A study of the pathogenesis, urodynamic assessment and outcome of detrusor instability associated with bladder outflow obstruction.

One hundred patients awaiting surgery for bladder outflow obstruction were studied prospectively. All patients completed a symptom score and had urodynamic studies pre-operatively. These results were not known to the urologist and did not therefore influence the course of surgery. There was a good positive correlation between both the severity and the duration of irritative symptoms and the presence of detrusor instability. Eighty per cent of patients were significantly improved 3 months post-operatively. Patients with detrusor instability or low compliance were four times more likely to have an unsatisfactory outcome than those with stable bladders. The outcome could have been predicted in half of the unsuccessful patients on the basis of their pre-operative symptom score and urodynamic studies. Whilst a full urodynamic evaluation is usually unnecessary, all patients should have a flow rate estimation and those with a high urgency symptom score and an unexpectedly high flow rate require full urodynamic assessment. These patients should be considered for alternative treatment or warned pre-operatively of the likely outcome.