# Clinical Predictors of Response to Testosterone Replacement Therapy in Boys With Micropenis: A Retrospective Study Focusing on Penile Morphology and Hormonal Factors

## TL;DR

This study identifies penile size and glans width as predictors of how well young boys with micropenis respond to testosterone therapy.

## Contribution

The study introduces glans width as a novel predictor of treatment response in testosterone replacement therapy for micropenis.

## Key findings

- Baseline stretched penile length and glans width significantly differ among response groups.
- Glans width is a stronger predictor of treatment response than penile length.
- Testosterone therapy during mini-puberty does not significantly improve outcomes.

## Abstract

We aimed to identify clinical predictors of response to testosterone replacement therapy in boys with micropenis, focusing on initial penile measurements, hormone levels, and treatment timing relative to the mini‐puberty period.

This retrospective study included 37 boys aged ≤ 3 years with micropenis who received three intramuscular injections of testosterone enanthate (25 mg at monthly intervals) at Nagasaki University Hospital between April 2019 and March 2024. Based on post‐treatment stretched penile length standard deviation scores, the patients were classified into three response groups: good (Group 1), intermediate (Group 2), and poor (Group 3). Baseline pre‐treatment stretched penile length, glans width, hormone levels, and timing of testosterone replacement therapy were compared among the groups. Logistic regression analysis was used for identifying predictors of favorable response.

There were statistically significant differences in stretched penile length and glans width among the three groups. Although testosterone replacement therapy initiated during mini‐puberty was more frequent in Group 3 than in the other groups, this difference was not substantial. Using logistic regression analysis, we identified baseline pretreatment stretched penile length and glans width as independent predictors of treatment response, with glans width showing stronger predictive power.

Initial penile dimensions, particularly glans width, were reliable predictors of testosterone replacement therapy efficacy in boys with micropenis. Further prospective studies are warranted to optimize treatment timing and assess underlying hormonal and genetic factors.