This study aimed to evaluate the efficacy and safety of combining TTNS with mirabegron therapy in the treatment of women with OAB. Compared to mirabegron monotherapy, our findings indicate that combination therapy significantly enhances urinary symptoms, including urgency, frequency, and nocturia. Additionally, the safety profile of the combination therapy was comparable to that of mirabegron alone, with no significant increase in adverse events.
The tibial nerve is a mixed nerve (L4-S3) from the same spinal cord segment as the nerves innervating the bladder and pelvic floor[14]. Stimulation of the tibial nerve blocks the transmission of abnormal sensations to the spinal cord and brain, affecting and regulating the behavior of sacral innervated organs such as the bladder, urethral sphincter, and pelvic floor. In the late 1990s, Dr. Marschall Stoller proposed tibial nerve stimulation, initially known as the SANS (Stoller Afferent Nerve Stimulator) protocol, promising to treat non-neurogenic lower urinary tract dysfunction [15]. The terminology now used is percutaneous or transcutaneous tibial nerve stimulation(TTNS), depending on the electrodes used. The use of self-adhesive surface electrodes during treatment is called transcutaneous tibial nerve stimulation (TTNS).
Bladder smooth muscle activity is primarily influenced by neurotransmitters[16], and β3 adrenoceptor agonists[17] have appeared as an emerging drug commonly used to treat incontinence, urgency, and frequency of urination caused by OAB. A study found that the effect of mirabegron on OAB symptoms is similar to that of solifenacin monotherapy, and it does not increase the risk of adverse events[18].
The superior efficacy of the combination therapy could be attributed to the synergistic effects of TTNS and mirabegron. TTNS, through its neuromodulatory mechanism, potentially enhances the therapeutic effects of mirabegron on the detrusor muscle, leading to improved bladder capacity and control. This synergism aligns with the hypothesis that targeting multiple pathophysiological pathways in OAB can yield better outcomes than monotherapy. Our study showed significant improvement in all bladder diary parameters in the combination group in the sixth week and the third month. These results are consistent with previous studies suggesting the benefits of multimodal treatment approaches in managing complex conditions like OAB. Maida Zonić-Imamović et al. [19] demonstrated the effect of a single application of TTNS in patients with an idiopathic overactive bladder. There was a statistically significant improvement in all clinical symptoms, which positively affected QOL.In addition, De Seze et al. conducted a multicenter study in France[20], where 83.3% of patients showed statistically significant improvement in clinical symptoms and quality of life after TTNS treatment. Vecchioli et al. [21-22]investigated the efficacy and durability of Solifenacin (SS) with PTNS with combination therapy (PTNS+SS) for the treatment of OAB. They found that PTNS+SS was more effective than SS and PTNS separately. Booth et al.[23]designed a randomized controlled trial to evaluate the efficacy of transcutaneous tibial nerve stimulation (TTNS) for treating adults with an OAB.There were significant improvements in urgency, frequency of urination, and incontinence episodes. Our study’s findings are reassuring regarding safety, indicating that adding TTNS to mirabegron therapy does not exacerbate the risk of adverse events. The non-invasive nature of TTNS, coupled with the well-established safety profile of mirabegron, supports the clinical feasibility of this combination therapy as a therapeutic option for women with OAB.
The synergistic action of TTNS and mirabegron likely provides a comprehensive approach to modulating bladder activity both directly and indirectly. While TTNS targets the neural control of bladder function, mirabegron's role in relaxing the detrusor muscle addresses the storage symptoms of OAB, thereby offering a dual mechanism of action. While our study provides valuable insights, it is not without limitations. The short follow-up period may have affected the results. In addition, the study was based on a single center with a small sample size, which may have some sampling error. Moreover, we only counted relevant symptoms by patients' main complaints, which may have subjective bias. Future research should focus on the long-term outcomes of combination therapy, its cost-effectiveness, and its applicability to broader patient populations, including men with OAB and individuals with different OAB severities.