Many urologists manage patients with bladder outlet obstruction (BOO) similarly regardless of their prostate size. But a new study suggests that men with small prostates and BOO have more severe symptoms and voiding problems and similar bladder abnormalities compared with men with larger prostates.

“Our study presents thought-provoking evidences that men with LUTS/BPH with small prostates and refractory symptoms should be checked for bladder functions with urodynamic study,” stated lead researcher Seung-June Oh, MD, PhD, of Seoul National University Hospital in South Korea, and colleagues.

The investigators evaluated data from 2,039 patients with benign prostatic hyperplasia (BPH) or lower urinary tract symptoms (LUTS) refractory to medication. All patients underwent urodynamic study from 2004 to 2013 at the hospital. Patients were then divided into 3 groups by their prostate volume: small (30 mL or less), moderate (30–80 mL), or large (80 mL or greater).

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Prostate volume correlated with BOO, according to results published online ahead of print in Urology. Men with small prostates and BOO, however, had higher post-void residual urine, lower voiding efficiency, and similar maximal flow rate (Qmax) compared with men who had larger prostate glands. Urodynamic studies showed that bladder abnormalities, including low compliance and involuntary detrusor contraction, were similar regardless of prostate size. Notably, the small prostate group had more detrusor underactivity.

­­­­­­­­­­The investigators determined that serum PSA values and Qmax predicted BOO in men with small prostates. The risk of BOO increased by 34% per unit increase in serum PSA and decreased by 23% per unit increase in Qmax.

While BOO is less common in men with small prostates, it might be more severe because it has different causes, the researchers hypothesized. These include high bladder neck elevation, increased prostate-urethral angle, and elevated smooth muscle tone in the prostatic stroma.

The researchers acknowledged that the patients in this study were a select group. They encourage future studies of more general populations to confirm these results.


  1. Kang M, Kim M, Choo MS, Paick JS, and Oh J. Urodynamic Features and Significant Predictors of Bladder Outlet Obstruction in Patients With Lower Urinary Tract Symptoms/Benign Prostatic Hyperplasia and Small Prostate Volume. Urology; doi: 10.1016/j.urology.2015.11.027.