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.
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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