Is the ratio of transition zone to total prostate volume higher in African-American men than in their Caucasian or Hispanic counterparts?

Abstract

To determine if the transition zone index (TZI, the ratio between transition zone volume, TZV, and total prostate volume, as estimated by transrectal ultrasonography, TRUS) differs among African-American (AA), Hispanic and Caucasian men. The study group consisted of 104 age-matched men (36 AA, 34 Hispanic and 34 Caucasian) with lower urinary tract symptoms secondary to benign prostatic hyperplasia (BPH). A control group of 55 age-matched men, equally distributed among the three ethnic groups, but with no BPH (based on a digital rectal examination) were also evaluated. All men completed the International Prostate Symptom Score (IPSS) and a measurement of peak urinary flow rate (Qmax), prostate volume and TZV (by TRUS) and the TZI calculated. In the control group, the mean prostate volume was 20.9, 18.2 and 19.8 mL, the TZV 6.9, 4.9, and 5.4 mL and the TZI 0.33, 0.27 and 0.25 for AA, Hispanic and Caucasian men, respectively. The TZI was significantly higher in AA than in either Hispanic or Caucasian men (P < 0.03). Although there were no differences in prostate volume among the three ethnic groups with BPH, the mean (SD) TZV and TZI were significantly higher in AA men than in either their Hispanic or Caucasian counterparts, at 15.8 (7.6) mL and 0.43, 12.7 (8.1) mL and 0.37, and 13.8 (6.7) mL and 0.37, respectively. For all groups, age correlated with the IPSS (r = 0.22, P < 0.04); the mean (SD) IPSS was 14.3 (5.7), 10.2 (2.9) and 10.6 (4.9) for AA, Hispanic and Caucasian men, respectively. There was no correlation between the IPSS and either prostate volume or TZV, but there was a strong correlation with the TZI (r = 0.29, P < 0.01), regardless of race. These results suggest that AA men have a greater TZV and a higher TZI than their Caucasian or Hispanic counterparts, regardless of the presence of lower urinary tract symptoms. Studies are underway to determine if these differences are clinically significant and correlate with either subjective and/or objective parameters of BPH.