Aim To estimate the effect size of the prostate volume reduction after application of water vapor injections (Rezūm®) in 40 years or older patients, that have been diagnosed with Benign Prostate Hyperplasia (BPH) and are registered at UNIBE Hospital. This contrast provides a retrospective efficacy of the minimally invasive treatment valid for the local population.

Methods A retrospective study was conducted to review patient records, attended at UNIBE Hospital, in Costa Rica. Prostate volume was established as the main variable to assess BPH reversion. Other variables like the International Prostate Symptome Score (IPSS) and urinary flow rate were also evaluated for each patient. Two sample mean comparisons of baseline and follow up measures for prostate volume and IPSS were calculated to estimate a mean difference. Effect size parameters like Cohen’s d, Hedges’s g and Glass’s δ were also estimated and compared based on the standard deviation assessment. A linear regression model was also adjusted to obtain values of the statistical contribution from each of the variables included to evaluate the clinical reversal of a benign prostate hyperplasia diagnosis.

Results After data extraction from clinical records, 289 patients had complete data for this assessment, resulting in a 15% of missing values from the initial sample of records reviewed. The baseline prostate volume mean was 47 grams with a standard deviation of 14 grams, and the follow up mean was estimated at 26 grams with a standard deviation of 9 grams. After statistical comparison, this reduction was statistically significant for the observed evidence. A difference between the sample means can be expected to be as extreme as 21 grams with a p-value < 0.0001% of the times under the null hypothesis. Therefore, there is sufficient evidence to reject the null hypothesis. An IPSS of 17,47 score units (6,46 score units of standard deviation) was obtained before treatment for the 289 patient records reviewed, whereas reported IPSS after treatment was estimated with an average of 2score units with a standard deviation of 2 score units. Mean difference contrast for IPSS showed a statistically significant difference with a p-value less than 0,0001, and estimating an average difference of 14,72 score units. A change on the symptom manifestation after treatment is related with a clinical quality of life indicator. Urinary flow rate increased to an average of 19 ml/sec and a standard deviation of 5 ml/sec after procedure was applied. A linear regression model was adjusted using number of applications, age, prostate volume at baseline, IPSS at baseline and urinary flow rate at baseline; obtaining an variability explanation rate of 57% from these variables.

Conclusion There is enough evidence to expect an effective reduction on the prostate volume when applying Rezūm® water vapor therapy in Costa Rican men. IPSS also showed significant evidence to support the efficacy impact on the reduction of symptoms (mean difference was 14,72 average score units). An effect size of 21 grams of difference after applications was obtained with 1.7 standard deviations lower than the baseline measure.

Interpretation A difference in prostate volume of 20.97 average grams was obtained and quality of life was increased significantly, after REZUM treatment was applied.

The authors have declared no competing interest.

NCT06315062

The author(s) received no specific funding for this work.

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A protocol was submitted, reviewed and approved by the ethics commitee of CEC UNIBE and was registered with the code CEC-UNIBE CEC-07-2023.

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