What is calcium oxalate urolithiasis?
Calcium oxalate urolithiasis is the formation of calcium oxalate stones (called uroliths or calculi) within the urinary tract. Calcium oxalate is a common mineral compound and occurs in the urine as crystals. Calcium oxalate stones account for 30% to 50% of all stones removed from dogs and cats.
What causes calcium oxalate urolithiasis?
Calcium oxalate stones are caused by excessive calcium and/or oxalate in the urine or by a lack of citrate in the urine. Urine citrate is an inhibitor of calcium oxalate stone formation. Diets high in calcium, protein, salt, and vitamin D can cause excessive amounts of calcium in the urine. Foods containing oxalate (such as chocolate [see note] or peanuts) can increase urinary oxalate. In humans, vitamin B deficiency and fat malabsorption are associated with calcium oxalate stones. Some medications, such as diuretics and steroids, can promote large amounts of calcium in the urine.
Note: dogs and cats should not eat chocolate due to its potential toxicity. Eating chocolate can cause gastrointestinal upset, nervous system disease, and heart disease. These affects are due to the theobromine and caffeine in the chocolate and not to the oxalate.
What are the signs of calcium oxalate urolithiasis?
The signs of calcium oxalate urolithiasis depend on the location, size, and number of stones. Some animals may have calcium oxalate stones with no signs of disease. Typical signs are blood in the urine; frequent urination; and difficulty urinating, especially if a stone has blocked the urethra (the tube leading from the bladder to outside the body).
How is calcium oxalate urolithiasis diagnosed?
The diagnosis of calcium oxalate urolithiasis can be challenging, depending on the location and number of stones. The stones may be located in any part of the urinary system, including the kidneys, ureters, bladder, and urethra. The veterinarian will try to detect stones by palpating the abdomen during the physical examination. The bladder may be thick and contracted. The bladder will be enlarged if the pet has complete obstruction of the urethra.
Urinary stones need to be differentiated from other causes of difficulty in urinating, such as urinary tract infection or cancer of the urinary tract. Urinalysis may reveal calcium oxalate crystals. If possible, the actual type of stone needs to be identified by special testing. Stones can be composed of a variety of minerals; not all stones are calcium oxalate. Stones may be obtained for analysis when they pass on their own in the animal's urine or they may be retrieved by different procedures including surgery.
Calcium oxalate stones can be seen on radiographs (X-rays). Imaging studies including contrast radiographs (using dyes) or ultrasound (visualizing deep body structures by recording ultrasonic waves) may be needed to verify obstruction of the ureters (the tubes leading from the kidneys to the bladder).
How is calcium oxalate urolithiasis treated?
The treatment for calcium urolithiasis will be based on the location of the stones and whether or not the stones are causing a blockage of urine flow. If the stones are causing obstruction of urine, they must be removed immediately. The veterinarian can sometimes flush out small stones in the bladder during an office visit. Stones in the kidneys or ureters may be removed by surgery or by non-surgical methods, such as shock wave lithotripsy (crushing the stone using shock waves directed through the abdominal wall). No available drugs or special diets are effective in dissolving calcium oxalate stones.
Calcium oxalate stones often recur; therefore, preventing their formation is the goal. Sometimes a diet low in calcium, oxalate, sodium, and protein helps minimize the formation of stones. The veterinarian may prescribe a specialized diet to attempt to prevent recurrences. Ideally, the diet should contain additional water. Canned food is preferable to dry food because of the extra water. Supplemental vitamins C and D should be avoided.
What is the prognosis for animals with calcium oxalate urolithiasis?
The prognosis (outcome) for animals with calcium oxalate urolithiasis is fair. Calcium oxalate stones often recur in dogs within three years of initial diagnosis. Some dogs will have recurrences more rapidly. Data is not available for the incidence of recurrence in cats.