Struvite, an amalgamation of ammonium, phosphate, and magnesium, forms a urinary mineral. These constituents, common in urine, tend to crystallize if concentrations are sufficiently high. While struvite crystals are a normal presence in the urine, complications arise when they amalgamate with mucus, culminating in a urinary plug causing male feline urinary tract blockages or forming bladder stones.
Struvite also goes by the name triple phosphate, stemming from historical mineral misidentification. This nomenclature persists, so you may encounter this term.
Pre-1980s cat food reformulations, struvite bladder stones were almost exclusively anticipated, as opposed to other mineral types. Presently, roughly 50% of feline bladder stones are struvite, with the other half composed of calcium oxalate. Accurate identification is essential for tailored treatment and prevention.
Why Do Some Cats Develop Stones if Struvite Crystals Are Normal?
Several factors contribute. Urine pH, proteins acting as crystallization nuclei, and urinary water content interact to create supersaturation with struvite. While dogs require infection for struvite stone formation, 95% of cats with struvite stones aren't infected (though stones might lead to infections.)
Identifying Symptoms
Bladder stones can emerge incidentally during unrelated evaluations or manifest with lower urinary tract disease symptoms:
- Struggling to urinate
- Blood in urine
- Inappropriate urination locations
- Frequent, small urination
These symptoms, irrespective of the lower urinary tract disease nature, indicate that roughly 25% of cats with these symptoms might have bladder stones. A bladder radiograph can verify this, while urinalysis aids in stone-type determination and ruling out other causes.
Treatment: Dietary Dissolution
Struvite stones can be dissolved through specific diets. Various commercial brands facilitate this by fostering a bladder environment conducive to struvite crystal reintegration into urine. However, patients must exclusively consume the dissolution diet. Concurrent diseases incompatible with the stone diet or consuming non-urinary foods must be absent. If one diet isn't palatable, alternatives are available—canned and dry options can be mixed, with canned diets potentially offering superior water content.
A typical protocol involves radiographs every 3 to 4 weeks to confirm stone dissolution, although some cats might achieve this in just 7 days. Failure might indicate a non-struvite composition or external food intake. On average, around six weeks are needed for dissolution. If dissolution isn't evident, surgical removal might be considered. Successful dissolution mandates a preventive diet to avert future stones.
Treatment: Surgical Solution
Surgical removal, termed cystotomy, involves opening the bladder and extracting stones. Afterward, the bladder and abdomen are closed. Post-surgery, blood in urine and initial urinary discomfort are common and addressed with pain medication.
Stones are usually sent for analysis post-surgery to confirm the type.
Alternative Stone Retrieval Methods
- Cystoscopy: This minimally invasive approach employs a cystoscope with a tiny camera. Retrieval baskets in the cystoscope remove small stones via the urethra. Laser lithotripsy breaks large stones for passage or retrieval. Limited to female cats due to urethra size.
- Voiding Urohydropropulsion: Suitable for small stones in female cats, this involves sedation, fluid bladder distension, agitation, and manual expression. Vertical positioning leverages gravity to load stones for expulsion during bladder expression. Larger stones can't pass this way.
Preventing New Stones
Urinary diets discouraging stone formation are ideal. Multiple urinary formulas exist; continuing the stone-dissolving diet can be an option. Canned formulas are advantageous due to heightened water content, promoting dilute urine—reducing crystal concentration. If dietary constraints arise, urinary acidifiers might be recommended, with pH and urine concentration monitoring to prevent struvite stone formation.
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