Alternate Names: Stones - cystine; Cystine stones
Causes and Risks: Cystinuria is an inherited autosomal recessive disorder. The kidneys do not adequately resorb certain amino acids during the filtering process, resulting in excess excretion of these amino acids. The amino acids may precipitate and form crystals or stones in the kidneys, ureters, or bladder.
The disorder is usually diagnosed after an episode of stones, where analysis of the composition of the stones indicates cystine. Less than 3% of known urinary tract stones are cystine stones.
Cystinuria affects approximately 1 out of 10,000 people. Cystine stones are most common in young adults under age 40.
Prevention: There is no known prevention for cystinuria. Any person with a known history of stones in the urinary tract should drink enough fluids to maintain a high urinary output by day and by night, allowing stones and crystals to be excreted before they become large enough to cause symptoms. Keeping the urine alkaline diminishes the risk of cystine stones.
Symptoms:
- flank pain or pain in the side
- on one side only (unilateral) or, rarely, both sides
- often severe
- may be progressive, getting increasingly worse over months
- may travel or radiate to lower flank, pelvis, groin, genitals
- blood in the urine
Signs and Tests: Symptoms may indicate kidney stones. The physical examination is nonspecific.
Straining the urine may capture urinary tract stones when they are excreted. An analysis of the stones shows cystine. A urinalysis may show sediment and cystine crystals. A 24-hour urine collection shows excess of cystine.
An abdominal CT scan, abdominal MRI, or abdominal ultrasound may show a presence of stones in the urinary tract. An IVP may show stones in the urinary tract.
Treatment: Treatment goals include relief of symptoms and preventing the development of further stones. Hospitalization may be required if symptoms are severe.
Stones are usually passed spontaneously. The urine should be strained and the stone saved for analysis of the type of stone. The patient should drink enough fluid to produce large amounts of urine. Water is encouraged, usually at least 6 to 8 glasses per day. Consistently high liquid intake is the mainstay of treatment. Intravenous fluids may be required.
Cystine is more soluble in alkaline solution, so sodium bicarbonate or sodium citrate (or similar medications) may be used to alkalinize the urine (see sodium bicarbonate and sodium citrate and sodium). Other medications (penicillamine) may be used to increase the solubility of cystine.
Analgesics may be needed to control renal or ureteric colic (pain associated with the passage of stones).
If the stone is not excreted spontaneously, surgical removal.
Lithotripsy may be an alternative to surgery. In this procedure, ultrasonic waves or shock waves are used to break up stones so that they may be expelled in the urine (extracorporeal shock wave lithotripsy) or removed with an endoscope that is inserted into the kidney via a small flank incision (percutaneous nephrolithotomy).
Prognosis: Cystinuria is a chronic and life long condition. The incidence of symptomatic stone formation is variable but recurrence of stones is common. The disorder seldom results in kidney failure and does not affect other organs.
Complications:
Call your health care provider if symptoms indicate urinary tract stones are present.
