Cystinuria

Abstract

Cystinuria is an autosomal recessive disorder of proximal tubular dibasic amino acid transport. Because cystine is poorly soluble in the urine, recurrent stone formation occurs, leading to significant morbidity. This disorder presents often in childhood with the average age of first stone 12–13 years old. Prevention of recurrent stone disease is critical to achieve lifelong and includes extremely high fluid intakes both during the day and overnight to maintain high urine flow and increase cystine solubility, alkalinization to a pH of greater than 7 to increase cystine solubility, and cystine binding drugs such as tiopronin or d-penicillamine. Monitoring includes specialized 24-h urine collections for cystine excretion, supersaturation and capacity as well as other measured parameters to assess efficacy of medical therapy and patient compliance, and outpatient visits at least twice yearly, but more frequently until metabolic control is achieved. Visits should include ultrasound to help to determine ongoing metabolic control and occult stone formation, as well as help to reinforce the need for compliance with medications and fluid intake. Appropriate surgical therapies include ureteroscopy with laser lithotripsy, and percutaneous nephrostolithotomy with laser lithotripsy. Extracorporeal shock wave lithotripsy is often not effective due to stone density. Given that this disorder presents in childhood and results in a lifelong risk of recurrent nephrolithiasis, treatment of cystinuria may be best managed in a specialty stone clinic with nephrologists familiar with medical management and urologists familiar with surgical management of these complex patients.