Kidney stones in dogs: diagnosis and management
Introduction
For a long time, uroliths affecting the upper urinary tract were considered extremely rare in dogs; however, the increasing availability of diagnostic imaging techniques in routine clinical practice has shown that kidney stones in dogs are more common than previously believed.
In many cases, patients with kidney stones may not manifest any clinical signs for years. However, when they do, they are usually severe (impaired kidney function, pyelonephritis, hydronephrosis) and often require a specialised intervention. Which is why vets must be familiar with the diagnosis and management of this type of urinary stone.
Diagnosis
Initially, the presence of kidney stones in dogs is established based on findings of imaging tests (X-ray, ultrasound or CT) performed on patients with a clinical suspicion of lithiasis or as an incidental finding in dogs undergoing the tests for other reasons. Whenever a kidney or ureteral stone is detected, the diagnostic assessment should include a blood count, blood chemistry and complete urinalysis (pyelocentesis in certain cases). The patient’s signalment and information from these tests can be used to try to predict the stone’s composition and select the best treatment option.
Image taken from the webinar “Urolithiasis in cats and medical management of ureteral obstructions” by Luis Feo
Luis Feo
Although it has been reported that 20–60% of kidney stones in dogs are struvite stones, nowadays most authors agree that at least 60% of kidney and ureteral stones in dogs are composed of calcium oxalate.1-3 This means they will be radiologically detectable, although it may be difficult to identify small stones on plain X-rays and more advanced diagnostic techniques may be required.
Urate and cystine stones (much less common) are barely radiopaque or radiolucent, so they cannot be detected on X-rays and other diagnostic techniques must be used in case of clinical suspicion.
STONES AND pH
Struvite kidney stones in dogs mainly affect females and are almost always secondary to a urinary infection. They usually occur because the urine has an alkaline pH. However, urate and calcium oxalate crystals precipitate at pH < 7.
Cystine precipitates at more variable pHs.
UROLITHIASIS AND BREED PREDISPOSITION
Certain breeds are predisposed to specific types of kidney stones, such as:
- Urate stones in Dalmatian, Bulldog and dogs with a portosystemic shunt;
- Cystine in Bulldog, Newfoundland, Labrador or entire males;
- Calcium oxalate in the Miniature Schnauzer, Terrier, Poodle or Shih Tzu.1
Kidney stones in dogs: treatment
The treatment of kidney stones in dogs should be assessed individually.
- In asymptomatic patients, the recommendation is to monitor the development of stone size and kidney function before deciding whether it needs to be removed.1-5
- On the other hand, the medical management of kidney stones in dogs is indicated in all cases where the type of stone or clinical suspicion indicate that dissolution is possible, provided that the right conditions exist (i.e., the stone can be surrounded by urine and there is no obstruction or uncontrollable urinary tract infection).
- Medical dissolution is contraindicated if there is ureteral obstruction, unless a stent or subcutaneous bypass device can be placed to maintain urine flow while the stone is being dissolved.
MEDICAL TREATMENT
- The medical treatment of struvite kidney stones is based on antibiotic therapy until the stone is completely dissolved together with a low phosphorus and magnesium diet that promotes urine acidification.1,5
- Urate uroliths are considered suitable for medical dissolution (low purine diet to alkalinise the urine and allopurinol 15 mg/kg/12 hours), even though an efficacy of only 30–40% has been reported.
- Medical treatment is not recommended in dogs with underlying liver disease.1,5
- Finally, the treatment of cystine stones includes a diet low in amino acids and cystine that promotes an alkaline pH, the use of tiopronin (20 mg/kg/12 hours) and, if necessary, potassium citrate as an alkalising agent.1
ELIMINATION OF KIDNEY STONES
Elimination is indicated in certain cases:
- Progressive loss of renal parenchyma secondary to the kidney stone’s increasing size.
- Pyelonephritis refractory to medical management.
- Obstruction that could cause hydronephrosis.1
The current recommendation is to use the least invasive technique possible. This means that traditional techniques (nephrotomy, pyelotomy and ureteronephrectomy) are becoming less popular because of their high morbidity and mortality compared with minimally invasive procedures, with current leading recommendations being extracorporeal lithotripsy (with ureteral stent placement if there is a risk of ureteral obstruction) and endoscopic percutaneous or surgically assisted nephrolithotomy.1,5
Conclusions
We now know that kidney stones in dogs are much more common than we used to think 15–20 years ago. Although many patients with kidney stones may not present any clinical signs, it is essential to monitor the stone’s development correctly, check its potential effects on renal function and assess the possibility of medical dissolution. Furthermore, imaging tests should be included when monitoring patients who may be considered at risk, such as dogs with leishmaniasis under treatment with allopurinol or those with chronic kidney disease.
