Comparison of parameters to determine the cause of urinary disturbance in men with prostate volume less than 20 milliliters

Background: A pressure‐flow study, although a slightly invasive procedure, can evaluate bladder outlet obstruction and detrusor contractility. This study was conducted in men with a non‐enlarged prostate to determine the cause of urinary disturbance by less invasive examinations that might eventually replace pressure‐flow study. Methods: Thirty‐six men with lower urinary tract symptoms were enrolled. Their prostate volume, estimated by transrectal ultrasonography, was less than 20 mL. All patients were examined using pressure‐flow study, free‐flowmetry, transrectal ultrasonography, prostate specific antigen and an interview using the International Prostate Symptom Score and Quality of Life Index. With determination of the cause for urinary disturbance, parameters that correlated with outflow obstruction or impaired detrusor contractility were sought. Results: Twenty‐one (60%) of the 36 men were judged as having outflow obstruction, and 16 of these 21 men had normal detrusor function. Impaired detrusor contractility was observed in 17 men. Only three of these 17 men had no outflow obstruction. Four patients had an unstable bladder. All these four had normal detrusor contractility, but had outflow obstruction. Among the parameters examined, only the maximum flow rate in a flow metrogram (Q max ) correlated significantly with the degree of outflow obstruction ( P  = 0.04). The positive predictive value of Q max for outflow obstruction was 65% at a flow rate of less than 10 mL/s, and 100% at that of less than 5 mL/s. No parameter correlated with detrusor contractility. Conclusion: The only parameter that was a clear indicator of outflow obstruction was Q max . Other indicators of detrusor contractility should be sought.