Noninfectious Diseases of the Urinary System of Cats

Longterm, or chronic, disease can damage the kidney so severely that it is not able to function properly. This happens slowly. Chronic kidney disease often continues for many months or years before a cat has any signs. There is rarely anything that a veterinarian can do to treat existing damage. Occasionally, chronic kidney disease results from a problem that is inherited or an abnormality present at birth. Some breeds of cats are more likely to have this problem; however, most of the time it is a problem related to old age. Starting at age 5 to 6, chronic kidney disease becomes more common, affecting up to 35% of elderly cats. Chronic kidney disease that is not inherited does not seem to be more common among certain breeds or among males or females.

Veterinarians classify chronic kidney disease into 4 stages based on laboratory tests, the cat's signs of disease, and the results of physical examinations ( see Table: Chronic Kidney Disease Stages). In Stage I, the kidneys are damaged but azotemia (a buildup of toxins caused by poor filtering of the blood by the kidneys) has not yet developed and the cat has no signs. This is the stage at which treatment has the greatest chance of success. However, because the cat has no signs, the disease is rarely diagnosed at this stage. In Stage II, the kidneys filter waste much more slowly than normal, and there is a buildup of waste chemicals in the blood, but most cats still have no signs. Signs that may be present at this stage include an increase in the amount of water in the urine and an increased volume of urine. In Stage III, filtering slows even more, the waste chemicals are more concentrated in the blood, and the cat develops signs of disease. Stage IV, the final stage, reflects continued kidney damage and accumulation of waste products in the blood. By this time, the cat feels and acts very sick.

Veterinarians further classify cats with kidney disease based on the presence of high blood pressure or protein in the urine. About 20% of cats with longterm kidney disease have elevated blood pressure (hypertension), which can cause further damage to the kidneys and also injure the eyes, brain, heart, and blood vessels. The risk of damage to the kidneys and other organs increases as the blood pressure increases. The presence of protein in your cat's urine can indicate that your cat has or may develop kidney disease, body-wide inflammation, metabolic disease, cancer, or infectious diseases. Your veterinarian will perform urine tests to learn how much protein is present, to help determine your cat's treatment and chances of recovery.

Determining the cause of chronic kidney disease, especially in the early stages, will help determine the appropriate treatment and outlook for your cat. Some of the common causes include diseases of the circulatory system (such as high blood pressure, problems with blood clotting, and not having enough oxygen in the blood) or other diseases of the kidneys such as pyelonephritis, obstructions caused by urinary stones, or tumors. Any injury to the kidney can also cause longterm kidney disease. Whatever the cause, chronic kidney disease usually results in scarring of the kidneys, which gets gradually worse.

Cats usually have no signs of kidney disease until they are at Stages III or IV, when their kidneys are working at less than 25% of their usual capacity. Exceptions to this are cats with other illnesses that affect the entire body or kidneys that become unusually inflamed or sore and cause vomiting or pain. Veterinarians may be able to detect a problem in a blood test or on physical examination even before the cat develops signs of kidney failure. Usually, the earliest signs are excessive thirst and urination. However, these signs may signal other diseases as well, and they do not begin to appear until Stage II or III. As the disease progresses over months to years, other problems begin. These include loss of appetite, weight loss, dehydration, sores in the mouth, sluggishness, vomiting, and diarrhea.

To diagnose chronic kidney disease, veterinarians generally use a combination of x-rays, ultrasonography, urine and blood tests, blood pressure measurement, and physical examination. These tests are also used to check the response to treatment and monitor complications related to the kidney disease.

With proper treatment, even cats with as little as 5% of normal kidney function can survive for a long time. The recommended treatment depends on the stage of disease. Identifying and treating complications, such as high blood pressure or urinary tract infections, needs to be done as well. During all stages of disease, it is important to provide continuous access to water and encourage adequate food intake. All cats with kidney disease should see their veterinarian every 6 to 12 months, or more frequently if there are problems. During these visits, the veterinarian will assess body weight and hydration, measure blood pressure, and do tests on the cat’s blood and urine.

Cats in Stages 2 and 3 should see the veterinarian every 3 to 6 months. During these stages, veterinarians may begin recommending urine cultures every year, or more frequently as needed. Urinary tract infections are common in cats with kidney disease and can worsen kidney damage. Depending on the findings of the physical examination and laboratory tests, medications often become necessary during these stages. A commercial diet developed for cats with chronic kidney disease may also be recommended.

In the later stages of kidney disease (III and IV), the cat should be taken to the veterinarian every 1 to 3 months. At this stage, treatments will focus on easing some of the signs of the disease with appropriate medications. Your veterinarian may teach you to administer subcutaneous fluids (fluids injected under the skin). Sometimes veterinarians will recommend intravenous fluids or feeding tubes. If these supportive measures do not improve your cat's signs, there are very few options and euthanasia may have to be considered. Dialysis machines, which do the job of the kidneys by filtering the blood, can prolong life, but dialysis is not feasible for most pets. A kidney transplant is rarely done and requires immune-suppressing drugs to prevent the body from rejecting the new kidney, which can cause other problems.

Acute (short-term or sudden) kidney injury is the result of sudden, major damage to the kidneys. This damage is usually caused by toxic chemicals either consumed by your pet or built up by an abnormal condition in your pet’s body. Kidney function can also be affected when the kidneys do not receive sufficient oxygen, such as when a blood clot blocks the flow of blood to the kidneys. Some types of infections can also cause an acute kidney injury.

Some cats may consume toxic chemicals, such as antifreeze, or poisonous plants that can damage the kidneys. Certain medications, such as nonsteroidal anti-inflammatory drugs or certain antibiotics, can also cause kidney damage. There are many substances and foods in the average home that may be safe for humans but dangerous for cats and other pets ( see Introduction to Poisoning). For example, ingestion of a small amount of any part of a lily (flower, leaf, pollen, or water) can cause a severe kidney injury in cats. Some toxic chemicals come from inside the cat’s body. For example, a buildup of calcium or other substances can occur due to disease in another part of the body. The effects on kidney function can last from 1 to 8 weeks, depending on the chemical(s) that caused the injury.

Mild kidney injuries often go unnoticed. However, repeated occurrences or a severe injury can lead to chronic kidney disease. The 4 (I through IV) stages of acute and chronic kidney disease are the same (see above). Usually, acute kidney disease is not detected until Stage IV, when signs can include loss of appetite, depression, dehydration, sores in the mouth, vomiting, diarrhea, and urinating a smaller than normal volume of urine.

It is important to determine whether the kidney disease is acute or chronic, as well as the cause of the disease. This information will help your veterinarian determine the most appropriate treatment. If your veterinarian can determine what caused the kidney injury, treatment will be aimed at this cause. Cats that are dehydrated or not eating may require intravenous fluids or a feeding tube. Other medications may also be necessary. If none of the available treatments work, and your cat is simply not producing urine, the only remaining options are kidney dialysis, a kidney transplant, or euthanasia.

Severe kidney injuries are life threatening, and only about half the affected animals will survive. However, the kidney does have the ability to regain function if the cat can survive the episode.

Benign tumors, such as fatty tumors (lipomas) or tumors made of fibrous tissue (fibromas), are usually discovered only by accident and do not require treatment. They usually do not affect the health of the cat.

The most common malignant kidney tumor is a carcinoma that starts in the lining of the renal tubules. Usually, the tumor appears on only one kidney. Cancerous tumors that begin in the kidneys spread quickly to other organs, especially the opposite kidney, the lungs, adrenal glands, and the liver.

Blastomas are tumors composed of previously healthy young cells that never mature normally. Instead, these cells mutate into cancer. Those that originate in the kidney are known as nephroblastomas. (Other names for this type of tumor are embryonal nephroma and Wilms tumor). These types of tumors are seen in young animals. Nephroblastomas usually occur in only one kidney, but occasionally they affect both kidneys. They can become quite large; a single nephroblastoma can take up almost all of the space inside the affected cat’s abdomen. Nephroblastomas typically spread to nearby lymph nodes, the liver, and the lungs.

Transitional cell tumors are cancers that appear in the lining of certain parts of the urinary tract, including the ureter, bladder, urethra, or the center of the kidney (referred to as the renal pelvis). Other malignant tumors rarely originate in the kidneys, but can include hemangiosarcomas (tumors from the lining of the blood vessels), fibrosarcomas (tumors of connective tissue), leiomyosarcomas (tumors of the smooth muscle), and squamous cell carcinomas (tumors of the outer layer of the kidney surface).

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 in one or both kidneys. Lymphosarcoma is the type of tumor that most commonly spreads to the kidneys. Up to half of cats with this 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 or other tissues. 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. Some cats will develop "lumps" within the abdomen or general enlargement of the abdomen. Blood in the urine may also occur. 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 above).

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. Lymphosarcoma is 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.

Tumors in the ureters, bladder, and urethra are rare in cats. The average age of affected cats is 9 years old. Tumors that develop in the lower urinary tract are more likely to be malignant than benign. Benign tumors that can be found in the lower urinary tract include papillomas (warts; tumors of the lining of organs), leiomyomas (smooth muscle tumors, also called fibroids), neurofibromas (tumors of the protective sheath that surrounds nerves), hemangiomas (blood vessel tumors), rhabdomyomas (another type of smooth muscle tumor), and myxomas (tumors of primitive connective tissue).

The most common type of malignant tumor that begins in the lower urinary tract is a transitional cell carcinoma. Transitional cell carcinomas are cancers that appear in the lining of certain parts of the urinary tract, including the ureter, bladder, urethra, prostate, and renal pelvis. Transitional cell carcinomas may appear as a single tumor or as multiple, wart-like growths visible on the membranes lining the urinary tract. Alternatively, these carcinomas may develop all over the ureter, bladder, prostate gland, or urethra. Once they appear, they have the tendency to grow and spread quickly, most often to the nearby lymph nodes and lungs.

Tumors in the ureter and bladder can cause blockage of urine, which can back up into the kidneys and cause damage. Tumors in the urethra are more likely than tumors in the ureter and bladder to suddenly cut off the passage of urine. Tumors in the bladder and urethra may be accompanied by urinary tract infections that will not go away despite treatment with antibiotics.

The most common signs of cancer of the lower urinary tract include blood in the urine; painful, slow, or difficult urination; and excessive urination. Cats with one blocked ureter may have a painful abdomen, and a veterinarian may be able to feel an enlarged kidney. Cats with blocked ureters on both sides or a blocked urethra may show signs of uremia (a buildup of the toxic chemicals usually eliminated in the urine). While doing an examination, a veterinarian may be able to detect a thickened bladder wall, an irregular urethra, or masses on the urethra.

Laboratory tests on the cat’s urine usually reveal blood in the urine, and they sometimes reveal a bacterial or other infection that has developed in addition to the tumor. Sometimes, cancer cells can be found in the urine, especially when the cancer is in the transitional cells. Your veterinarian may use ultrasonography or specialized x-rays to locate and assess the severity of the tumor. A biopsy of the tumor is required to identify its type.

Surgical removal of the tumor, if possible, is the best treatment. Transitional cell carcinomas are frequently located in critical parts of the bladder or urethra, and removing them requires reconstruction of the lower urinary tract. Survival time tends to be short for these cats, even with surgery, because the tumors spread quickly and often reappear. Chemotherapy and/or radiation therapy may help. You and your veterinarian will want to discuss the treatment options and the quality of life for your cat both during and after treatment.

Problems with urine storage are identified by inappropriate leakage of urine. They can be caused by several different conditions, including failure of the muscles in the bladder to relax appropriately, urethral muscles that do not function properly, birth defects, injury or damage to the urethra or other parts of the urinary system, and overflowing of the bladder.

Urge incontinence occurs when urine leaks during the times when an animal feels the urge to urinate as opposed to urine that leaks when an animal is unaware of it. Urge incontinence is usually caused by irritation of the bladder muscle that forcibly expels the urine. This is usually due to inflammation of the bladder. Weakness of the urethral sphincter (the muscle that opens and closes to allow urine to pass through the urethra) can also cause incontinence. Although it seems contradictory, a cat can also become incontinent if its urethra is partially blocked; the blocked urethra can cause urine to back up and the bladder to overflow.

Incontinence that results from birth defects or malformation of the urinary system usually becomes obvious while the cat is young. For example, a cat that was born with an ectopic ureter on one side might urinate normally but dribble urine on and off, whereas cats with ectopic ureters on both sides are less likely to be able to urinate normally at all.

Problems with urine elimination can have many causes, including physical blockage of the urethra by stones, growths, or scar tissue; a lack of muscle tone in the muscle that expels urine; or problems related to the nervous system. Cats that cannot urinate normally will usually try to urinate often, but the urination will be slow and painful and only a small amount of urine will come out. Cats with urine elimination problems may also develop incontinence over time; if the bladder does not empty properly, it can become stretched out and begin to overflow and leak.

Problems with urination can sometimes be caused by damage or disease that affects the brain or spine, damage to the major nerve in the pelvis that connects to the bladder, a lack of muscle tone in the muscle that expels urine, or excessive muscle tone in the muscle that allows urine to pass through the urethra. Dysautonomia is a condition in cats in which the nervous system does not work properly. It affects multiple body systems and can also lead to urinary incontinence. Cats with any neurologic urination problem may develop incontinence over time if the bladder becomes too full and begins to overflow and then leak.

Also see Dysautonomia in Cats

A thorough physical examination and a history of the cat’s behavior can help your veterinarian determine whether your cat has problems related to urination. Your veterinarian will probably also want to watch your pet urinate. Specialized tests, such as ultrasonography, x-rays, cystoscopy (visualizing the inside of the urethra and bladder with a camera), or neurologic tests, may be helpful in some cases.

Treatment of urination problems will vary depending on the cause. Urethral incontinence can be treated with medication that targets the membrane inside the urethra (called alpha-adrenergic agonist drugs). Urge incontinence can be treated with medication that targets certain nerves (called anticholinergic drugs). Weakened bladder muscles can be treated with medications that target slack muscles (called cholinergic drugs). Additional medications may also be useful in cases where muscle coordination issues are identified.

Complete physical blockage of the urethra is a medical emergency. The treatment varies, depending on the circumstances. A catheter may be used to push the blockage backwards out of the urethra and into the bladder. The blockage may have to be removed during surgery. Cats with bladder muscles that have been weakened by overfill and stretching may require a special catheter that remains in place, or is placed at regular intervals every few hours, for 3 to 7 days. This allows the bladder to empty properly and regain muscle tone.

In cats in which the bladder has lost its muscle tone due to neurologic problems, there are few medical options to restore muscle tone. It is usually necessary for owners to empty the bladder several times a day for the rest of the animal’s life. In these cases, you will need to be trained to express the bladder with your hands.

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