Kidney stones, caused by supersaturation of the urine, depends on many factors including urine pH, ionic strength and solute concentration. What this means simply is that if a patient's urine is the wrong pH, has too many crystalline components, or not enough solvent, then the patient will have a predisposition toward stone formation. The stones can be asymptomatic, or they may cause severe pain typically in the flanks due to obstruction of the passageways for urine. They may pass on their own or they may require intervention with medication or surgery. They may also lead to such complications as infection or hydronephrosis.
Struvite Stones
Struvite stones are composed of magnesium, ammonium, and phosphate. They frequently form as what are called staghorn calculi, which are large stones which fill a significant portion of the kidney. They are caused by bacteria such as Klebsiella which have the ability to split urea, the discarded form of ammonium found in urine, back into ammonium. This high concentration of ammonium in the urine results in an alkaline urine pH, which predisposes to stone formation. According to "Smith's General Urology," these types of stones are more frequently found in women with a history of recurrent urinary tract infections. Treatment requires removal of the stone because antibiotics alone will not remove all the bacteria protected by the stone, states "CURRENT Diagnosis & Treatment: Nephrology & Hypertension"
Uric Acid Stones
These stones are typically found in men with diseases such as gout. They can also be found in patients with a history of rapid weight loss or in those taking cytotoxic drugs as chemotherapy for cancer. The common factor in these causes is an elevated level of uric acid in the body. Uric acid is formed pathologically in diseases such as gout as well as normally during protein breakdown. Patients with uric acid stones typically have abnormally acidic urine. The treatment for uric acid stones is focused on maintaining a high urine volume and a urinary pH greater than 6. The medication allopurinol can help reduce uric acid stone formation in patients with gout. Often to remove existing stones a procedure called shock wave lithotripsy is used to break the stones apart and then the urine is alkalinized, which dissolves the remaining stone fragments.
Cystine Stones
Cystinuria is an autosomal recessive hereditary disease which causes an abnormal intestinal and renal tubular absorption of the amino acid cystine. This results in a very high excretion of cystine everyday and a constant supersaturation of the urine. If the patient's urine is acidic, this cystine will become insoluble and form crystals and stones. Typically this diagnosis will be made in a patient with a family history of urinary stones, according to "CURRENT Diagnosis & Treatment: Nephrology & Hypertension.". Treatment is centered on maintaining a high daily fluid intake and alkalinizing the urine. Medications may include penicillamine and captopril. Typically procedures such as shock wave lithotripsy are not effective for cystine stones and if removal is required it will need to be done with surgery. Even with optimal medical therapy, there is a high rate of recurrence.
References
- "Smith's General Urology"; Emil A. Tanagho and Jack W. McAninch; 2008
- "CURRENT Diagnosis & Treatment: Nephrology & Hypertension"; Edgar V. Lerma, Jeffrey S. Berns, Allen R. Nissenson; 2009
