Cho KS et al, 2015: Optimal Skin-to-Stone Distance Is a Positive Predictor for Successful Outcomes in Upper Ureter Calculi following Extracorporeal Shock Wave Lithotripsy: A Bayesian Model Averaging Approach.
Cho KS, Jung HD, Ham WS, Chung DY, Kang YJ, Jang WS, Kwon JK, Choi YD, Lee JY.
Department of Urology, Gangnam Severance Hospital, Urological Science Institute, Yonsei University College of Medicine, Seoul, Korea.
Department of Urology, Incheon Red Cross Hospital, Incheon, Korea.
Department of Urology, Severance Hospital, Urological Science Institute, Yonsei University College of Medicine, Seoul, Korea.
Department of Urology, Severance Check-Up, Yonsei University Health System, Seoul, Korea.
OBJECTIVES: To investigate whether skin-to-stone distance (SSD), which remains controversial in patients with ureter stones, can be a predicting factor for one session success following extracorporeal shock wave lithotripsy (ESWL) in patients with upper ureter stones.
PATIENTS AND METHODS: We retrospectively reviewed the medical records of 1,519 patients who underwent their first ESWL between January 2005 and December 2013. Among these patients, 492 had upper ureter stones that measured 4-20 mm and were eligible for our analyses. Maximal stone length, mean stone density (HU), and SSD were determined on pretreatment non-contrast computed tomography (NCCT). For subgroup analyses, patients were divided into four groups. Group 1 consisted of patients with SSD<25th percentile, group 2 consisted of patients with SSD in the 25th to 50th percentile, group 3 patients had SSD in the 50th to 75th percentile, and group 4 patients had SSD≥75th percentile.
RESULTS: In analyses of group 2 patients versus others, there were no statistical differences in mean age, stone length and density. However, the one session success rate in group 2 was higher than other groups (77.9% vs. 67.0%; P = 0.032). The multivariate logistic regression model revealed that shorter stone length, lower stone density, and the group 2 SSD were positive predictors for successful outcomes in ESWL. Using the Bayesian model-averaging approach, longer stone length, lower stone density, and group 2 SSD can be also positive predictors for successful outcomes following ESWL.
CONCLUSIONS: Our data indicate that a group 2 SSD of approximately 10 cm is a positive predictor for success following ESWL.
PLoS One. 2015 Dec 14;10(12):e0144912. doi: 10.1371/journal.pone.0144912. eCollection 2015. FREE ARTICLE
This is an article that emphasizes the role of skin-to stone distance SDS for successful first treatment. For the statistical analysis the authors sub-grouped the patients according to SDS in four percentiles 75%. It is not clearly stated exactly how SDS was measured, but most certainly they measured the distance from the skin level to the stone in an angle of 45 degrees to the vertical plane in a transverse NCCT image. The crucial question is of course how well this line coincided with the shockwave path.
There are two problems that need consideration. First it was stated that the proximal ureter was the segment from UPJ down to the upper level of the SI-joint. For stones in the lower part of this ureteral segment, it is likely that the longest distance was recorded, but for such stones the surrounding bone structures might absorb a lot of energy. Therefore the SDS is probably not the only variable that explains poor disintegration.
The other problem to that the authors bring attention to is the group with the shortest SDS for which the inferior results were explained by imprecise focusing. In the latter case this outcome is possibly related to the design of the lithotripter head and the geometry of the shockwave. According to the information that I obtained the EDAP device had a penetration depth of 210 mm and the Dornier device 150 mm. One possible contributing factor for the less successful results in Group 1 would be that the penetration depth is too long. To solve that problem a fluid compartment inserted between the bellow of the therapy head and the skin might be necessary for appropriate focussing.
It would also have been of interest to get some information on how many of the patients that were treated with shockwaves entering from the back and in how many patients an anterior approach had been used.