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Search Spring 2015

No Stone Unturned: A One-Two Punch to Cystinuria

Date: April 23, 2015

Michael Choi uses medical and dietary therapy to help prevent formation of cystine stones.
Michael Choi uses medical and dietary therapy to help prevent formation of cystine stones.

Kidney stones are a painful reality for a growing number of Americans, and treatment is particularly tricky for the 1 percent of adults with stones caused by cystinuria. That’s because cystine stones are extremely hard, meaning lithotripsy is not effective at breaking them into smaller pieces so they can pass.

What’s more, because cystinuria has genetic origins—it’s caused by a genetic defect that impairs the body’s ability to reabsorb cystine and other amino acids from the urine—the resulting kidney stones present a recurrent problem that can start in childhood or adolescence and last a lifetime.

“Once cystine stones are made in the body, there’s no medical treatment,” says nephrologist Michael Choi. “What we try to do is prevent them from occurring.”

Choi has teamed up with urologist Brian Matlaga to create a successful one-two punch strategy that combines surgical treatment with long-term prevention and medical management of cystine stones.

Matlaga most often relies on ureteroscopy to see the stone. Once he locates the stone, he inserts another instrument through a channel in the ureteroscope to grab the stone and remove it. Then, he and Choi work together to try to prevent stones from reoccurring, using medical and dietary therapy.

Choi begins by encouraging patients to dramatically increase their fluid intake. “People with cystinuria have 10 times the normal amount of cysteine in their urine, so one thing we try to do is to get the concentration to a safer zone,” he says. For some patients, that means drinking as much as four liters of fluid per day to reach the proper concentration, which is difficult to do, he notes.

In addition, he advises patients to drastically lower their sodium intake, which also can be challenging. “A typical American diet has about 3 to 6 grams of sodium in it per day,” says Choi. “To help with cystinuria, just 1 gram a day is suggested. That is also very hard to reach.”

Though he doesn’t typically like to turn to medication when treating traditional kidney stones, patients with cystinuria present an exception.

The pharmaceutical options in Choi’s arsenal include potassium citrate—which can have uncomfortable gastrointestinal side effects—and tiopronin, penicillamine or captopril. These drugs, too, can be difficult for patients to tolerate, but over time Choi says he tries to find the right combination of medications for each patient.

Periodically, patients will see Matlaga for imaging to see if any new stones have formed. The duo also occasionally run a stone profile to ensure that the medical therapy is working and that the medication regimen itself—particularly potassium citrate—isn’t causing the formation of new stones.

Over the last decade, Matlaga and Choi have used this joint approach on dozens of patients with great success.

“What we hope to do is decrease the stone frequency for patients who may pass hundreds of stones,” says Choi. “For some, we’re very lucky and they don’t have stones for years.”

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