Introduction

• Cause: feline urolithiasis is the second most frequent cause of 'feline lower urinary tract disease' (FLUTD) Feline lower urinary tract disease (FLUTD) (after feline idiopathic cystitis Idiopathic cystitis).
• Signs: depend on location of urolith but commonly hematuria, dysuria, pollakiuria and/or urethral obstruction. Nephroloths/ureteroliths can cause acute kidney injury (AKI).
• Diagnosis: depend on location: clinical signs, history, palpation, radiography, ultrasonography, urinalysis.
• Treatment: depends on location: surgery, catheterization; medical dissolution poorly evaluated except for struvite uroliths.
• Prognosis: depends on type of urolith and location.
  Print off the owner factsheet on Bladder stones and kidney stones Bladder and kidney stones to give to your client.Use the interactive tools from ROYAL CANIN® UK to explain cat anatomy and disease conditions to your client. Visit ROYAL CANIN Natom Explorer to find out more.

Pathogenesis

Etiology

• Supersaturation of urine with minerals, together with predisposing factors such as urinary tract infection, metabolic disorders or dietary factors.
• Urolith formation is a complex situation involving the genetics of the cat, saturation of the urine and complex promotors and inhibitors.

Predisposing factors

General

• Middle aged cats.
• Obesity Obesity and a sedentary lifestyle are risk factors. May be due to urinary retention (as a result of 'couch potato' lifestyle); and infrequent voiding.
• Neutering - but likely related to increased risk of obesity and inactivity.
• Composition of diet: minerals, energy, moisture, metabolites, alkalinizing or acidifying.
• Concentration of urine (cats may concentrate urine up to SG 1.080 if water deprived).
• Urinary retention.

Specific

• Urinary tract infection Cystitis: bacterial (struvite).
  This is much less important in cats than in dogs. UTI is uncommon in cats unless underlying condition, eg chronic kidney disease.

• Hypercalcemia Hypercalcemia: overview (eg due to idiopathic hypercalcemia) (calcium oxalate, calcium phosphate).
• Renal tubular resorptive defect (ammonium urate).
• Portal vascular anomaly Congenital portosystemic shunt (CPSS) (ammonium urate).

Pathophysiology

• Less well-studied than in dogs.
• Depends on composition of uroliths.
• May result from single or multiple causes in an individual.

Calcium oxalate urolithiasis

• Approximately 55% of all uroliths         .
• Acidic urine pH Urinalysis: pH.
• Low magnesium, high calcium, low citrate.
• Concentrated, low volume urine Urinalysis: specific gravity.
• Hypercalcemia must be excluded when calcium oxalate uroliths identified.

Struvite urolithiasis

• Magnesium ammonium phosphate      .
• Approximately 30% of all uroliths.
• Neutral to alkaline pH urine.
• Sterile: dietary factors, eg mineral (high magnesium, high ammonia, high phosphate) content.
• Concentrated, low volume urine.
• Infection induced: infection with urease producing bacteria, eg staphylococci, plus abnormal host defenses, eg after perineal urethrostomy Urethrostomy.

Ammonium urate urolithiasis

• Approximately 7% of all uroliths.
• Renal tubular resorptive defect or portal vascular anomaly   →   increased urate excretion in some cases.
• Other possible risk factors: purine precursors in diet eg liver, increased urine ammonia, concentrated urine, retention of urine, acidic urine.

Calcium phosphate urolithiasis

• Approximately 0.5% of all uroliths.
• Conditions causing hypercalcemia   →   hypercalciuria.
• Other possible risk factors: alkaline urine, blood clots in urine.

Cystine urolithiasis

• Very rare.
• Decreased renal tubular reabsorption of cystine.

Dried solidified blood calculi

• Newly identified type of stone which likely forms due to inflammation in the urinary tract.

Timecourse

• Depends on type of urolith.

Diagnosis

Treatment

Prevention

Outcomes