The international prostate symptom score (IPSS) evaluates lower urinary tract symptoms (LUTS) in men with suspected benign prostatic hyperplasia (BPH); the total score does not differentiate between storage and voiding and is unevenly weighted (four questions [57%] on voiding, three questions [43%] on storage).
To evaluate the relative contributions of storage and voiding IPSS subscores to total IPSS at baseline and in response to treatment with tadalafil.
Design, setting, and participants
Integrated analysis of data from four placebo-controlled, 12-wk studies of tadalafil (5 mg once daily) in 1499 men with LUTS/BPH.
Outcome measurements and statistical analysis
Relationships between total IPSS and the storage and voiding subscores were assessed using graphical exploration and linear regression modelling. Linear modelling was performed for the baseline and endpoint and for changes in subscores. The optimal storage subscore to total IPSS (S:T) ratio for IPSS improvement was identified using nonparametric regression and gradient-descent optimisation.
Results and limitations
The contribution of storage and voiding subscores at baseline and endpoint was 38.8% and 61.2%, and 39.2% and 60.7%, respectively. This intuitive 40:60 storage-to-voiding ratio was similar at baseline and endpoint by treatment group and for changes in subscores, but spanned the entire range for individuals. Changes in total IPSS were greatest for a storage subscore percentage contribution to total IPSS of 42.7%. There was no statistical association between S:T ratio (≥40% vs <40%) at baseline and response to tadalafil. The main limitation was the use of unvalidated storage and voiding IPSS subscores.
A constant S:T ratio of 4:10 was observed at baseline and endpoint. The greatest effect on total IPSS was noted for an S:T percentage contribution of 42.7%. Tadalafil efficacy was unaffected by the level of storage dysfunction at baseline.
This analysis shows that for men with BPH, improvements during treatment with tadalafil apply to both storage and voiding symptoms at a constant ratio. The extent of storage dysfunction before treatment did not affect the response to treatment.