One of the major treatment to manage patient with cystine kidney stones is alkalinization, although it is not as effective for uric acid kidney stones, Similar to uric acid, the solubility of cystine kidney stones is pH dependent. Most researcher agree that alkalinization could doubles the solubility of cystine kidney stones but yet will increase 10-fold solubility of uric acid, said Dr. Streem, section chief of stone disease and endourology at urology department at Cleveland Clinic Foundation, the one who bring this update to surface.
An arise from an enzymatic deficiency that is inherited as a complex autosomal recessive pattern.can be called as a reason why cystine kidney stones performed, which is l%-3% of calculi, This impairs renal and intestinal reabsorption of four dibasic amino acids: lysine, ornithine, arginine and cystine it self.
In the genetical statistic, recessive gene is approximate carry by 1 per 200 people, while the frequency would vary for worldwide statistic, started from 1 per 20,000 to 1 per 100,000 people. In normal case, unaffected person can excrete up to 100 mg/day of cystine into the urine, similar to heterozygotes. But in different case, some heterozygotes could excrete up to 400-500 mg of cystine into the urine each day, which likely develop cystine kidney stones.
In this unique homozygotes case, the treatment is rather challenging, as the development of cystine kidney stones begin, it could excrete up to 2 g of cystine per day into the urine and likely will recurrent and forming a new cystine kidney stones despite therapy. In a disulfide bond which contain in cystine, the solubility is pH dependent, a features which bring a significance effect in therapeutic. Cystine is soluble at a pH of 7, 400 mg/L, so in this point, cystine is completely soluble.
Using treatment through diet and use of thiol derivatives will reduce urinary cystine levels and by adjusting the urinary pH, the solubility of cystine in the urine can also increase. Dietary method suggests increasing the fluid intake up to 3-4 L per day, and reducing sodium consumption less than 2 g per day, to much sodium can increase the excretion of urinary cystine. The other way is to avoid food that rich with methionine. This dietary suggestion is likely easier than a precursor to cystine, which is more difficult and only have slightly effect in reducing cystine. Other common method to remove cyctine kidney stones is through surgical method, which is including percutaneous chemo-dissolution, ultrasonic lithotripsy and open surgery, which is become rarely these days.
The main part to achieve alkalinization is with balanced citrates, 60-120 mEq per day, in syrup formulation or in powder, or with potassium citrate tablets, 60-120 mEq per day, aiming for a urinary pH of 7.5-8. The other option is using sodium bicarbonate, 8-12 g per day, which is worth because it is cheaper and well tolerated, but there is a side effect of using this chemical, sodium load likely to increase calcium and cystine contain in urine. But taking a preventive action is more important, because statistically, medical instrument is less successful taking care of cystine kidney stones than with uric acid kidney stones. Patient whose never been treated previously have maximum chances of cystine kidney stone dissolution.
In the case of if patient does not respond to alkalinization and increased fluids, using thiol derivative can be work to reduce the concentration of cystine, thiol will produces cysteine disulfide, which is freely soluble, via a thiol-disulfide exchange. In alkalinization treatment on cystinuric patients, it is found that patient likely to have 1.5 stone episodes per year; which is slightly different result compare to adding a thiol derivative, which is lowers the rate to 0.5 events per year.
Compile and re-written based on article by Elizabeth Mechcatie
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