Clinical and Health Affairs
Treating Urinary Tract Stones
Common Questions about a Common Problem
By Manoj Monga, M.D.
Abstract
Urinary stones are a common and costly problem. Although shockwave lithotripsy is the mainstay of treatment for stones, a number of other surgical tools and approaches may be beneficial to some patients. Newer diagnostic techniques and technologies are improving our ability to determine the size, location, and composition of stones and, thus, our approach to treatment. And an increased focus on diet and metabolism is helping patients prevent stone formation. This article reviews the current approaches to diagnosing and treating urologic stones and answers questions primary care physicians often ask about this topic.
Urinary tract stones are a common urologic problem in the United States. The lifetime prevalence of urolithiasis is 13% for men and 7% for women in this country, and the risk for stones is on the rise.1,2 An estimated $2.1 billion was spent on individuals with claims for a diagnosis of urolithiasis in 2000, which was 50% more than in 1994.1 The risk of stone recurrence is as high as 50% at five-year follow-up.3 Alhough shockwave lithotripsy remains the mainstay of treatment for stones, some patients benefit from an endoscopic approach to their stone. Recent advances in our ability to identify which patients benefit from which procedures are guiding our approach to treatment. In this article, we will review current concepts in the diagnosis and management of symptomatic stones and the role of diet and medications in stone prevention.
What are the indications for extracorporeal shockwave lithotripsy (ESWL)? In general, a patient with a stone less than 15 mm in size is a suitable candidate for shockwave lithotripsy. Patients with stones larger than 15 mm who elect to undergo ESWL are often stented to minimize the risk of ureteral obstruction, and they will be counseled that they have more than a 40% chance of needing a secondary procedure. A stone located in the lower pole of the kidney bodes unfavorably for a stone-free result: 64% for stones smaller than 1 cm and 20% for stones larger than 1 cm in size.4 Stone clearance from the lower pole can be improved by having the patient lie prone at a 45-degree angle and performing percussion of the flank. A Hounsfield unit measure of more than 1,000 on CT indicates a hard stone—leading to a greater chance of residual stones and a greater chance of larger stone fragments. A skin-to-stone distance of more than 10 cm on CT scan may lessen the efficacy of the shockwave.
Stones of certain compositions are not good candidates for ESWL. Cystine stones are often refractory to shockwave fragmentation and should be removed with endoscopic procedures such as ureteroscopy or percutaneous nephrolithotomy if greater than 1.5 cm in size. Because uric acid stones can sometimes be dissolved, urine alkalinization may be the first treatment choice for stones of this type.
What are the side effects of ESWL?
The immediate risk associated with ESWL is bleeding. There is a 1 in 1,000 risk of a serious bleed that may require hospitalization and transfusion; this risk is greater in patients older than 65 years of age and those with uncontrolled hypertension.5,6 The relationship between ESWL and the development of diabetes has not been well-established to date; one study reports a correlation, while three others refute this relationship.7,8 No study to date has demonstrated a long-term impact on renal function, although a study we recently completed confirms a 1.4-x increased risk of development of hypertension following ESWL.9 It is unclear as to whether this risk can be attributed specifically to ESWL or if it is a manifestation of a link between the pathophysiology of stones and hypertension; indeed, patients with stones in general have a higher risk of developing hypertension.
What should a primary care physician do, if anything, about asymptomatic stones found incidentally?
Patients should be counseled on the alternatives for treating asymptomatic stones. In general, patients with asymptomatic renal stones smaller than 5 mm in size should be encouraged to observe their stones. Patients with renal stones larger than 5 mm in size have a lower chance of spontaneous passage and, as such, should be counseled about the alternatives of observation, shockwave, and endoscopic procedures. The guideline for determining the chance of a stone passing is 10 minus the stone size times 10. For example, the chance that a 3 mm stone will pass is 10-3 x 10, or 70 percent. The main advantage of considering ESWL in the presence of an asymptomatic renal stone greater than 5 mm in size is that it minimizes the risk of needing a ureteral stent. Eighty percent of patients with a ureteral stent experience discomfort, and most who have had a stent appreciate the chance to avoid having to have another one.
We followed 300 patients with asymptomatic renal stones for four years and reported a 77% risk of progression, defined as stone growth, development of symptoms, or need for surgery.10 The risk for stone growth was highest if the stone location was in the lower pole. The risk for progression overall was highest for stones greater than 15 mm in size and those located in the renal pelvis. Stones smaller than 4 mm in the upper pole did not require intervention over the four-year study period.
Do all stone patients deserve a metabolic workup? If so, which tests should be done?
All patients should be offered a metabolic workup. Those who have had only one stone (no additional asymptomatic stones on CT scan) can often be given empiric dietary recommendations such as increasing fluid intake, restricting sodium, drinking citric juices, and having adequate calcium intake. They can usually forgo a more-detailed evaluation. If the patient is in a higher-risk category (African-American, pediatric, has enteric malabsorption, or has a family history of stones) or has multiple stones, then a full metabolic workup should be completed.
Two 24-hour urine collections are recommended. One collection is considered inadequate because of the high rate of discordant findings. Specialized laboratories (Litholink, Specialty labs, Urocor, Quest, Labcorp, Dianon) offer stone risk analyses; they provide not only traditional excretion values (eg, calcium, oxalate, sodium, citrate) but also supersaturation values for common stone compositions. One should be selective in ordering serum evaluations; uric acid should be obtained if the stone composition is predominantly uric acid or if the 24-hour urine test demonstrates hyperuricosuria. Calcium and PTH should be obtained if more than 50% of the stone is composed of calcium phosphate or if the 24-hour urine test demonstrates hypercalciuria. The 24-hour urine analyses should then be used to direct patient-specific dietary and/or pharmacological recommendations. What are the most challenging cases to treat?
All stones have the potential to pose significant challenges. However, the following conditions and contributing factors can make it more difficult for physicians to treat patients with stone disease:
Morbid obesity. Obesity may preclude the use of shockwave because of the depth of the stone. Preoperative and intraoperative imaging as well as patient positioning for surgery may be more difficult in these patients, and they have greater perioperative risk.
Anticoagulation therapy. Because ureteroscopy carries the lowest risk of bleeding, it is recommended for patients who cannot be taken off anticoagulation therapy. The indications for ureteroscopy (stone size less than 15 mm) are often broadened to include these patients.
Transplant kidneys, pelvic kidneys, or horseshoe kidneys. In patients with anatomic variants, stone clearance after ESWL may be more difficult. In addition, ureteroscope manipulation in the kidney may be more challenging for the surgeon because of the malrotated renal axis. Percutaneous access may require ultrasound guidance to avoid the bowel or other organs.
Pregnancy. The likelihood of hypercalciuria and stone formation increases during pregnancy. Yet because imaging and anesthesia carry a risk for the fetus, diagnosis and management of flank pain and hydronephrosis is challenging. And physiologic hydronephrosis of pregnancy may masquerade as an obstructing stone.
Chronic pain with nonobstructing stones. This requires a coordinated approach among the primary care physician, urologist, pain specialists, and others. Although surgical options may be considered, it is important that realistic expectations should be emphasized; it is possible that their pain may persist. Therefore, complementary approaches to pain management should be considered prior to intervention.
Medullary sponge kidney. Patients with this condition often pass multiple stones, and the large stone burden may hamper prophylactic treatment with ESWL or endoscopic procedures. Often, a thin membrane covers the dilated collecting ducts and hinders the surgeon’s ability to identify and remove stones.
Calyceal diverticulum stones. Upper pole diverticulum stones smaller than 15 mm can be addressed through a ureteroscopic approach. Lower calyceal or larger diverticulum stones may require percutaneous or laparoscopic treatment.
The complexity of a stone surgery is often difficult to predict, and urologists are often faced with the need to adapt to unexpected challenges and alter the course of surgery. All patients should be counseled prior to an endoscopic procedure that the surgeon might need to place a ureteral stent and perform a second surgery one to two weeks later to try to remove the stone.
What is the preferred treatment for bladder stones?
Bladder stones smaller than 2 cm can be managed cystoscopically. For men, stones 2 cm to 4 cm in size may require a percutaneous approach to minimize the risk of urethral stricture from a long cystoscopic procedure. For stones larger than 4 cm, a small open suprapubic incision is often recommended for stone extraction. It is important to determine the cause of a bladder stone (benign prostatic hyperplasia [BPH], neurogenic bladder, foreign body) and treat it accordingly. For patients with BPH, it is possible to try medical therapy (alpha-blockers and/or 5-alpha reductase inhibitors) along with stone removal rather than proceeding directly to a surgical resection of the prostate.
Conclusion
Urologic stone disease is a common disorder that results in great pain and expense. For recurrent stone formers, the collaborative efforts of primary care physicians, urologists, nephrologists, radiologists, emergency physicians, pain specialists, and dieticians are critical to decreasing the risk of stone recurrence, limiting the amount of radiation exposure a patient receives, and decreasing the morbidity associated with multiple surgical procedures. MM
Manoj Monga recently was appointed the director of the Steven Streem Center for Endourology and Stone Disease at the Cleveland Clinic. He formerly was the Joseph Sorkness Professor of Urologic Surgery at the University of Minnesota.
References
1. Pearle MS, Calhoun EA, and Curhan GC. Urologic diseases in America project: urolithiasis. J Urol. 2005;173(3): 848-57.
2. Stamatelou KK, Francis ME, Jones CA, Nyberg LM, Curhan GC. Time trends in reported prevalence of kidney stones in the United States: 1976-1994. Kidney Int. 2003;63(5):181723.
3. Uribarri J, Oh MS, Carroll HJ. The first kidney stone. Ann Intern Med. 1878;111(12):1006-9.
4. Albala DM, Assimos DG, Clayman RV, et al. Lower pole I: a prospective randomized trial of extracorporeal shock wave lithotripsy and percutaneous nephrostolithotomy for lower pole nephrolithiasis-initial results. J Urol. 2001;166(6):2072-80.
5. Knapp PM, Kulb TB, Lingeman JE, et al. Extracorporeal shock wave lithotripsy-induced perirenal hematomas. J Urol. 1988;139(4):700-3.
6. Dhar NB, Thornton J, Karafa MT, Streem SB. A multivariate analysis of risk factors associated with subcapsular hematoma formation following electromagnetic shock wave lithotripsy. J Urol. 2004;172(6 Pt 1):2271-4.
7. Krambeck AE,Gettman MT,Rohlinger AL, Lohse CM, Patterson DE, Segura JW. Diabetes mellitus and hypertension associated with shock wave lithotripsy of renal and proximal ureteral stones at 19 years of followup. J Urol. 2006;175(5):1742-7.
8. Makhlouf AA, Thorner D, Ugarte R, Monga M: Shockwave lithotripsy not associated with development of diabetes mellitus at 6 years follow-up. Urology. 2009;73(1):4-8.
9. Barbosa P, Makhlouf A, Thorner D, Ugarte R, Monga M. Shockwave lithotripsy associated with higher prevalence of hypertension. J Urol. 2010;183(4):Supplement, Page e562, Abstract 1459. 10. Burgher A, Beman M, Holtzman JL, Monga M: Progression of nephrolithiasis: long-term outcomes with observation of asymptomatic calculi. J Endourol. 2004;18(6):534-9.