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Nephrolithiasis is the medical term for the condition in which clusters of crystals or stones -- known as nephroliths or, more commonly, “kidney stones” -- develop in the kidneys or urinary tract. 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 dog are more susceptible to certain types of kidney stones than others. For example, kidney stones containing calcium and oxalic acid (known as calcium oxalate nephroliths) are more likely to be found in Lhasa Apsos, Yorkshire Terriers, and Miniature Poodles. Kidney stones containing uric acid (known as urate nephroliths), on the other hand, typically affect Dalmatians, Yorkshire Terriers, and English Bulldogs.
Symptoms and Types
Many dogs 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 dog'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 dog’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.