Background and purpose: Obesity has been identified as a limitation of extracorporeal shockwave lithotripsy (SWL). The obesity metrics of body mass index (BMI) and skin-to-stone distance (SSD) have been evaluated as predictors of SWL success. While SSD has demonstrated a strong correlation with success, BMI has not. Bioimpedance analysis (BIA) is an accurate way of determining body adiposity. We evaluated fat mass percentage (FMP) as measured by BIA as a predictor of SWL success.
Patients and methods: We prospectively collected body composition data using the Imp-DF50 Body Impedance Analyzer on consecutive patients undergoing SWL. All generated variables, including FMP, along with demographics, BMI, stone size, and stone composition, were analyzed. Patients were evaluated for success, defined as no evidence of stones on radiography of the kidneys, ureters, and bladder at follow-up.
Results: Fifty-two consecutive patients were enrolled in the study, of which 37 had the necessary metrics to be included in the analysis. Twenty-three (62.2%) patients were stone free while 14 (37.8%) were found to have residual stone at follow-up. There was no difference in sex, stone laterality, mean age, and stone size between the groups. For the success and failure groups, the mean BMI was 25.8 kg/m(2) and 29.8 kg/m(2) (P=0.0091), and mean FMP 24.6% and 32.2% (P=0.0034). On mirrored multivariable analysis, both BMI (OR=0.735, P=0.026) and FMP (OR=0.806, P=0.010) were associated with success. Patients with a FMP ≥35% had a reduced success rate compared with those with a FMP <35% (14% vs 73%, respectively, P=0.0028).
Conclusions: Both BMI and FMP both appear to be independent predictors of success. Based on these findings, a large study examining the relationship between BMI, FMP, SSD, and SWL success is warranted. A preoperative FMP ≥35% is associated with a 14% success rate, and alternative treatment strategies for urolithiasis should be considered.