The etiology of detrusor underactivity (DU) is multifactorial. Studies hypothesized that detrusor overactivity (DO) and detrusor hyperactivity with inadequate contractility (DHIC) and DU might be a sequential change of cystopathy. However, there has been no evidence to demonstrate the exact relationship between DO and DU in human subjects. This study investigated patients with DO who have been long term followed up at our clinic to investigate whether DO may progress to DU after a period of time with regular treatment.

We retrospectively reviewed 80 female patients with non-neurogenic DO and had been followed up for at least 3 years. All patients received video-urodynamic study (VUDS) in the beginning and DO was confirmed. They received regular treatment for DO at a single medical center. Because these patients had persistent overactive bladder symptoms, or had been found to have progressive lower urinary tract symptoms, a second VUDS was performed to evaluate their bladder and bladder outlet dysfunctions. During the follow-up period, repeat video urodynamic study was performed. We compared the video urodynamic parameters of the first and the latest VUDS and analysed the changes of these parameters.

The mean follow-up duration was 7.6 ± 3.9 (range 3~19.9) years, and the mean age was 59.4 ± 16.4 (18~87) years old. DU was defined by VUDS when Pdet.Qmax < 10 cmH2O and voiding efficiency (VE) less than 0.33. Among the 80 patients, 13 (16.6%) progressed to DU at the latest VUDS. The mean duration of DO progress to DU was 6.3 ± 2.7 years. In the other 67 patients, 3 (3.8%) turned to be a stable bladder, 8 (10%) was diagnosed as hypersensitive bladder without DO, and 56 (70%) were persisted with urodynamic DO. DO patient with bladder outlet obstruction (BOO, n=10, 20.4%) tended to progress to DU more than DO patients without BOO (n=3, 9.7%) (Table 1), although the duration of DO progression to DU was not significantly different between BOO and non-BOO groups (p = 0.754). Besides, we compared the patients with baseline Pdet.Qmax ≤20 cmH2O and >20 cmH2O and found a lower baseline Pdet.Qmax tended to progress to low detrusor contractility at follow-up (p = 0.028). The same trend was also found in patients with a worse baseline VE ≤ 0.33 compared to VE > 0.33 (p = 0.015) (Table 2). However, when we analyzed the duration to DO progression to DU by age, Pdet.Qmax, VE and BOO or not all showed no significant difference (Table 3).

This study found 16.3% of the DO women progressed to DU at a mean follow-up period of 7.6 years. The bladder contractility decreases with time especially in patients with BOO and DO. DO in BOO patients tends to progress to DU. DO patients with a lower baseline Pdet.Qmax or a worse baseline VE showed significantly higher rate in progression to DU. The mean duration of DO progression to DU was around 7 years, but the duration of follow-up cannot be predicted by the age, Pdet.Qmax, VE or BOO in this study. BOO might increase intravesical pressure and result in increased oxidative stress of the detrusor. In patients with DO due to BOO, the progressive oxidative stress might result in decrease of detrusor contractility and ultimately DU.

The incidence of DO progression to DU in women is high in this long- tern follow up. It seems that more DO patients with BOO will progress to DU than non-BOO patients. Patients with a lower baseline Pdet.Qmax and lower VE tend to progress to DU compared with those with a higher Pdet.Qmax and higher VE. However, the duration of follow-up was not different between patients with BOO or not.