Difficulty breathing
• Bluish-purple skin color

Causes

Long-term inflammatory conditions which could predispose cats to developing glomerulonephritis or amyloidosis:

• Infection
• Cancer
• Immune-mediated disease

Diagnosis

Your veterinarian will perform a thorough physical exam on your cat, along with a complete blood profile, including a chemical blood profile, a complete blood count (CBC), an electrolyte panel, and a urinalysis. You will need to give a thorough history of your cat's health, including a background history of symptoms. The history you provide may give your veterinarian clues as to which organs are being affected secondarily.

Protein electrophoresis may help to identify which proteins are being lost into the urine through the kidneys so that a prognosis can be established. X-ray and ultrasound imaging will show if there has been a loss of detail in the abdominal cavity due to fluid seeping into the abdominal cavity (effusion). If glomerular disease is the cause of the nephrotic syndrome, mild enlargement of the kidneys may also be observed.

Treatment

The majority of patients can be treated on an outpatient basis, but if your cat is showing signs of severe nitrogenous waste in the bloodstream (azotemia), high blood pressure (hypertension), or blocked vessels due to clotting (thromboembolic disease), it should be hospitalized. Your veterinarian may prescribe medication to stop the loss of protein into your cat's urine and increase blood pressure.

Living and Management

You will need to limit your cat's activity in order to prevent thromboembolic disease. A low-protein, low-sodium diet, perhaps one that is specially formulated for strengthening the kidney, should be fed to your cat. Your veterinarian will assist you in creating the best diet plan for your cat.

Your veterinarian will schedule follow-up appointments for your cat at one month after the initial treatment, and then again at three month intervals for the year following. At each visit, a chemical blood profile, a urinalysis, and an electrolyte panel will be performed. The chemical blood profile is useful for monitoring kidney function, and the urinalysis will indicate the amount of protein being lost into the urine. Your doctor will also take your cat's blood pressure and monitor its weight at each visit.

Glomerulonephritis and amyloidosis are progressive. If the underlying cause cannot be resolved, your cat will eventually lose all kidney function. The prognosis for end-stage kidney disease is poor.