Urethral injection therapy: what is the mechanism of action?

The mechanism of action of injection therapy is virtually unknown. Urethral Pressure Reflectometry (UPR) is a novel technique for measuring pressure and cross-sectional area in the urethra. UPR which provides reliable physiological meaningful parameters was used to study the mechanism of urethral injection therapy.

Fifteen patients with stress urinary incontinence (nine women) and mixed incontinence (six women) were investigated with UPR before and 101 days after urethral injection therapy. The patients subjectively judged if their stress and urge symptoms were cured/improved almost unchanged or worsened.

Ten women were cured/improved after the injection therapy. None became worse. Six patients had urge symptoms before injection therapy which did not change after the procedure. The patients were divided into two groups based on their subjective assessments of effect. One group with effect (10 women) and 1 group without effect (5 women). The patients had significantly higher squeezing opening pressure after the treatment. The other parameters were unchanged. The mean squeezing opening pressure increased significantly (P < 0.01) more in the group of patients with effect (10.6 cmH(2)O) than in the group without effect (-1.6 cmH(2)O).

Injection therapy may work by increasing the power of the urethral sphincter. The bulking material may function as additional central filler volume which increase the length of the muscle fiber and thereby the power of the sphincter.