A possible condition of pre-instability in prostatic obstruction.

There were 40 patients with benign prostatic hypertrophy (mean age 66 +/- 9 years) who had an obstructed stable bladder on a pressure-flow study. After a mean of 18 months (range 5 to 64) urodynamic studies were repeated and 20 men (group 1, mean age 60 +/- 7 years) had a stable bladder, while 20 (group 2) who were older (mean age 71 +/- 7 years) had detrusor instability. In the latter 20 patients greater outflow obstruction was noted at the second assessment. What seems most interesting is that at time 1 group 2 patients had a significantly higher rate of increase in opening pressure, which would possibly characterize an early stage in the development of structural changes leading to detrusor instability. This finding might prove a reliable clue to predict the latter condition in men with a proximally obstructed stable bladder.