How should cystine urolithiasis be diagnosed and managed in dogs?

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Cystine urolithiasis in dogs is diagnosed by combining signalment, urinalysis, imaging, and urolith analysis, then managed through a combination of castration, dietary modification, urine alkalinization, and — in recurrent or severe cases — thiol-binding drug therapy. --- Diagnosis begins with recognizing the high-risk population. Cystine uroliths occur predominantly in intact male dogs, with 70.3% of male dogs with cystine-containing uroliths confirmed intact in one laboratory series, and 88% intact in another.113 The average age at diagnosis is 4.7 years, consistent with an inborn error of metabolism presenting in young adults.813 Predisposed breeds include English Bulldogs, French Bulldogs, English Mastiffs, Mastiffs, Pitbull Terriers, and Rottweilers, though mixed-breed dogs account for 28% of cystine urolith cases in some series.3813 Clinical signs prompting evaluation include stranguria, pollakiuria, hematuria, and urethral obstruction.1 Urinalysis is the first diagnostic step but has limited sensitivity. Cystinuria is identified on urinalysis in only 45% of dogs confirmed to have cystine stones.8 Urine pH in affected dogs averages 7.0 (range 6–8).8 Cystine has low solubility in acidic and neutral urine, and the target for prevention is urine pH above 7.2.3 Urine specific gravity should be targeted at ≤1.020 in dogs.11 Radiography is the primary imaging modality, though cystine uroliths are of low radiodensity. Cystine uroliths are generally of low radiodensity and may not be visible on plain abdominal radiographs; contrast radiography (retrograde pneumocystography or urethrocystography) is required to identify radiolucent uroliths.19 Ultrasound and urethrocystoscopy are additional options for urolith detection in the lower urinary tract.9 Definitive mineral composition diagnosis requires quantitative urolith analysis of retrieved stones, as cystine uroliths rarely contain other minerals.1 Genetic testing for Type I (SLC3A1, autosomal recessive; Labrador Retri