Transition Zone Index of the Prostate as an Indicator of Bladder Outlet Obstruction and a Predictor of Response to Medical Treatment in Symptomatic Benign Prostatic Hyperplasia

Abstract

The purpose of this study was to assess the correlation between the transition zone index (TZI) of the prostate and lower urinary tract symptoms in men with benign prostatic hyperplasia (BPH), and the value of the TZI in predicting treatment outcome. Two hundreds and twenty-five men(mean ± SD age, 66.9 ± 7.7years) received treatment for 6 months with dibenyline (10 mg bid), finasteride (5 mg gd), or dibenyline and finasteride. Parameters of durinary flow obstruction and prostatic volume were evaluated before and at the end of treatment. The pretreatment symptom score (IPSS), maximal flow rate (Qmax), and total prostatic volume were used as parameters of obstruction. Total prostatic volume, Transition zone volume, and TZI were used as prostatic volume parameters in transrecastal sonography. Correlations between obstructive and prostatic volume parameters were analyzed using multiple regression. TZI showed significant correlations with age(P=0.017), IPSS(P=0.02), Qmax(P=0.02), total prostatic volume (P=0.00), and transtition zone volume (P=0.00). Transition zone volume was correlated with age (P=0.019) and IPSS(P=0.02), whereas total prostatic volume correlated only with age(P=0.021). The mean total prostatic volume was 27.9 ± 15.4 mL, the transition zone volume was 10.4 ± 85mL, and the TZI was 0.34 ± 0.11, indicating patients had, on average, small prostates despite their severe symptoms. High TZI values were associated with improvement of IPSS in patients treated with finasteride alone (P＜0.05), and in those treated with combined drugs (P=0.007). A higher TZI was also noted in patients with increased Qmax values who were treated with finasteride alone (P＜0.05). Total prostatic volume and transition zone volume were significantly higher only in patients with IPSS improvement who were treated with combined drugs. TZI was the most reliable parameter among all prostatic volume parameters for assessing symptomatic BPH. A higher TZI not only indicated a severe bladder outlet obstruction caused by BPH, but also predicted a favorable response to finasteride and combination treatment. (Tzu Chi Med J 1997;9:249-258)