Hypothesis / aims of study
Posterior tibial nerve stimulation (PTNS) is a useful non-invasive therapy that is indicated in patients with overactive bladder and/or chronic non-obstructive bladder retention. Its mechanism of action is thought to derive from the modulation of the S2-S4 nerve roots produced by electrical stimulation of the posterior tibial nerve, either percutaneously ("p-PTNS") or transcutaneously ("t-PTNS") using electrodes on the posterior tibial nerve (1).
Although its efficacy has been demonstrated, there are few studies that report medium- to long-term results in real practice.
Our objective is to evaluate the satisfaction and efficacy of PTNS therapy in our centre, by assessing the results of percutaneous induction therapy, as well as of a percutaneous and transcutaneous maintenance programme.
Study design, materials and methods
A retrospective observational study of patients with a diagnosis of overactive bladder (OAB) and/or chronic non-obstructive retention undergoing PTNS therapy in our centre between June 2021 and June 2022 was carried out.
Induction therapy is performed percutaneously by the nursing staff, placing a 34G needle 3-5cm cefalic to the medial malleolus. Indicators of correct stimulation are motor response, showing flexion of the first toe, and sensitive response, reporting stimulation of the foot sole. One session is performed weekly for 12 weeks. Patients complete a voiding diary prior to treatment and at week 12 of treatment.
The results of patients who complete the induction therapy are evaluated subjectively with the Likert satisfaction scale, and objectively by comparing the voiding diary. In the case of patients with a retention pattern, post-void residual (PVR) and the need for clean intermittent catheterisation (CIC) are also collected.
In patients who are satisfied with the therapy, maintenance therapy with p-PTNS or t-PTNS is indicated, and the results are also evaluated subjectively with the Likert scale. In the case of p-PTNS, therapy is continued at hospital level with a monthly session. In the case of t-PTNS, the therapy is carried out by the patient himself at home. In this case, the patient carries out at least one session per week.
A descriptive analysis of the data was performed using absolute frequency and percentage for qualitative variables, and mean (standard deviation) or median (interquartile range) according to normality in quantitative variables. The SPSS® Statistics 22.0 tool was used to perform the statistical analysis.
Results
PTNS therapy was indicated to a total of 104 patients, of whom 99 patients completed the induction treatment and are analysed in the present study.
The mean age was 65.68±14.39 years. 80(80.8%) were female and 19(19.2%) male. 21.2% had undergone previous incontinence surgery. 78(79.8%) patients had received some previous treatment for OAB (Table 1).
Therapy was predominantly indicated in patients with OAB (86.9%), either isolated (70 patients-70.7%), or associated with stress urinary incontinence (SUI) (8 patients-8,1%), voiding dysfunction (4 patients-4%) or infravesical obstruction (4 patients-4%). Chronic non-obstructive retention was the indication for treatment in 13 patients (13.1%).
Of the total cohort, only 47 patients (47.5%) submitted or adequately completed both the bladder diary for session 0 and session 12 treatment.
- Overall analysis
After induction treatment, 56 patients (56.6%) were satisfied/very satisfied, 12(12.1%) regular, and 29(29.3%) were dissatisfied/very dissatisfied (Table 2).
55 patients (55.6%) started maintenance. After a median follow-up of 11(8-14.25) months since the start of therapy, 41(74.5%) remain satisfied/very satisfied, with an overall adherence of 43 patients (78.2%). 11(20%) are regular/unsatisfied with maintenance therapy. 3(5.5%) have been lost to follow-up.
As adverse reactions, discontinuation of maintenance therapy was identified in only one patient due to pain in the lower limb.
- Patients with overactive bladder
Of the 86 patients with a clinical diagnosis of OAB, 67 underwent urodynamic study prior to initiation of therapy (78%). In 32(37.2%), detrusor overactivity was found as the main diagnosis. 13(15.1%) had SUI and 11(12.8%) had infravesical obstruction. In 19 patients (22.1%) no findings were observed.
Of the 86 patients, 46(53.5%) were satisfied/very satisfied with the induction treatment. 12(14.3%) were regular and 26(31%) were dissatisfied/very dissatisfied. 46(53.5%) started maintenance programme, of which 40(88.9%) were t-PTNS and 5(11.1%) p-PTNS.
Of the 46 patients who started maintenance, 36(78.3%) maintained adherence at the last follow-up, with 38(82.6%) being satisfied/very satisfied. Two satisfied patients did not continue with maintenance: in one case sacral nerve stimulation (SNS) was performed and the other patient discontinued therapy due to pain in the lower limb.
The patients who did not start maintenance (40 patients-46.5%) were mostly due to lack of efficacy (35-40.7%), lack of adherence (2-2.3%) or other reasons (3-3.5%).
- Patients with chronic non-obstructive retention
In the 13 patients diagnosed with chronic non-obstructive retention, an urodynamic study was performed, although in 2(15.4%) the voiding phase could not be evaluated. 10(76.9%) had detrusor underactivity.
Prior to treatment, 4(30.8%) patients were performing CIC (3 performed 2 CIC per day, and 1 patient 4 CIC per day). The median PVR was 50cc(5-195cc).
After induction treatment, 10(76.9%) patients were satisfied or very satisfied, and 3(23.1%) dissatisfied/very dissatisfied, who discontinued therapy due to lack of efficacy. The median post-treatment PVR was 10cc(0-200cc). Of the 4 patients undergoing CIC, 50% no longer required self-catheterisation.
9 patients (69.2%) started maintenance (2 p-PTNS(15.4%) and 7 t-PTNS(53.8%)). One of the patients with a good response did not start maintenance and SNS was performed.
After a median follow-up of 12 months (9-17.5), 8(100%) patients maintained treatment, 6(66.7%) were satisfied/very satisfied.
Interpretation of results
Since its first description in 1983, PTNS has been used to treat overactive bladder or chronic non-obstructive retention. The overall subjective success rate is between 56-63%, defined as improvement in quality of life, patient satisfaction or adherence to treatment (1). These results are comparable to the results of the present study, with an overall success rate after induction therapy based on patient satisfaction of 56.6%; 53.5% in patients with OAB and 76.9% in the case of voiding dysfunction, even higher than in the literature, with CIC being eliminated in 50% of cases that had previously undergone self-catheterisation.
While a good response in induction therapy is important, a sustainable maintenance system is also essential in order to maintain the benefits obtained in the long term. The literature establishes a continuation rate after initial induction of 32-79.5% (2). This study is consistent with the above, with an initial maintenance rate of 55.6%. Regarding the type of stimulation in maintenance, Dorsthorst et al (2) report that in patients receiving percutaneous inpatient maintenance, the estimated risk of loss of adherence to therapy due to logistical issues or physical discomfort is more than 40% at 6 years. In addition, a randomised study has demonstrated the non-inferiority of the transcutaneous technique compared to percutaneous (3). For this reason, transcutaneous home therapy has been favoured in our centre, achieving a 1-year adherence to treatment of 78% of responding patients.
The main limitations of this study lie in the small sample size, especially in the subgroup of retention patients, and in the difficulty of obtaining properly completed voiding diaries for their assessment. However, we believe that this fact is also a true reflection of the problems in routine clinical practice.