Shock Wave Treatment of Kidney Stones and Long-term Risks
Shock Wave Treatment of Kidney Stones is Associated With Long-term Risks of Diabetes Mellitus and High Blood Pressure
What is the problem and what is known about it so far?
Shock wave lithotripsy (SWL) is the use of repeated sound waves to break apart stones located in the kidneys and urinary tract. Since its introduction to the United States in 1984, it has become the preferred therapy for the majority of patients with kidney stones because it is minimally invasive and presumed to be safe. Nevertheless, concerns have been raised about potential damage to the kidneys and surrounding organs in the short and long term.
Why did the researchers do this particular study?
Previous studies have shown conflicting results, and the long-term effects of SWL on the kidneys and surrounding organs were unknown.
Who was studied?
288 patients (182 men and 106 women) who received SWL for kidney stones at the Mayo Clinic in 1985 were compared with another group of 288 patients who were chosen by the investigators to be similar in age, sex and time waited until surgery but they had had an alternative treatment to SWL (control group). Many stones in this group had passed out in the urine without treatment.
How was the study done?
The investigators reviewed their records for 1985 when SWL was first provided at the Mayo Clinic. They found 630 patients who had received SWL for kidney stones. Of these patients, 578 were thought to be still alive after 19 years and were sent questionnaires. The questionnaire was designed to measure all possible adverse effects associated with SWL, as identified by a review of the literature. A total of 288 patients responded to the questionnaire. The typical respondent had a single calcium stone on one side, most often located in the kidneys. Most respondents received a single treatment with fewer than 2.000 shock waves from a HM-3 lithotriptor. Information about the controls was obtained from review of the medical records. Outcomes after 19 years in the two groups were compared.
What did the researchers find?
48 out of 288 patients who received SWL developed new onset diabetes after 19 years follow up, compared to 19 out of 288 in the control group. In other words, the long-term risk of developing diabetes was three times greater if a patient received SWL. While initially the control group had more obese patients, 19 years later this was reversed so that more patients who received SWL were obese. Even after accounting for this increase in obesity, the patients receiving SWL were still at greater risk for developing diabetes. The risk was greater if a patient received more shocks or more intense treatment. Also at the 19 year check up the patients were examined for high blood pressure and 103 out of 280 patients who received SWL developed high blood pressure requiring medication. Only 79 out of 288 in the control group required high blood pressure medication after 19 years. In other words, the long-term risk of developing high blood pressure requiring medication was almost one and a half times greater if a patient received SWL. This risk was found to be higher in patients who received SWL on both sides.
What were the limitations of the study?
The study’s design has a number of limitations. Patients who received SWL in 1985 but died before the study was started in 2004 cannot be included. These may have been some of the sickest patients with important adverse effects that were not noted. Patients who did not respond to the questionnaire were also not included. Questionnaires themselves can introduce bias by measuring only what a patient recalls. Thus, the study design may have selected motivated, healthier patients and relied on their recollection of past events. Furthermore, questionnaires were only used for patients who received SWL, while a chart review was used to gather information about the control group. Another limitation of this study is the process of choosing patients for the control group. The investigators chose patients of similar age, sex and time waited before treatment. It cannot be guaranteed that this group was not different in other ways that could account for the differences found. For instance, there may have been other reasons why patients in the control group elected to have an alternative treatment. Finally, generalizations from this study are limited to patients who received SWL at a single medical center using the HM3-Lithotriptor. Most centers now use different lithotriptors to produce shock waves with a narrower focus. A narrower focus lessens the exposure of surrounding organs to the shock waves, however it may also be less effective at breaking apart stones.
What are the implications of the study?
This study found that Shock Wave Lithotripsy was associated with an increased long-term risk of diabetes. The risk of diabetes is increased regardless of whether a patient is obese. A greater number and intensity of treatments was associated with greater risk for diabetes. SWL was also associated with an increased risk of high blood pressure requiring medication, especially if the treatment was done on both sides.
This study offers a unique long-term perspective on the risks associated with SWL. However, limitations in this study’s design necessitate other study designs at different medical centers to confirm its findings and to identify an exact causal relationship. One possible explanation is that the pancreas is also exposed to damage from the shock waves, ultimately causing diabetes. Similarly, damage to the kidneys from the shock waves may cause an increased risk for high blood pressure - especially if both kidneys are affected. Such relationships still need to be studied.
Shock Wave Lithotripsy continues to be a popular, minimally invasive treatment option for kidney stones. However, patients considering this treatment should be informed of the possible risks suggested by this study and should be made aware of alternative treatment options that are available.
Summarized by Michael S. Ashton, College of Medicine, University of Vermont.
Summarized from "Diabetes Mellitus and Hypertension Associated With Shock Wave Lithotripsy of Renal and Proximal Ureteral Stones at 19 Years of Followup." Krambeck, A.E. et al. The Journal of Urology, May 2006, Volume 175, pages 1742-1747.
