Introduction
Cystine kidney stones are relatively rare compared to other types of kidney stones because they are caused by a rare and inheritable disease called cystinuria. Another important distinction is that they occur in children and younger adults whereas most others in older people. Treatment is available but short of a kidney transplant, a cure is not.
Knowing the Causes
Amino acids are easily filtered by the kidneys into the urine but normal kidneys are able to reabsorb them from the urine and return them to the blood. In cystinuria, there is a gene mutation or defect that decreases the kidney’s ability to reabsorb the cystine amino acid from the urine. Cystine dissolves poorly in urine and form crystals that can grow into stones.
Recognizing the Symptoms
A cystine kidney stone usually presents with pain and passing of a stone, similar to other stones. Unlike other stones, some people complain of continual pain even after the acute episode has passed.
Making the Diagnosis
Cystine kidney stones should be strongly suspected when they occur in children or young adults, especially if there is a strong family history of stones. Although they can show up on an x-ray, they are less bright than those with calcium and may be missed; an IVP or CT scan are much better at picking them up. Finding of hexagonal crystals in the urine and measuring a lot of cystine in the urine can make the diagnosis.
Understanding the Complications
The complications of cystine kidney stones are similar to other kidney stones and include: urinary obstruction (hydronephrosis), infection and rarely kidney failure.
Conservative Treatment
To decrease the concentration of cystine in the urine, a high fluid intake is recommended (typically 3 liters or more). Because cystine dissolves in urine better at a higher urine pH, the urine is usually alkanized with citrate or bicarbonate. Decreasing sodium intake to very low levels can also help.
Medications Available
If conservative treatment doesn’t work, there are several medications available (penicillamine, tiopronin and captopril) that prevent cystine being made from cysteine. Penicillamine is widely available but has a high rate of complications. Tiopronin is effective and has less side effects but it isn’t available everywhere. Captopril has the least amount of side effects but it is also the least effective of the three.
Procedure Options
If conservative treatment and medications are not effective, a procedure may be required. Because shock wave therapy is often not very effective, especially if they are larger than 1.5 cm, an invasive procedure is often required. If the stones are broken using an invasive procedure, it is usually a good idea to try and dissolve the remaining fragments by injecting penicillamine directly into the kidney. Open surgery is very rarely used.
Outcome of Treatment
Cystine kidney stones are difficult to treat and they usually cause a lifetime of trouble. On the average, you can expect 1-2 attacks per year with conservative treatment and an attack once every six months with medications. Rarely people with multiple stones will develop kidney failure, but if you do, a kidney transplant cures the disease.
