Overactive bladder is a common condition that causes a frequent, urgent need to urinate and can significantly reduce quality of life. When other treatments do not work well enough, doctors can inject a medication called onabotulinumtoxinA (a form of botulinum toxin) into the bladder wall. This procedure is often done in the office and is effective, but it can cause pain and anxiety during the injection.

Transcutaneous electrical nerve stimulation (TENS) is a non-invasive, drug-free method that uses mild electrical pulses delivered through pads placed on the skin. It is thought to reduce the sensation of pain and is already used to help with discomfort during some office procedures.

The purpose of this study is to find out whether applying TENS to the front of the lower legs (the pretibial area) reduces pain and anxiety in patients undergoing an intravesical onabotulinumtoxinA injection. Participants will be randomly assigned to one of two groups. In one group, the TENS device will be turned on (active). In the other group, the pads will be placed in the same location but the device will not be turned on (placebo). Neither the patient nor the doctor performing the assessment will know which group the patient is in.

Pain will be measured during the procedure using a visual analog scale. Anxiety will be measured before the procedure using a standard questionnaire, and patient satisfaction will be measured afterward. The study aims to enroll 68 participants in total.

Background: Overactive bladder (OAB) is a chronic urological condition that substantially impairs quality of life, and intravesical onabotulinumtoxinA (BTX-A) injection is an effective treatment option. Although performing this procedure in an office setting reduces hospital and operating room costs, the pain and anxiety experienced during the procedure can negatively affect patient comfort. Transcutaneous electrical nerve stimulation (TENS) is a non-invasive, non-pharmacological, and safe analgesic method believed to reduce pain perception through the gate control mechanism. Prior work has reported clinically meaningful reductions in pain scores when active TENS is applied during intravesical BTX-A injection; however, the effect of TENS applied specifically to the pretibial region during this procedure has not been previously investigated.

Objectives: The primary objective is to evaluate the effect of pretibial TENS on pain during office-based intravesical BTX-A injection, assessed using a Visual Analog Scale (VAS). Secondary objectives are to examine the relationship between pre-procedure anxiety level (measured with the Spielberger State-Trait Anxiety Inventory, STAI) and the pain experience, and to measure patient satisfaction using a 0-10 Likert scale.

Design: This is a randomized, double-blind, placebo-controlled trial. Participants will be randomized 1:1 using a sealed-envelope method. Envelopes will be prepared by an independent researcher not involved in conducting the study. Patients will be blinded to whether the device is active or inactive during the procedure, and blinding of the outcome assessment will be maintained.

Groups:

• Active group: TENS pads applied bilaterally to the pretibial region with the device operating in active mode.
• Control group: TENS pads applied to the same anatomical region with the device not activated (placebo).

In both groups, the intravesical BTX-A injection will be performed according to the standard routine clinical protocol without any modification.

Measurements will be collected in the following order as part of the patient's routine clinical visit:

• Before the procedure: the patient completes the Spielberger State-Trait Anxiety Inventory (STAI).
• During the procedure: pain is assessed by the performing physician using a VAS (0-10; 0 = no pain, 10 = unbearable pain).
• After the procedure: patient satisfaction is assessed using a 0-10 Likert scale.

Sample size: Based on a power analysis assuming an effect size (Cohen's d) of 0.7, a significance level (alpha) of 0.05, and power (1-beta) of 0.80, 34 participants per group were required, for a total sample size of 68 participants.

Statistical analysis: Continuous variables will be compared using the Student t-test or the Mann-Whitney U test, as appropriate. Categorical variables will be analyzed using the chi-square test. The relationship between STAI and VAS scores will be assessed using Spearman correlation. A p-value < 0.05 will be considered statistically significant.

Inclusion Criteria:

• Diagnosis of overactive bladder (OAB) with an indication for intravesical onabotulinumtoxinA (BTX-A) treatment
• No previous history of TENS application
• Age 18 years or older
• Provision of written informed consent

Exclusion Criteria:

• Presence of a cardiac pacemaker or any implanted neuromodulator device
• Impaired skin integrity in the pretibial region or peripheral neuropathy
• Pregnancy
• Coagulopathy that contraindicates the procedure, or active urinary tract infection

Individual participant data will not be shared publicly. De-identified data may be made available upon reasonable request to the corresponding author, subject to institutional and ethics committee approval.

Data will be available beginning 6 months and ending 36 months after publication of the main results.

De-identified data will be available to qualified researchers who provide a methodologically sound proposal, approved by the principal investigator and the local ethics committee. Requests should be directed to the corresponding author. A data use agreement may be required.