Underactive bladder and percutaneous tibial nerve stimulation (PTNS): any future?

According to the International Continence Society terminology, an underactive bladder (UAB) is characterized by a slow urinary stream, hesitancy, and straining to void, with or without a feeling of incomplete emptying and dribbling, often with storage symptoms (1). It should be differentiated from acontractile detrusor, which is still a urodynamic finding that requires to be diagnosed by pressure-flow studies. Acontractile detrusor occurs in approximately 5–17% of patients presenting with lower urinary tract symptoms (LUTS). Some studies raised the question if acontractile bladder may represent the extreme condition of detrusor underactivity, but the data did not show a proper progression from the former condition to the latter. Thus, acontractile detrusor and detrusor underactivity are actually regarded as separate conditions with similar mechanisms. Apart from psychological factors, most theories focused on afferent signaling alterations, for example, overdistension-related bladder damage leading to ischemia and oxidative stress. In such condition, myogenic detrusor alterations are supposed to be related not only to fibrous tissue and collagen accumulation between the muscle cells but also to direct myocyte cellular dysfunction (2,3).

In spite of its quite uniform presentation, UAB remains a poorly understood clinical entity on both its physiopathology and clinical management. Therapeutic approach ranges between pharmacotherapy, pelvic floor rehabilitation, surgical reduction of bladder outlet resistance, neuromodulation techniques, and, in select cases, reduction cystoplasty and latissimus dorsi detrusor myoplasty (2). None of them proved to be the golden key to the problem; so, bladder drainage by clean intermittent catheterization often remains a cornerstone for this condition and will remain so unless stem cell or gene therapy is able to change its future management (2-4).

Some further interesting insights come from animal models. A study on diabetic cystopathy in rats with voiding dysfunction showed an improvement in bladder emptying after electrical stimulation of the sensory branch of the pudendal nerve by a bipolar electrode. Depending on the stimulation intensity and treatment length, voiding efficiency improved up to 40–50% (5).

A study by Coelho et al. showed that UAB in aging rats is associated with a reduced number of serotonin-expressing cells in the proximal urethra, between the bladder outlet and the external sphincter. Moreover, the authors analyzed the effects of urethral irrigation by standard saline solution compared with urethral irrigation by 5-hydroxytryptamine solution: in the first case, occasional detrusor contractions with a mean peak of 18 cmH₂O were recorded, while in the latter the authors detected stronger repeated detrusor contractions with a mean peak of 39 cmH₂O. The authors concluded that their study somewhat showed efferent mechanisms appeared to be intact in UAB, although myogenic damage could not be ruled out in men, particularly in case of bladder outlet obstruction (6).

Several neuromodulation techniques have been proposed and investigated to LUTS over time (3,7).

In particular, after the results of anal and pudendal stimulation experiences were published by other authors during the previous years, McGuire et al. published their results in 1983 on transcutaneous electrical stimulation to treat detrusor instability (7). Four years later, but subsequently published, Cooperberg and Stoller introduced the percutaneous tibial nerve stimulation (PTNS) technique by a 34-gauge needle (8).

Over time, PTNS has been widely recognized as a valid, minimally invasive neuromodulation technique among the several clinical tools actually available in patients presenting with either neurogenic or non-neurogenic overactive bladder (OAB) (9-11).

Sparse studies have investigated the safety and efficacy of PTNS in the treatment of UAB (12). Vandoninck et al. reported their pioneering experience on 39 patients: among them, 41% showed a greater than 50% improvement in 24-hour post-void residual volume, which was the primary outcome measurement. Of note, 59% of these patients chose to continue the treatment (13).

More recently, in a randomized clinical trial, Kajbafzadeh et al. enrolled 36 children presenting with non-neurogenic UAB and proved a benefit from transcutaneous interferential electrical stimulation administered by self-adhesives placed at symphysis pubis (14).

In our previous experience, we investigated the long-term results in patients treated by PTNS for either OAB or voiding dysfunction and, in particular, patients affected with non-obstructive voiding dysfunction, all of whom showed a good global response assessment score at 7-year follow-up. The standard protocol was based on twice weekly stimulation for 6 weeks, with each session lasting for 30 minutes of electrical stimulation by 20 Hz, 200 ms energy with the lowest intensity needed to obtain a sensory or motor response (15).

A debated aspect coming from sacral neuromodulation concerns biological sex, considering some studies showed better results among female population, although these findings have not been confirmed in other experiences (16). To our knowledge, no similar data have been published about PTNS.

Chan et al. showed that detrusor acontractility seems to be an important negative predictive factor for clinical response to SNM, thus making the need for a preoperative urodynamic evaluation of bladder contractility before SNM an important patient selection and counseling tool (17).

Again, about patient counseling, another clinically frequent issue is represented by a potential UAB condition, biasing the evaluation of patients presenting with prostatic obstruction. This is a crucial point in the decision-making process before prostatic surgery because clinicians have to decide if a preliminary urodynamic test is necessary to facilitate better preoperative patient counseling. Many studies, including one by our own research group, aimed to investigate the usefulness of noninvasive urodynamic tests (18-22).

Further, the group of patients presenting with UAB is a very heterogeneous group; so, the response may be related to their underlying condition, sometimes also including the role of guarding reflex. Thus, more studies, perhaps even employing multimodal tools including electromyography, are needed to further delineate this area (23,24).

Recently, Theisen et al. studied the effects of tibial stimulation in cats presenting with either OAB or UAB, focusing on the role of frequency used for the stimulation. Interestingly, the authors found out that a low frequency (0.5–3 Hz) stimulation was able to enhance bladder contractions. Although they were not able to classify the underlying UAB mechanisms (neurogenic, myogenic, idiopathic) in their patients, the authors postulated that a low frequency repeated tibial stimulation may be of clinical interest in humans (25).

In summary, no robust data currently allow us to consider PTNS as a recommended effective treatment for UAB; however, some signals seem not to rule out its potential role in this still enigmatic bladder condition.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, AME Medical Journal. The article has undergone external peer review.

Peer Review File: Available at https://amj.amegroups.com/article/view/10.21037/amj-24-32/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://amj.amegroups.com/article/view/10.21037/amj-24-32/coif). E.F.A. is a consultant of Laborie and receives speaker honoraria from Recordati, Pierre Fabre and Convatec. He also participates on Mediterranean Incontinence and Pelvic Floor Society (MIPS) and International Continence Society (ICS). The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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