Study design, materials and methods
This is a retrospective, single-center study of patients with a clinical and urodynamic diagnosis of iUAB without bladder outlet obstruction (BOO) who are on the waiting list for SNM. The patients followed a 3-week TTNS treatment. A one-hour long session per day was completed for the first week, followed by 3-4 hour-long sessions daily for weeks 2 and 3. Voiding diaries (daily urinary frequency, voided volume per micturition, number of daily self-catheterizations and postvoid residual volume (PVR)) were collected at baseline, week 1 and week 3. Once the TTNS treatment was completed, the patients were offered to undergo bilateral PNE.
Changes in iUAB symptoms were measured with a validated scoring instrument [Patient Global Impression of Improvement (PGI-I)]. Baseline demographic variables, urodynamic parameters such as bladder contractility index (BCI), previous treatments and adverse effects were also collected.
Success after TTNS treatment was defined as an improvement of at least 50% in either one of the bladder diary parameters, and failure if none of the bladder diary parameters was improved by 50%.
Descriptive data were reported as median values and percentiles when they were quantitative or with counts and percentages when they were qualitative.
Results
A total of 26 patients were included in the study. The median age was 67 years old (IQR 53- 70) and 20(83%) were male. The median bladder contractility index (BCI) was 62(IQR 25.2-69.5).
22 patients completed their bladder diaries. Overall, 10(38%) patients had an increase in voided volume per micturition; 17(65%) patients saw an increase in their daily voiding frequency; 13(50%) patients had a decrease in the post-void residual volume (PVR), and 5(19%) saw a decrease in the number of daily self-catheterizations (see Table 1).
16 patients had PNE after the TTNS trial. 4(25%) had a failure and 12(75%) had a success. The 10 patients who did not have PNE either refused the latter or are still on the waiting list to have it (see Table 2).
Of the patients who completed their bladder diary, TTNS was a success in 10 (45%), and was a failure in 12(55%) of them.
13 patients both completed their bladder diaries and underwent PNE. 8(62%) of them had comparable results (either both success or both failure). 1(8%) patient had success with TTNS only, and 4(31%) had success with PNE only (see Table 2).
21 patients completed the PGI-I questionnaire. 3(14%) had a score of 2 (much improved), 8(38%) had a score of 1 (somewhat improved) and 10 had a score of 0 (no improvement).
18 patients both completed the PGI-I questionnaire and their bladder diaries. 12(67%) patients had comparable results (success at TTNS and improvement reported in the PGI-I, or failure at TTNS and no improvement in the PGI-I). 3(17%) patients noted an improvement in the PGI-I, but TTNS was considered as a failure with objective measures.
Interpretation of results
Despite the fact that it can have damaging health impacts such as lower urinary tract symptoms (LUTS), urinary tract infections, urinary retention and renal failure, and that it generates negative effects on quality of life, iUAB remains relatively underresearched [1]. Treatment options for iUAB are sparse and often unsatisfactory. SNM is the only FDA approved treatment for non-obstructive urinary retention [2]. Studies have demonstrated the effectiveness and safety of TTNS in overactive bladder (OAB), but no clinical trials have been reported for iUAB. TTNS has gained popularity over percutaneous tibial nerve stimulation (PTNS) on OAB because it is less invasive, easier to apply and convenient to patients. Thus, it could lead to greater patient compliance.
This study explores the feasibility of TTNS compared to PNE for iUAB patients without BOO. Indeed, a good proportion of patients saw improvements in all bladder diary parameters. There is also a considerable range and variability of responses among patients. Further studies looking at baseline demographic and/or urodynamic characteristics of patients in order to better understand this variability would be interesting.
The reason why sessions were increased from 1 hour to 3 hours between week 1 and week 3 was to better reproduce the continuous stimulations of PNE and SNM. The increase in duration of treatment
also aimed to increase the effectiveness of TTNS. Our results show that the voided volume, voiding frequency and PVR were improved with increased duration of TTNS sessions. On the other hand, the number of daily self-catheterizations remained stable regardless of the duration of sessions.
PNE and TTNS showed comparable results in a little more than half of the patients, but PNE still seemed to be more effective in others. Although larger studies would be needed to confirm it, our study demonstrates that TTNS could also be used as a tool to better select patients for SNM. In addition, TTNS is much less invasive, time-consuming and costly than PNE [3].
More than half of the patients noted a subjective symptom improvement. It is also interesting to note that some patients reported an improvement on the PGI-I questionnaire but were considered a failure to TTNS based on objective measures. This study highlights the importance of measuring patient satisfaction, and not only evaluating objective measures as a surrogate for success.
Our study is not without its limitations, such as the small sample size, the absence of a control group and the possibility for selection bias.
Despite this, our study demonstrates the potential effects on voiding symptoms for iUAB patients without BOO. Further studies with greater power and/or conducted prospectively should be pursued to better assess its clinical efficacy.