Noninfectious Diseases of the Urinary System of Cats

The kidneys’ most important function is to filter waste from the blood. When this does not happen properly, waste products can build to dangerous levels in the blood. This is called azotemia. Azotemia can be caused by many factors, including dehydration, congestive heart failure (see Heart Disease and Heart Failure in Cats), and shock. Azotemia can also occur as a result of urine not being able to flow properly through the urinary tract.

The glomerulus is one of the structures that are essential for kidney function. It is made up of special blood vessels that help filter blood. Each kidney contains thousands of these structures. Glomerular disease sometimes causes kidney disease in cats. Damage to parts of the glomerulus can cause protein in the urine and low levels of a protein called albumin in the blood. This can lead to other problems, such as swelling of the legs, high cholesterol, and blood clots.

Glomerular disease can occur due to the longterm effects of high blood pressure. However, glomerular disease can also occur as a result of other disorders such as hyperadrenocorticism (an excess of cortisol) or amyloidosis. Some glomerular disease is immune-mediated, that is, caused by the cat’s immune system attacking parts of its own body.

Disease in the glomerulus often leads to protein in the urine, low levels of protein in the blood, a buildup of fluid in the abdomen (which can cause visible swelling), shortness of breath, and swelling in the legs. Taken together, these signs are called the nephrotic syndrome. (“Nephrotic” means relating to the kidneys.) The loss of protein through the urine can cause loss of muscle tissue. Most cats with glomerular disease eventually develop Stage III or IV kidney disease. Kidney disease that is accompanied by protein in the urine often leads to high blood pressure.

Your veterinarian will look for increased levels of protein and other chemicals in your cat’s urine and blood. Physical examination usually reveals that something is wrong; however, the signs are often nonspecific and could point to any of a wide variety of problems.

A biopsy of the kidneys is often required to determine the cause of the glomerular disease. Additional tests may be required in some cases, including x-rays, ultrasonography, and special blood tests.

Treatment for glomerular disease varies according to the underlying cause. In addition, kidney failure should be treated with appropriate medications (Veterinary.heading on page Noninfectious Diseases of the Urinary System in Dogs : Glomerular Disease).

Feline idiopathic cystitis is an inflammation of the urinary bladder of unknown origin. This condition has also been called idiopathic feline lower urinary tract disease (idiopathic FLUTD) and feline urologic syndrome. The cause is unknown, but certain factors such as viral infections, stress, diet, and genetic factors may play a role. Both male and female cats are affected.

Signs of feline idiopathic cystitis include frequent urination, blood in the urine, straining or distress while urinating, and urination in inappropriate locations. A urinary tract obstruction may occur in male cats due to their longer and narrower urethras; this should be considered a medical emergency and requires immediate veterinary attention. Signs of this condition include frequent unsuccessful attempts to urinate, lethargy, loss of appetite, and reluctance to move.

Diagnosis depends on a complete history and physical examination, as well as appropriate laboratory tests to identify feline idiopathic cystitis and exclude other conditions. These may include urinalysis and bacterial culture of urine, blood tests, x-rays, ultrasonography, and cystoscopy.

Treatment of this condition has many approaches. If bacteria are identified, antibiotics will be prescribed. Drugs that reduce pain and inflammation may be useful in some cases. Cats should have access to plenty of fresh, clean water to encourage water intake (so the cat will have less concentrated urine). Changing from a dry to a canned food may also help add water.

Another condition that may be related to—or the same as—feline idiopathic cystitis is called feline interstitial cystitis. Currently, it is unclear whether these are 2 separate conditions or whether they represent the same overall disorder. Signs of both conditions are similar and both involve inflammation of the bladder with bladder pain, straining, and bloody urine.

Renal tubules are structures in the kidneys that help filter blood. Healthy kidneys help the body to get rid of acid by producing urine that is very acidic. Diseased kidneys cannot get rid of acid properly, and instead of being eliminated in the urine, this acid builds up in the blood, leading to a condition called uremic acidosis. This condition can also occur when there are defects in the renal tubules, in which case it is called renal tubular acidosis. These defects are rare in cats. Treatment may involve medications to rebalance the amount of acid in the blood.

Even when the kidneys are functioning normally, a blockage in the urinary system at any point below the kidneys can lead to a backup of toxic wastes that can damage the kidneys and cause illness. In cats, the most common cause is a “plug” composed of protein, cellular waste, and/or crystallized minerals that blocks the urethra. Other possible causes include urinary tract stones (see Noninfectious Diseases of the Urinary System of Cats: Urinary Stones (Uroliths, Calculi)), tumors, or blood clots in the ureters or urethra.

If the flow of urine is blocked, the kidney becomes abnormally enlarged. When this happens suddenly to both kidneys, especially when the urine is completely blocked, the cat does not live long. When the blockage is only partial, or only occurs on one side, the cat often survives but the kidneys may sustain permanent damage. The affected kidneys eventually become giant, useless urine-filled sacs and may become infected. The ureter may also become enlarged due to a backup of urine. This often occurs when the blockage is located further down the urinary tract and away from the kidneys.

Cats with a urinary blockage will attempt to urinate frequently. These attempts, however, may be painful and will result in only small amounts of urine being produced. Often, blood will be present in the urine. An affected cat may have a painful abdomen, lose interest in food, and become more and more depressed. As the condition progresses, the cat may vomit and become dehydrated. Your veterinarian will be able to readily diagnose urinary tract obstructions based on the signs and a physical examination.

To restore normal urine flow, the blockage must be removed. In most cases, intravenous fluids will be used to restore the balance of various chemicals in the blood. Surgery is often required to resolve the blockage of the urinary tract.

If a cat has signs of a blocked urethra, it is critical to seek veterinary care immediately. Cats with a complete blockage may die within 2 to 3 days without treatment.

Tumors that originate in the kidneys and urinary tract are not common in cats. Tumors can be benign (harmless) or malignant (cancerous). Benign tumors, such as fatty tumors or tumors made of fibrous tissue, are usually discovered only by accident and do not require treatment.

Cancers that begin in other parts of the body may spread to the kidneys. (When cancer spreads from one organ to another, it is said to metastasize and the cancer itself is described as metastatic.) Metastatic tumors can appear on one or both kidneys. Lymphosarcoma is the type of tumor that most commonly spreads to the kidneys. Up to half of cats with cancer of the lymphatic system also develop cancer in their kidneys. In some cases, the cancer remains only in the lymph tissues and the kidneys; in others it also spreads to the brain. When cancer spreads to the kidneys, it usually takes the form of many small tumors. It can affect both kidneys and may cause the kidneys to become unusually large and irregularly shaped. Lymphosarcoma in cats frequently occurs along with infection with the feline leukemia virus.

Signs of kidney tumors are usually general and can point to many different illnesses. Common signs include weight loss, poor appetite, depression, and fever. Your veterinarian will need to eliminate other causes of these signs before confirming cancer. Occasionally, tumors that appear in both kidneys can cause enough damage that the cat will develop signs of late-stage kidney disease (see Noninfectious Diseases of the Urinary System of Cats : Chronic Kidney Disease and Kidney Failure).

Your veterinarian may suspect a tumor of the kidneys based on physical examination and careful consideration of your cat’s signs in the weeks and months prior to becoming ill. This suspicion can be confirmed with ultrasonography, x-rays, or contrast x-rays of the urinary tract. Cancer cells can also occasionally be found in the urine. A biopsy of the tumor is usually necessary to determine its type.

Normally, kidney tumors must be surgically removed. Usually it is necessary to remove the entire affected kidney. Tumors in the lymph nodes around the kidney are usually treated with chemotherapy instead of surgery. If your cat develops a urinary cancer, your veterinarian will assess the severity of your pet’s condition, the outlook for your pet, and other factors when recommending a treatment program. (For a more detailed discussion of tumors of the kidney and urinary tract, see Noninfectious Diseases of the Urinary System in Dogs : Tumors.)

Urination problems can be grouped into problems with storing urine and problems with eliminating urine. Urinary incontinence is the inability to prevent or control urination. Incontinent animals leak urine constantly or occasionally without realizing it. An incontinent cat may leave a pool of urine where it has been lying or dribble urine while walking. The fur around the vulva or penis may be wet, and the constant dribbling of urine can cause inflammation and urine scalding of the skin in these areas.

Uroliths are stones (also known as calculi) formed when minerals that naturally occur in urine clump together to form tiny crystals. These stones can develop anywhere in the urinary system, including the kidney, ureter, bladder, or urethra. Certain types of stones appear to have increased in cats in recent years. The cause is not clear, but researchers are looking at the effects of diet to determine if there is any link.

Veterinary researchers do not completely understand what causes stones to form (see Why Cats Develop Uroliths (Stones)). There are many different types of stones, each formed from a complex mixture of various minerals, and each of which develops only under certain conditions. They can be caused by a problem with the minerals themselves or by a problem with other chemicals that exist in urine and which, under normal circumstances, prevent stones from forming. The environment of the urinary tract may also contribute to stone formation. All of these conditions can be affected by urinary tract infections, diet, digestion, the amount of urine that a cat produces, how frequently a cat urinates, medications, and genetics.

Cats with very tiny stones in the urinary system do not usually have any signs. However, larger stones in the lower urinary tract may interfere with urination or irritate the lining of the urethra. In turn, these problems can cause an inability to urinate, blood in the urine, and slow or painful urination. Kidney stones (which are rare in cats) usually cause no signs unless the kidney becomes inflamed or the stones pass into the ureter. If a ureter becomes blocked by a stone, it can cause vomiting, depression, or pain in the abdomen in the area around the kidneys. Such pain is particularly common when both ureters are suddenly and completely blocked; the fluids back up causing the kidneys to become enlarged. Pain is the only sign of stones in the ureter on only one side; however, pain can be difficult to detect in cats. If the blocked ureter is not diagnosed right away, kidney damage occurs. Ultimately, the blocked kidney is destroyed.

Veterinarians can sometimes detect stones in the bladder by pressing on the cat’s abdomen. Stones in the urethra may also be detected during a rectal examination or when attempting to insert a catheter. There may be many stones present at once. If one stone is located, it is important to examine the entire urinary tract to look for others. X-rays can detect stones as small as 3 millimeters in size. Your veterinarian will also perform tests on the cat’s urine and may need to do ultrasonography or other specialized tests.

Treating stones, and preventing their return, depends on their type and location. Treatment and prevention may include surgery, a special diet, and medication. When stones are removed, your veterinarian may send them to a laboratory to be analyzed. Knowing what types of minerals are in the stone can provide the information needed to prescribe medication that can prevent the formation of more stones. Cats undergoing treatment for uroliths will need to be monitored closely, returning at regular intervals for additional testing.

Also see professional content regarding noninfectious diseases of the urinary system.