Nephrolithiasis (Kidney Stones) in Cats

Overview of Kidney Stones in Cats

Nephrolithiasis is the condition marked by the presence of renal calculi or kidney stones. One function of the urinary system is the removal of body wastes in liquid form. Some mineral wastes are only slightly soluble and may form crystals. If the transit time of crystal movement through the urinary system is prolonged, crystals may interact and grow into stones.

Causes of Kidney Stones in Cats

Several types of stones can affect cats and dogs. Each type of stone is often associated with its own specific cause. General causes include:

• Underlying urinary tract infections or infection within the kidney
• Genetic defects
• Dietary factors or supplements
• Administration of certain medications
• Concurrent or underlying conditions or illness

Overall, nephroliths are slightly more common in the male cat and are generally seen in the middle-aged animal, although can be seen in any age. There are different breed predilections for each type of calculi. In cats, nephroliths are seen most commonly in the domestic shorthair.

Urine retention and the formation of concentrated urine may predispose to calculi.

What to Watch For

• Bloody urination
• Abdominal pain
• Recurrent urinary tract infections
• Vomiting

Clinical signs depend on the exact location, size, shape and number of kidney stones. Affected individuals may have no clinical signs. Other signs such as painful urination or frequent urination may be seen in patients who have a concurrent lower urinary tract infection. Some patients may be extremely ill if they have associated kidney failure or severe infection.

Diagnosis of Nephrolithiasis (Kidney Stones) in Cats

• Complete blood count (CBC)
• Biochemical profile
• Urinalysis
• Bacterial urine culture
• Radiographs (X-rays)
• Abdominal ultrasound or excretory urography

Treatment of Nephrolithiasis (Kidney Stones) in Cats

• Depending on the patient, recommended treatment options may vary.
• Inactive nephroliths may only require periodic monitoring.
• If the stones are an incidental finding or the pet is not having severe clinical signs, medical and/or dietary dissolution may be attempted. It is important for both you and your veterinarian to monitor your pet very closely during this period, as it is possible that not all stones can or will dissolve.
• If the patient is in kidney failure or is having severe clinical signs associated with the presence of the stones, their removal, either surgical or by lithotripsy, would be recommended.
• Antibiotic therapy is indicated in those patients with concurrent urinary tract infections.
• Fluid therapy is indicated in those patients who are dehydrated, have severe infections, or have concurrent kidney failure.

Home Care

If your pet is on a stone dissolving diet, complete compliance is necessary. NO snacks or other diets are permitted, as these may negate the beneficial effects of the special diet. Administer all medication and return for follow-up as directed by your veterinarian.

If your pet is being treated for nephrolithiasis and suddenly seems ill, contact your veterinarian at once.

Preventative Care

Eliminating urinary tract infections may help prevent nephrolithiasis. Treating and controlling underlying disorders may help prevent recurrence of stones.

In-depth Information on Feline Nephrolithiasis

Nephrolithiasis is the condition characterized by the presence of nephroliths (also referred to as calculi or kidney stones) which are stones located within the kidney pelvis. Nephroliths have several potential causes, and a host of possible presentations are associated with their presence. Some factors may enhance the susceptibility to nephrolithiasis such as congenital abnormalities, metabolic disorders or disorders that promote urine retention, but no specific underlying disorder need exist.

Individuals with kidney stones may be have no clinical signs, although some patients may be quite ill, as the presence of stones can cause pain and lead to kidney failure, sepsis (infection throughout the bloodstream) and even death. Depending on the specific case, specific diagnostics and therapeutics are tailored to the individual.

Several diseases/disorders are similar to nephrolithiasis. These include:

• Pyelonephritis, which is an infection of the kidney
• Urolithiasis, which are stones anywhere throughout the urinary tract
• Lower urinary tract infection
• Chronic kidney failure may be associated with or the result of nephrolithiasis.
• Other causes of abdominal pain such as pancreatitis or peritonitis (inflammation of the abdominal cavity) need to be considered, as some animals with nephrolithiasis will experience abdominal pain.
• Disorders associated with back pain such as intervertebral disc protrusion or a spinal infection or tumor may need to be differentiated.
• Disorders that cause increased thirst and urination including hyperadrenocorticism (Cushing’s disease), diabetes mellitus, kidney disease and liver disease

Diagnosis In-depth

Certain diagnostic tests must be performed to diagnose nephrolithiasis and exclude other disease processes that may cause similar symptoms. A complete history, description of clinical signs, and thorough physical examination are all an important part of obtaining a diagnosis of nephrolithiasis. In addition, the following tests are recommended:

• A complete blood count (CBC) may be within normal limits, although an elevated white blood cell count may be present, especially in those patients with associated pyelonephritis.
• A biochemical profile may be within normal limits, but may reveal elevations in kidney enzymes or electrolyte abnormalities.
• A urinalysis may reveal blood, white blood cells, protein, bacteria, crystals and/or white blood cell casts. The absence of any or all of these does not rule out nephrolithiasis.
• A bacterial urine culture is performed to assess for the presence of a urinary tract infection, but may be negative in some cases.
• Abdominal X-rays are often diagnostic for certain types of radiopaque stones that are clearly seen on X-rays. If they are within normal limits, that does not rule out the possibility of nephroliths.
• Abdominal ultrasound is helpful in evaluating the kidney and confirming the presence, size, and number of nephroliths, in addition to assessing the rest of the urinary tract for stones. Additionally, characteristic changes are seen within the renal pelvis (inside of the kidney) that may be consistent with kidney infection. Ultrasound is a noninvasive procedure that often necessitates the expertise of a specialist and/or referral hospital.

Your veterinarian may recommend additional tests to exclude or diagnose concurrent conditions. These tests are not necessary in every case, but may be of benefit in certain individuals and are selected on a case-by-case basis. These include:

• Excretory urography is an intravenous dye study that “lights up” the upper urinary tract (kidneys and ureters). It is very helpful in documenting stones in these structures, and may identify other abnormalities, such as pyelonephritis or ectopic ureters. Ectopic ureters are a congenital abnormality in which the ureter or tube that drains the kidney into the bladder joins the bladder in an abnormal position.
• A bacterial culture of the kidney pelvis may be obtained with the guidance of abdominal ultrasound. This may be particularly important in the patient who has a negative urine culture obtained from the bladder.
• If a stone or fragment of stone is available after it has passed into the lower urinary tract or even outside the body, because of natural circumstances or due to the intervention of extracorporeal shockwave lithotripsy (ESWL), it should be submitted for stone analysis. Stone identification may be of benefit in the treatment and prevention in the future.

Therapy In-depth

Animals with inactive nephroliths that are not causing any clinical signs may not require therapy. They should be monitored periodically by urinalysis, urine culture, radiographs and/or ultrasound. Although some inactive stones may remain inactive for the duration of the individual’s life, it is important to note that inactive stones may become active, causing severe clinical signs with very little warning. Equally important is choosing the most appropriate therapy for the patient who is having associated clinical signs. All recommendations by your veterinarian should be followed very closely, and any questions or concerns that arise during the treatment protocol should be addressed immediately.

• Medical and/or dietary dissolution may be attempted. It is important for both you and your veterinarian to monitor your pet very closely during this period, as it is possible that not all stones can or will dissolve. The specific medication and/or diet will vary depending on the type of stone. As some stones are not available for analysis, it can be a guessing game, taking into account the size, shape, and visibility of the stones through the diagnostic work up.
• If the patient is in kidney failure or is having severe clinical signs associated with the presence of the stones, their prompt removal is recommended.
• Surgical removal necessitates a nephrotomy, or cutting into the kidney, to retrieve the stone. There are cases that might necessitate a nephrectomy, which is kidney removal. These are procedures that are associated with risk, and it is recommended that they be performed by an experienced individual.
• Extracorporeal shock wave lithotripsy (ESWL) is a relatively safe and effective way of treating nephroliths in dogs, but it can only be performed at certain referral institutions. In this procedure, the stones are crushed in the bladder with shock waves and then the fragments are flushed out.
• Antibiotic therapy is indicated in those patients with urinary tract infections.
• Fluid therapy is indicated in those patients that are dehydrated, have severe infections or kidney failure.

Follow-up Care for Cats with Kidney Stones

If your pet is on a stone-dissolving diet, complete compliance is necessary. NO snacks or other diets are permitted, as they may negate the beneficial effects of the special diet. Administer all medication and return for follow-up as directed by your veterinarian.

The expected course and prognosis is highly variable, depending on the type, location, and size of stone, and the presence of secondary complications. If your pet is being treated for nephrolithiasis, and suddenly seems ill, contact your veterinarian at once.

Eliminating urinary tract infections may help prevent nephrolithiasis. Treating and controlling underlying disorders may help prevent recurrence of stones. Dietary modification is recommended in animals with a history of stones anywhere in the urinary system to help prevent recurrence.

Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your pet does not rapidly improve.

General blood work may need to be reevaluated as recommended by your veterinarian. Abdominal X-rays or ultrasound (depending on the stone type) should be checked every several months at first, and 1 to 2 times yearly thereafter. Urinalysis and urine culture should be checked as well.