Introduction

• Urolithiasis refers to the presence of stones anywhere in the urinary tract.
• Most canine uroliths are found in the lower urinary tract.
• Most common types: struvite (magnesium ammonium phosphate), calcium oxalate, cystine and ammonium urate.
• Rarer types: calcium phosphate, silica, carbonate, xanthine and drugs or their metabolites.
• Incidence estimated at 0.3-2.8%.
• Cause: (and therefore treatment) depends on type of urolith; usually due to underlying inherited, congenital or acquired metabolic disorder or infection.
• Signs: usually of lower urinary tract disease (may be none).
• Prognosis: many uroliths recur unless underlying cause is corrected, eg infection.
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Pathogenesis

Etiology

• Supersaturation of urine with crystalloid → crystal nidus (nucleus) formation.

Predisposing factors

• Urine pH.
• Diet.

• Metabolic acidosis or alkalosis Acid base imbalance.
• Medication.
• Anatomical abnormalities.
• Lifestyle.

• Gender.
• Sedentary lifestyle.

Specific

• Urinary tract infection Cystitis (struvite).
• Portosystemic shunt Congenital portosystemic shunt (CPSS) (urate).

• Hyperparathyroidism Renal secondary hyperparathyroidism Nutritional secondary hyperparathyroidism (calcium oxalate).
• Intestinal hyperabsorption of calcium (calcium oxalate).

• Breed.

Pathophysiology

• Inherited, congenital or acquired predisposing condition; depends on nature of urolith.
• Supersaturation of urine with calculogenic crystalloids.

• Approximately 50% of uroliths  .     .
• Oversaturation of urine with magnesium ammonium phosphate.
• Urinary tract infection with urease-synthesizing bacteria → hydrolysis of urea → ammonia and carbon dioxide → alkaline urine.
• Other factors: alkaline urine, high protein diet, genetic predisposition.

• Approximately 30% of uroliths   .
• Hypercalciuria and/or hyperoxaluria.
• Causes of hypercalciuria:
  • Intestinal hyperabsorption of calcium.
  • Decreased renal absorption.
  • Hypercalcemia Hypercalcemia: overview , eg hyperparathyroidism, paraneoplastic.
  
  Cystine
• Approximately 1% of uroliths   .
• Metabolic defect → increased urinary excretion of cystine, lysine, arginine and ornithine.
• Acidic urine → precipitation of cystine.
  Urate
• Approximately 8% of uroliths   .
• Dalmatian → defect in hepatic uric acid metabolism → increased urinary urate excretion.
• Other breeds: hepatic dysfunction or portal vessel anomalies → decreased urate metabolism.

Timecourse

• Uroliths may not be detected until dog is middle-aged.

Diagnosis

Treatment

Prevention

Outcomes