Urolithiasis in Small Mammals
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. They are most commonly found in rabbits and ferrets but can also affect smaller animals.
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
- Differences in dietary composition and water intake
- Underlying metabolic diseases
- Bacterial infections of the urinary tract
The cause for stone formation is unknown in many cases.
The various types of calculi are named according their predominant mineral composition. 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
Diagnostic tests are needed to identify urolithiasis as the cause of your pet's symptoms and to exclude other disease processes.
A complete medical history and physical examination, including palpation of the abdomen, is essential in all sick animals. For many small mammals, a physical exam may be all that is necessary to suspect bladder stones. If possible, additional tests will help confirm the diagnosis, such as:
- 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
In a few cases, additional tests may be recommended for ferrets and rabbits. These are rarely, if ever, performed on most small mammals:
- 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. For rabbits and ferrets, more aggressive treatment is possible. Due to size and cost concerns, surgery is often not performed in rodents:
- 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.
Home Care and Prevention
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.
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.