Bladder sensory desensitization decreases urinary urgency

Bladder desensitization has been investigated as an alternative treatment for refractory detrusor overactivity. Most open and controlled clinical trials conducted with intravesical RTX showed that desensitization delays the appearance of involuntary detrusor contractions during bladder filling and decreases the number of episodes of urgency incontinence. Urgency is being recognised as the fundamental symptom of overactive bladder (OAB), a symptomatic complex which recent epidemiological studies have shown to affect more than 10% of the Western population. As anti-muscarinic drugs, the first line treatment for OAB, are far from being able to fully control urgency, the opportunity to test other therapeutic approaches is created. The present work was, therefore, designed as an exploratory investigation to evaluate the effect of bladder desensitization on urinary urgency.

Twenty-three OAB patients with refractory urgency entered, after given informed consent, a 30 days run-in period in which medications influencing the bladder function were interrupted. At the end of this period patients filled a seven-day voiding chart where they scored, using a 0-4 scale, the bladder sensations felt before each voiding. Then, patients were instilled with 100 ml of 10% ethanol in saline (vehicle solution) and 30 days later a second seven-day voiding chart was collected. Finally, patients were instilled with 100 ml of 50 nM RTX in 10% ethanol in saline. At 1 and 3 months additional voiding charts were collected. At the end of the vehicle and 3 months period patients were asked to give their subjective impression about the outcome of the treatment and about the willingness to repeat the previous instillation.

At the end of the run-in period the mean number of episodes of urgency per week was 71 +/- 12 (mean +/- SEM). After vehicle instillation, the mean number of episodes of urgency was 56 +/- 11, but only 4 patients (17%) considered that their urinary condition had improved enough to repeat the treatment. At 1 and 3 months after RTX the number of episodes of urgency decreased to 39 +/- 9 (p = 0.002) and 37 +/- 6 (p = 0.02), respectively (p indicates statistical differences against vehicle). The percentage of patients with subjective improvement after RTX and willing to repeat the instillation at a later occasion was 69%.

In OAB patients with refractory urgency bladder desensitization should be further investigated as an alternative to the standard management. Additionally, the specific effect of RTX on TRPV1 receptors suggests that urothelium and sub-urothelial C-fibers play an important role to the generation of urgency sensation.