Uroliths (Sand, Stones, Calculi) and Urolithiasis in Guinea Pigs

Small Mammals

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Uroliths, or stones, are accumulations of crystallized minerals that form in the urinary tract. Urolithiasis is the disease that occurs because of the formation of uroliths in the urinary tract.

Uroliths can be found in the kidneys, ureter (the tube that leads from the kidney to the bladder), bladder or urethra (opening from the bladder to the exterior of the body). Uroliths form when conditions in the urinary tract cause the minerals in the urine to solidify and form concretions of sand, stones or calculi.

What to Watch For

  • Straining to urinate
  • Blood in the urine
  • Urine dribbling
  • Malodorous urine
  • Wet fur around the rear end and back legs
  • Swollen abdomen
  • Painful abdomen
  • Hunched stance with the back arched
  • Excessive grooming of the area around the rear
  • Depression
  • Loss or appetite
  • Weight loss
  • Unsuccessful attempts to urinate

    If these changes are noted, seek veterinary care immediately. Many guinea pigs with uroliths may appear normal.

    Diagnosis

  • History, particularly of the diet, and physical examination
  • Complete blood count
  • Blood chemistries
  • Urinalysis
  • Cytology (microscopic evaluation of urine)
  • Culture of urine and antimicrobial sensitivity testing
  • Radiographs (X-rays)
  • Ultrasound

    Treatment

  • Placement of a catheter through the urethra
  • Surgical removal of the uroliths
  • Systemic antibiotics
  • Fluids and supportive nutrition

    Home Care and Prevention

    On a daily basis, monitor fecal and urine output to assure proper food and water consumption and digestion. Monitor weight daily.

    If surgery was performed, monitor and/or treat incision line as directed by your veterinarian.

    Make sure your guinea pig always has a plentiful supply of clean fresh water. Feed fresh pelleted foods specifically designed for guinea pigs

  • Uroliths form when minerals normally found in the urine crystallize and combine with sticky proteinaceous materials (referred to as an organic matrix) to form masses. These concretions can be singular or multiple and large (referred to as stones) or small and immense in number (referred to as sand). The disease that is associated with the formation of uroliths is referred to as urolithiasis.

    Uroliths usually form in the bladder but some originate in the kidneys and then pass down the ureter and into the bladder where they can enlarge. While uroliths usually form in the bladder or kidney, they may be found at any location in the urinary tract. In some cases, guinea pigs with uroliths have concurrent bacterial infections while in others, uroliths occur in the absence of a detectable bacterial infection. The clinical changes that might occur depend on the size and location of the urolith and whether or not a bacterial infection is occurring.

    Some guinea pigs with uroliths may be clinically normal with no recognizable changes in attitude or blood values. If a urolith is causing damage of the lining of the urinary tract or if a bacterial infection is present, then the guinea pig may be feverish, depressed and have an elevated white blood cell count. These clinical changes are similar to those associated with many bacterial, fungal or viral infections. Clinical changes from uroliths that restrict urine from properly entering or exiting the bladder include frequent urination, blood in the urine, urine dribbling, wet fur in the rear end and legs and urine dribbling. All of these clinical changes warrant immediate veterinary attention.

    Inability to pass urine rapidly leads to coma and death and should be treated as an emergency. Seek veterinary care immediately if a guinea pig strains or vocalizes while trying to urinate, or if a normal amount of urine is not noted.

    Other problems with the urinary tract that may cause similar clinical changes include cancer, abscesses and infections. In older males (called boars), accumulations of ejaculate can cause obstruction of the urethra causing clinical changes similar to those noted with uroliths.

    The exact factors that determine which guinea pigs will or will not develop uroliths remain undetermined. In other species, a genetic predisposition, metabolic disorders, improper nutrition, inadequate water intake, obesity and bacterial infections have all been suggested to precipitate the formation of uroliths. Female guinea pigs older than three years are particularly likely to have inflammation of the bladder (called cystitis) and urolithiasis. Diabetes mellitus and the anatomy of the guinea pig urinary tract are also considered factors in the development of urolithiasis.

    Most uroliths in guinea pigs are comprised of calcium carbonate and occasionally magnesium and ammonium. It is theorized that the formation of uroliths may predispose a guinea pig to bacterial infections of the urinary tract or conversely, bacterial infections of the urinary tract may precipitate formation of uroliths. Calcium oxalate uroliths have been reported in guinea pigs with bladder infections associated with Streptococcus sp. E. coli and Staphylococcus sp. infections have also been reported in guinea pigs with urolithiasis.

    Diagnosis

    Your veterinarian may use radiographs (X-rays) or changes in the types of blood cells (CBC) or enzymes found in the blood (blood chemistry) to evaluate the overall health status of a sick guinea pig.

  • Radiographs. The most common radiographic change associated with uroliths is the presence of a mineral density in the urinary tract. Uroliths may be easy to visualize radiographically when located in the kidney or bladder but may be difficult to visualize in the urethra. Ultrasound may be used to document the presence of uroliths that are radiolucent or otherwise difficult to visualize radiographically.

  • Blood work. Blood tests may be normal in guinea pigs with uroliths if the mass has caused minimal irritation of the urinary tract, minimum blockage of urine flow and is not associated with a bacterial infection. If the lining of the urinary tract is damaged or a bacterial infection is present, then the white blood cell count may be elevated (neutrophilia). In guinea pigs with advanced bacterial infections that have passed into the blood stream (called sepsis), the white blood cell may be decreased (neutropenia) with a high proportion of immature cells and/or toxic changes. This finding is associated with a poorer prognosis.

  • Urinalysis. Visual and chemical analysis of the urine may help determine the type or uroliths that are present and whether or not a bacterial infection is occurring. Culture is usually necessary to specifically identify the type of bacteria that may be present. Cytology (microscopic evaluation of cells) is important in helping to identify the presence of organisms that may be difficult to grow in the laboratory.

    Therapy in-depth

    Treatment of urolithiasis requires removal of existing uroliths, control of primary or secondary bacterial infections and initiating the necessary changes to prevent recurrence. The precise treatment used by your veterinarian will depend on whether or not your guinea pig is able to urinate and on the type, number and location of the uroliths.

  • If your guinea pig is unable to produce urine, your veterinarian will first pass a catheter through the urethra to the bladder. If this does not allow for normal passage of urine, then emergency surgery will be necessary.

  • If your guinea pig is able to pass urine, then your veterinarian may stabilize your pet with fluids and antibiotics (if a urinary tract infection is present) before surgically removing any uroliths.

  • Uroliths may recur even in properly treated guinea pigs and effective preventative measures have not been reported.

  • Agents that are used to acidify the urine and reduce the formation of some types of uroliths in other species are not recommended in guinea pigs because their kidneys inefficiently excrete acids.

  • Your veterinarian is likely to send any urolith removed from your guinea pig to a lab for a compositional analysis. This information can be crucial to implementing changes that will prevent urolithiasis from recurring.

    Follow-up Care

    Optimal treatment for your guinea pig requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your guinea pig does not rapidly improve.

  • Make certain you administer all prescribed medications at the appropriate times. Contact your veterinarian immediately if you have difficulty treating your guinea pig as prescribed. If you are having problems, it may be best to hospitalize him to assure that a proper course of treatment is administered.
  • Some blood may be noted in the urine for a day or two after surgery, palpation or catheterization of the bladder.

  • Urine output should be carefully monitored several times a day in guinea pigs that are being treated for urolithiasis.

  • If surgery was performed, check the incision line several times a day (or as directed by your veterinarian) for swelling, discharge or redness. If any of these changes are noted, contact your veterinarian immediately. Use only clean shredded paper as cage bedding. Your veterinarian may recommend hot packing or application of antimicrobial agents to the incision.

  • Your veterinarian may recommend radiographs, ultrasound, microscopic evaluation of urine and culture of the urine several weeks after completing the recommended therapy for urolithiasis. Uroliths frequently recur in guinea pigs and effective preventative measures have not been reported. Thus, your veterinarian may recommend these same procedures at regular intervals for the remainder of your guinea pig's life to monitor the health of the urinary tract.

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