Urolithiasis refers to the formation of stones (calculi or uroliths) in the urinary tract. Calculi can be found anywhere in the urinary tract, in the kidneys, the ureter or the bladder, but are most common in the bladder.
Calculi form due to oversaturation of the urine with certain minerals. Several factors may contribute to this oversaturation including increased concentrations of specific minerals in the urine, alterations in the pH (acidity or alkalinity), highly concentrated urine, presence or absence of stimulators, and inhibitors of crystal formation.
Several factors can contribute to development of urolithiasis. These include: Genetic factors like the altered urate metabolism in Dalmatians
Differences in dietary composition and water intake
Underlying metabolic diseases such as high blood calcium concentration arising from overactivity of the parathyroid glands
Congenital problems such as abnormal blood vessel shunting blood around the liver and contributing to urate stone formation
Bacterial infections of the urinary tract (struvite stone formation). The cause for stone formation is unknown in many cases.
The various types of calculi are named according their predominant mineral composition. In cats, calculi composed of the minerals magnesium ammonium phosphate (commonly called struvite) and calcium oxalate are most common. Urate calculi occur less commonly. Cystine and silica calculi are relatively rare. The different types of calculi must be treated differently. Consequently, it is important for your veterinarian to be able to obtain calculi for chemical analysis.
The risk of recurrence for urolithiasis is high and ranges from 20 to 50 percent. The pet's symptoms depend upon the number of stones, their location in the urinary tract, the physical characteristics of the stones (smooth or jagged), and the presence of bacterial urinary tract infection.
What to Watch For
Difficult or frequent urination
Urinating in inappropriate locations
Blood in the urine
Symptoms caused by kidney stones include back or abdominal pain or occasionally abnormal odor to the urine if bacterial infection is present. Surprisingly, however, many pets with kidney stones have few or no symptoms.
Diagnostic tests are needed to identify urolithiasis as the cause of your pet's symptoms and to exclude other disease processes. Your veterinarian may recommend:
Complete medical history and physical examination, including palpation of the abdomen. Bladder stones can be difficult to palpate due to the tendency of many pets to tense their abdomen when the veterinarian attempts to palpate them. The medical history may include questions about the pet's urine stream, the frequency of urination, presence of blood in the urine, change in water consumption, changes in appetite, weight loss and history of previous illness or infection.
Urinalysis to evaluate urine concentration, acidity or alkalinity (called pH), presence of red blood cells, white blood cells, bacteria and crystals
Abdominal X-rays to identify stones that are dense enough to be visualized
Other diagnostic tests that may be completed include:
Urine culture and sensitivity to identify bacterial urinary tract infection
Serum biochemistry tests to assess kidney function
Complete blood count to evaluate for infection
Abdominal ultrasound to evaluate for obstruction of the urinary tract by stones
Contrast dye X-ray studies to visualize some stones not visualized on plain X-rays
Stone analysis to identify the mineral composition of the stones and guide your veterinarian in treating urolithiasis
Treatments for urolithiasis may include one or more of the following:
Treatment of bacterial urinary tract infection with antibiotics
Removal of stones surgically or by dietary intervention. There are advantages and disadvantages to both methods. Surgery is invasive but usually insures removal of all stones and allows for mineral analysis of the stones. Dissolution of stones by dietary methods is not invasive but does not allow mineral analysis of the stones and requires your veterinarian to make an educated guess about the type of stone present. Some stones can be dissolved by dietary means and others cannot. Whether or not to attempt dietary dissolution will depend on your pet's general health, the type of stone suspected, the location and number of stones and other factors that your veterinarian will discuss with you. In many instances, surgery is the most direct way to remove stones and submit them for analysis.
At home, be sure to administer any medications prescribed by your veterinarian. Give antibiotics according to the schedule prescribed. It's important to allow your pet free access to fresh clean water.
Follow-up with your veterinarian for physical examinations and urinalysis as directed. Urine culture should be repeated 5 to 7 days after completion of antibiotic treatment to ensure eradication of infection. If your pet has a poor response to treatment, further workup may be required to search for underlying disease processes.
Stone analysis will guide your veterinarian's treatment plan:
Struvite stones: antibiotics to treat bacterial infection
Oxalate stones: thiazide diuretics and potassium citrate
Urate stones: allopurinol
Cystine stones: penicillamine or 2-mercaptopropionyl glycine (2-MPG or Thiola)
Most stones are difficult to prevent. Providing your pet with frequent opportunities to urinate and an ample supply of fresh clean water may help.
Prompt treatment of urinary tract infections can help reduce the potential for certain stone formation.