Often radiolucent when very small (<2mm). These stones become more visible as their size increases.
Cystine uroliths form because of inherited defects in renal tubular transporters of cystine and other dibasic amino acids resulting in increased urine cystine excretion. The transportation defect is genetically heterogeneous (autosomal recessive-SLC3A1 and autosomal dominant-SLC3A1 & SLC7A9) in other species and is likely similar in cats. Cystine stones are highly recurrent.
• Genetic tests for Cystinuria variants (Types 1, 2, others)
• Potassium citrate if urine pH is consistently ≤6.5.
• Cautiously consider Thiola or similar thiol reducing drugs in recurrent cases.
• Lower animal protein/sodium foods that produce neutral to alkaline urine (e.g. k/d early support, k/d, k/d + mobility, others). If needed, feed canned therapeutic foods or add water to achieve a urine specific gravity ≤1.030.
Medical imaging every 2 to 6 months to detect recurrent stones when small to potentially permit their removal without surgery.