Medical and surgical therapy of the cystine stone patient

The Impact of Diet on Urinary Risk Factors for Cystine Stone Formation

Despite the importance of dietary management of cystinuria, data on the contribution of diet to urinary risk factors for cystine stone formation are limited. Studies on the physiological effects of diet on urinary cystine and cysteine excretion are lacking. Accordingly, 10 healthy men received three standardized diets for a period of five days each and collected daily 24 h urine. The Western-type diet (WD; 95 g/day protein) corresponded to usual dietary habits, whereas the mixed diet (MD; 65 g/day protein) and lacto-ovo-vegetarian diet (VD; 65 g/day protein) were calculated according to dietary reference intakes. With intake of the VD, urinary cystine and cysteine excretion decreased by 22 and 15%, respectively, compared to the WD, although the differences were not statistically significant. Urine pH was significantly highest on the VD. Regression analysis showed that urinary phosphate was significantly associated with cystine excretion, while urinary sulfate was a predictor of cysteine excretion. Neither urinary cystine nor cysteine excretion was affected by dietary sodium intake. A lacto-ovo-vegetarian diet is particularly suitable for the dietary treatment of cystinuria, since the additional alkali load may reduce the amount of required alkalizing agents.

Radiopacity and hounsfield attenuation of cystine urolithiasis: case series and review of the literature

OBJECTIVES

Given the high recurrence rate of cystine urolithiasis, understanding of the radiographic stone characteristics is important in following cystine stone formers over their lifetime. However, due to their infrequent incidence, in vivo radiographic properties of cystine stones have not been well characterized. The purpose of our study is to characterize the in vivo radiographic properties of cystine urolithiasis.

METHODS

Patients with a cystine stone analysis and noncontrast computed tomography (NCCT) were extracted from our stone clinic database. Stone attenuation in Hounsfield units (HU) was measured for each stone and plain abdominal films (kidney, ureter, and bladder radiograph [KUB]) within 30 days of the NCCT prior to any intervention were reviewed by a blinded radiologist to assess whether urolithiasis could be visualized.

RESULTS

Twenty patients met our study inclusion criteria. When plotted by attenuation, two distinct groups of stone attenuation were noted for cystine stone formers (p<0.001). The largest group (n=16) had an attenuation of <550 HU (424±106 HU), while a distinct second group (n=4) was >850 HU (972±134 HU). Sixteen patients had a KUB, with 88% of the stones being visualized by a blinded radiologist. Stone size and attenuation were not significantly different between visualized and nonvisualized stones via KUB, however, the body mass index was significantly higher in the nonvisualized group (34.4 vs 26.9 kg/m(2), p=0.03).

CONCLUSIONS

Cystine stones were visualized by KUB, which has implications in post-treatment follow-up imaging. Though most cystine stones had an attenuation of <550 HU, a second distinct group of cystine stones were noted to have a high attenuation of >850 HU. HU measurements alone are not sufficient to differentiate cystine stones from other stone compositions.

Cystine calculi: challenging group of stones

Cystinuria is an autosomal recessive disorder in renal tubular and intestinal transport of dibasic amino acids, which results in increased urinary excretion of cystine, ornithine, lysine and arginine. It affects 1 in 20 000 people and is caused by a defect in the rBAT gene on chromosome 2. Development of urinary tract cystine calculi is the only clinical manifestation of this disease. Owing to recurrent episodes of stone formation, these patients require a multi-modal approach to management. The role of medical management and minimally invasive surgery was reviewed for the treatment of cystinuria.

Renal lithiasis and nutrition

Renal lithiasis is a multifactorial disease. An important number of etiologic factors can be adequately modified trough diet, since it must be considered that the urine composition is directly related to diet. In fact, the change of inappropriate habitual diet patterns should be the main measure to prevent kidney stones. In this paper, the relation between different dietary factors (liquid intake, pH, calcium, phosphate, oxalate, citrate, phytate, urate and vitamins) and each type of renal stone (calcium oxalate monohydrate papillary, calcium oxalate monohydrate unattached, calcium oxalate dihydrate, calcium oxalate dihydrate/hydroxyapatite, hydroxyapatite, struvite infectious, brushite, uric acid, calcium oxalate/uric acid and cystine) is discussed.

Effect of Cystine-Binding Thiol Drugs on Urinary Cystine Capacity in Patients with Cystinuria

PURPOSE

To determine the effect of cystine-binding thiol drugs (CBTD) on urinary cystine capacity in patients with cystinuria.

PATIENTS AND METHODS

Seven cystinuric patients performed two sets of urine collections while on and off CBTD while controlling for all other variables: diet and fluid and alkali intake. They monitored and recorded their diet for 3 days and performed urine collections on days 2 and 3. They then stopped the CBTD for 7 days. On days 8, 9, and 10, they replicated their diets of days 1 through 3 and performed two more urine collections on days 9 and 10. Two patients took D-penicillamine, four took tiopronin, and one took tiopronin and captopril. The cystine capacity was determined, and the values obtained when the patient was on and off the CBTD were compared to determine whether CBTDs affect urinary cystine capacity. To measure the cystine capacity, we used a solid-phase assay in which cystine crystals are added to the urine and incubated for 48 hours. The crystals are spun down and resolubilized in high-pH buffer, and the amount of cystine in the crystals is calculated. The solid phase will take up cystine from urine (negative cystine capacity) that is supersaturated and give up cystine to an undersaturated urine (positive cystine capacity).

RESULTS

All seven patients had significant improvement in urinary cystine capacity on CBTDs. The mean cystine capacity off CBTD was -130.6 +/- 280.8, while the value during CBTD use was 43.1 +/- 131.2 (P < 0.05). On CBTDs, two patients still had negative values, but both had important improvements. The mean urinary volumes were similar on and off CBTD, indicating adequate and similar fluid intake. Urine pH values and urinary excretion of sodium and urea also were comparable, indicating consistency of citrate intake and diet.

CONCLUSIONS

Our results demonstrate that CBTDs lower the urinary supersaturation of cystine, as shown by a less-negative or more-positive cystine capacity. Cystine capacity can be measured directly, even in the presence of CBTDs. The value of this measurement lies in the potential to monitor the response to the drug, prescribe the minimum effective dose, and potentially decrease the adverse effects often associated with CBTDs.