Nephrolithiasis in Cats
Cats that develop clusters of crystals or stones -- known as nephroliths or, more commonly, “kidney stones” -- in the kidneys or urinary tract are said to be suffering from a condition called nephrolithiasis. The kidney is composed of thousands of nephrons, each consisting of blood capillaries and a series of tubes through which filtered fluid flows as urine is produced. The tubes of the nephron drain into ducts through which urine flows; these ducts eventually enter the renal pelvis and a tube through which urine follows into the ureter. Kidney stones or kidney stone fragments can also pass through this system of tubes and into the ureter, causing serious complications.
Both dogs and cats are susceptible to kidney stones. However, some breeds of cat are more susceptible to certain types of kidney stones than others, including the domestic shorthair and longhair, Persians, and Siamese.
Symptoms and Types
Many cats with kidney stones have no apparent signs; that is, the nephroliths are often not detected until diagnostic testing is done for other medical problems. Some symptoms that may occur include blood in urine (hematuria), vomiting, recurrent urinary tract infections, painful difficult urination (dysuria), and frequent urination with small volume of production (polyuria). Other symptoms may appear but vary depending on the location and type of the stones.
Note that some nephroliths may be “inactive”; meaning, they are not infected, not progressively enlarging, and not causing obstruction or clinical signs. Inactive kidney stones may not require removal, but should be monitored periodically (via urine analysis for example) for any changes.
There are a number of causes and risk factors that may contribute to the development of nephrolithiasis and the development of uroliths, such as the oversaturation of stone-forming material's in the cat's urine. Other potential causes include increased levels of calcium in the urine and blood, diets that produce high (alkaline) urine pH, and recurrent urinary tract infections.
You will need to give your veterinarian a thorough history of the cat’s health, including the onset and nature of the symptoms. He or she will then perform a complete physical examination, ultrasound imaging, and urinalysis. However, in order to confirm the diagnosis, identify the mineral content of the stones, and develop a proper course of treatment, pieces of nephroliths must be retrieved for analysis. This is usually achieved by performing a procedure known as extracorporeal shock wave lithotripsy (ESWL), in which stones are broken up within the urinary tract using sound waves.
Many cats diagnosed with inactive kidney stones can be treated at home with proper medication administered in order to dissolve the stones. An adjustment to the cat's diet is also necessary. These dietary changes will be dependent on the chemical makeup of the kidney stone.
In severe cases, the cat may require immediate removal of the kidney stone(s) and hospitalization. There are a number of options for kidney stone removal, including surgery or ESWL.
Living and Management
Because kidney stones tend to recur, routine monitoring is essential. Most veterinarians recommend abdominal X-rays and/or ultrasound examinations every three to six months post initial treatment. A periodic urine analysis is also frequently recommended.
If your cat is predisposed to nephrolithiasis, special foods and dietary management can be effective at preventing stone formation.