Cystine stones

Alternative names

Stones - cystine; Cystinuria

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.

Causes, incidence, and risk factors

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 are cystine 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
  o On one side only (unilateral) or - rarely, both sides
  o Often severe
  o May be progressive, getting increasingly worse over days
  o 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 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 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. Drinking water is encouraged, usually at least 6 to 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 sodium bicarbonate or sodium citrate (or similar medications) may be used to alkalinize the urine. Other medications, such as penicillamine, may be used to increase the solubility of cystine.