Often radiolucent when small (<2mm), these stones may require a combination of survey and contrast cystography to identify their composition. Stones become more radiopaque as their size increases.
Hereditary xanthinuria is a rare autosomal recessive disorder of purine metabolism caused by mutations in xanthine dehydrogenase (Type I) or molybdenum cofactor sulfarase (Type II) genes, and causes xanthine uroliths. Xanthine uroliths can also develop as an adverse effect of xanthine dehydrogenase inhibitors (allopurinol administration); however, this medication is rarely prescribed to cats. Urolith recurrence is rapid (<3 months). Many cats with hereditary xanthinuria develop nephroliths and chronic kidney disease earlier (3-6 years old) than the general population.
• Consider candidate gene (xanthine dehydrogenase and molybdenum cofactor sulfurase) sequencing for hereditary xanthinuria.
• Eliminate Xanthine dehydrogenase inhibitors (e.g. allopurinol) as a cause.
• Potassium citrate if urine pH is consistently ≤6.5 (starting dose: 75mg/kg q12-24h)
• Discontinue or reduce xanthine dehydrogenase inhibitors.
• Lower purine/protein foods that produce neutral to alkaline urine (e.g. k/d early support, k/d, others). If needed, feed canned therapeutic food or add water to achieve a urine specific gravity ≤1.030.
Urinalysis every 3 to 6 months to adjust pH to ≥ 6.5, and urine specific gravity ≤ 1.030. Medical imaging every 3 to 6 months to detect recurrent stones when small to potentially permit their removal without surgery.
We advise reviewing manufacturer's literature regarding selected therapeutic foods to determine indications and contraindications. For pets with multiple health concerns,we suggest that the selection of diet should take into consideration all health needs of the pet.