Cystine stones

Definition

Cystinuria is a disorder characterized by stones in the kidney, ureter, and bladder. It is caused by excessive excretion of certain amino acids (protein building blocks) due to a genetic abnormality. (See also nephrolithiasis).

Alternative Names

Causes

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 (solids separate from liquids) 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

Cystinuria affects approximately 1 out of 10,000 people. Cystine stones are most common in young adults under age 40.

Symptoms

• Flank pain or pain in the side or back
  • On one side only (unilateral) or -- rarely, both sides
  • Often severe
  • May be progressive, getting increasingly worse over days
  • May travel or radiate to lower flank, pelvis, groin, genitals
• Blood in the urine

Exams and Tests

Symptoms may indicate kidney stones. The doctor will not be able to determine the presence or cause of the stones with only a physical examination.

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 an excess of cystine.

An abdominal CT scan, abdominal MRI, or abdominal ultrasound may show a presence of stones in the urinary tract. An IVP (intravenous pyelogram) may show stones in the urinary tract.

Treatment

Treatment goals include relief of symptoms and preventing the development of more 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. The patient should drink enough fluid to produce large amounts of urine. Drinking water is encouraged, usually at least 6-8 glasses per day. Patients are urged to continue high liquid intake as an important part of treatment. Intravenous fluids may be required.

Cystine is more soluble in alkaline solution, so potassium citrate or potassium bicarbonate (or similar medications) may be used to make the urine alkaline. Other medications, such as penicillamine, may be used to help dissolve cystine. Eating less salt can also decrease cystine excretion and stone formation.

Analgesics (pain relievers) may be needed to control renal or ureteric colic (pain in the kidney or bladder area associated with the passage of stones).

If the stone is not excreted spontaneously, surgical removal may be necessary.

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 (side of the body) incision (percutaneous nephrolithotomy). Lithotripsy is not as successful for removal of cystine stones as it is for other types of stones.

Outlook (Prognosis)

Cystinuria is a chronic, lifelong condition. The incidence of symptomatic stone formation is variable, but recurrence of stones is common. The disorder seldom results in kidney failure, and it does not affect other organs.

Possible Complications

• Ureteral obstruction
• Kidney injury from stone
• Kidney infection
• Bladder injury from stone
• Urinary tract infection

When to Contact a Medical Professional

Call your health care provider if you have symptoms of urinary tract stones.

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.