Case Studies in Cystinuria

David S. Goldfarb, MD; Michael Grasso, MD

Disclosures

Urol Nurs. 2017;37(2):90-93. 

In This Article

Case Study 2

Patient L.S. was healthy until age 13 years. Due to some mild abdominal discomfort, which in retrospect was not related to kidney stones, he visited an emergency department. During the initial emergency department visit, a plain film of the abdomen was performed, which demonstrated several large and asymptomatic radiodensities overlying both kidneys. Although the radiologist called the stones "calcifications," he had no way to confirm their composition was actually calcium; in fact, it was not. L.S.'s urinalysis at that time showed a urine pH of 6.5, no protein, and no red or white blood cells. The urinalysis also revealed six-sided crystals, which are definitively diagnostic of cystinuria. L.S. was referred to his pediatrician, who ordered a 24-hour urine collection. The screening test for cystine was positive, and the patient was shown to have elevated levels of cystine and three dibasic amino acids: ornithine, arginine, and lysine. The mnemonic "COAL" or "COLA" is useful to recall the affected amino acids in cystinuria.

Later that year, L.S. experienced his first episode of renal colic. He returned to the emergency room, where a computed tomogram (CT) scan showed a 6 mm right distal ureteral obstructing stone.

Clinical Interaction

Ureteroscopy was performed and the stone removed. The right kidney contained several partial staghorn stones that extended into multiple renal calyces. The stones were removed by multiple PCNL procedures.

L.S. was told to increase his fluid intake to 4 L per day, restrict sodium intake to reduce cystine excretion, and limit protein intake to 100 g per day to reduce cystine and acid excretion. He was also prescribed potassium citrate 30 mEq by mouth after each meal and tiopronin 600 mg twice a day. On this regimen, his 24-hour urine collection showed 3.6 L of urine, pH 7.6, 120 mEq of sodium, and cystine excretion of 940 mg per day.

As a result of the stones, the local obstruction of multiple calyces, and multiple urologic procedures, kidney function on the right side was severely reduced. While L.S.'s serum creatinine was 1.1 mg/dL, a nuclear renal scan demonstrated that his left kidney was larger than the right and responsible for 91% of his total glomerular filtration rate (GFR) (see Figures 1 and 2). The relative lack of kidney function on the right side was evident on several occasions in L.S.'s early 20s. Over the course of two years, L.S. had four episodes of left renal colic, which were notable for creatinine increasing from normal values to 4.0 to 8.0 mg/dL. Each episode of acute kidney injury was caused by obstructive uropathy affecting the kidney that was responsible for most of his remaining total GFR. In each instance, a left ureteral stent was placed, relieving acute obstruction and returning serum creatinine to baseline values. On two occasions, L.S. was told that hemodialysis would be required, but rapid stent placement led to immediate recovery of kidney function.

Figure 1.

The right kidney is small with several stones and very little renal parenchyma. The left kidney has significant hydronephrosis.

Figure 2.

An image from the same CT scan as seen in Figure 1. This pelvic view demonstrates a left, distal ureteral stone, which is responsible for the hydronephrosis seen in Figure 1.

Given the failure of medical therapy to prevent stone formation and the resulting kidney failure, the urologist constructed an ileal ureter. In this procedure, a loop of bowel was anastomosed from the renal pelvis to the bladder to serve as a wider ureter.

Results of Clinical Interaction

Ten years later, the patient has never been admitted to the hospital again. He occasionally notes small stones or gravel passed during urination. He remains on a sodium- and protein-restricted diet, potassium citrate for urine alkalinization, and tiopronin to minimize stone formation in the left kidney. His estimated GFR is excellent, with a serum creatinine concentration of 1.0 mg/dL.

Clinical Implications

This case illustrates several important issues in the care of patients with cystinuria. Most significant is that rare genetic causes of stones are often associated with reduced kidney function. In this case, the patient lost function in the right kidney and was at risk for losing function in the left kidney as well. In the modern era of advanced minimally invasive urology, chronic kidney disease is still common in cystinuria, and end stage kidney disease requiring dialysis or transplantation, although rare, still occurs. Early identification of cystinuria should lead to early medical therapy, which may help avoid more severe stone production and its sequelae. However, some patients first present with significant stone burden, and medical therapy may not be adequate. Innovative surgical approaches may help salvage kidney function and avoid the need for renal replacement therapy.

Conclusion

In the management of rare kidney stone disorders such as cystinuria, it is important not only to institute medical therapy promptly to reduce stone production, but also to assess the potential impact of these stones on renal function. Early recognition of kidney injury resulting from recurrent obstructive stone formation can help delay or prevent the development of end stage renal disease.

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