Paula Steele, DVM

Miniature Schnauzers are one of the breeds considered to be at increased risk of bladder stones. These calculi are macroscopic concretions in the urine and can be found anywhere in the urinary tract but are most commonly found in the bladder. There are several different types of calculi with struvite and oxylate the most common in our breed.

Multiple factors are involved in the formation of stones:

1) supersaturation of the urine with minerals, due to:

- increased amounts of mineral in the urine
- urine pH which allows the minerals to precipitate out
- other factors which cause crystallization-such as high Calcium levels in the blood

2) upper urinary tract infection (UTI)

3) some types of calculi occur secondarily to other metabolic problems.

Signs of bladder stones: straining to urinate, blood in urine, increased frequency of urinating and the urine maybe cloudy and foul smelling. Sometimes small stones are even passed. Diagnosis is usually made by palpation of the stones, radiographs and/or ultrasound.

Struvite stones most commonly are associated with urinary tract infections and usually occur in an alkaline pH. It is suspected that susceptible Minis inherit an abnormality of host defenses of the urinary tract which make them more susceptible to infection. These stones are more common in females than males. Risk factors are glucocorticoid exposure which predisposes to UTI, abnormal retention of urine and alkaline urine.

Oxylate stones are formed in an acid pH and are more common in males than females. They are often associated with an elevated Calcium level in the blood. Risk factors for Calcium Oxylate stones—Calcium supplements independent of meals, excessive dietary protein, sodium or vitamin D, additional dietary oxylate (chocolate and peanuts), exposure to high levels of glucocorticoids, diets that promote an acidic urine and furosemide, and deficiency of vitamin B6. Some Veterinarians feel that these stones are associated with feeding Commercial dog food.

Ammonium urate stones are found in dogs with liver disease and portalsystemic shunts.

Treatment of urinary calculi consists of either medical dissolution or surgical removal. Because the chemical composition of the calculi determines what treatment will be effective, it is very important to determine what the chemical composition of the calculi is as some types will not respond to medical dissolution.

Medical dissolution consists of creating a dilute urine, altering the pH, decreasing the excretion of the type of minerals causing the calculi and controlling infections. Medical treatment continues for one month after the calculi are dissolved. Surgical treatment consists of entering the bladder and removing the calculi and is indicated when the type of calculi doesn’t respond to medical treatment or when the dogs condition requires rapid resolution of the problem.

Prevention of recurrence is of utmost importance as calculi will reoccur in up to 47% of these dogs if long term changes are not made. Recurrence can be reduced by eliminating the predisposing factors. In struvite calculi, eliminating or controlling infection is essential. This should be done with a culture and sensitivity of the urine to determine what bacteria is present and often requires long-term antibiotic treatment of at least 4-6 weeks. Periodic monitoring of a morning urine pH can help detect the possibility of an early infection. Maintaining an acidic pH, dilute urine and low urine magnesium will help prevent recurrence. With calcium oxylate calculi, sodium and ascorbic acid (vitamin C) supplementation should be avoided. Restricting sodium and alkalinization of the urine will help prevent recurrence.

Bibliography:
1) The 5-Minute Veterinary Consult by Larry P Tilley and Francis W.K. Smith ,Jr.
2) Saunders Manual of Small Animal Practice

Added December 8, 2005