Magnetic stimulation is a method approved by the FDA as a conservative approach to treating UI, which is not believed to cause serious side effects. According to the EAU guidelines, MS is still not recommended as a treatment method owing to the lack of methodologically sound studies that scientifically evaluate findings on the efficacy and long-term effects of the treatment [4].

The systematic literature review from 1998 onward revealed only five published studies that analyzed the efficacy of MS treatment for UUI, ranging from 2003 to 2019. Only Yamanishi et al. conducted a randomized, controlled trial (RCT), but this study did show a statistically significant difference in the efficacy of MS treatment for UUI between the treatment and control (sham treatment) groups. The number of incontinence episodes per week was lower, as was the number of daily voids, and the QoL improved. The other studies had similar conclusions. Their results confirmed that MS is an effective and non-invasive way to treat UUI [11, 18,19,20,21].

Answering the research questions posed here leads to further discussion and joint conclusions. Each of the studies reviewed has its limitations, which are presented in Table 1 and are the answer to Q4. These limitations should be considered when interpreting the results published in the studies. First, and perhaps most importantly, most samples, except for the study by Yamanishi et al., were nonrandomized [20]. Although this nonprobability sampling method is the most applicable and widely used method in clinical research, the sampling method does not guarantee equal chances for each subject in the target, it is less representative of the target population, and it decreases the ability to draw completely impartial conclusions about the effectiveness of MS [22]. Second, the power of most studies in our SR was low (Table 1). An ideal study is one that has high power. This means that the study has a high chance of detecting a difference between groups if it exists, and consequently, if the study demonstrates no difference between groups, the researcher can be reasonably confident in concluding that none exists. According to the literature review, the ideal power for any study is considered 80%. For example, for the study by Lukanović et al. [11], to achieve a significance level of 95% and a power of 80%, the sample size should equal 189 [23, 24]. Only the study by Yamanishi et al. included more than 100 patients; precisely 151 [11, 20]. This means that all other studies in our SR had low power, and studies with lower power increase the likelihood that a statistically significant finding represents a false-positive result.

The studies used various means of monitoring the treatment efficacy (Q2). These results cannot be directly compared with one another even though the results, which were statistically analyzed, did indicate successful treatment of UUI with MS (Q1). As early as 1998, the International Consultation on Incontinence (ICI) and EAU recommend five domains of interest that should be reported in research studies, including patient observations, quantification of symptoms, clinician observations (anatomical, functional, compliance), QoL, and socioeconomic outcomes. Unfortunately, none of the studies reviewed reported all five domains. However, according to the last report by the EUA, questionnaires should be validated for the language in which they are being used and demonstrated to be sensitive to change [4, 25]. For example, only ICIQ-SF as a patient questionnaire for UI is available as a validated questionnaire in Slovenian, which makes it impossible for smaller countries to equally and objectively participate in measuring outcomes according to the guidelines mentioned above [26]. Moreover, there is no evidence to indicate whether the use of QoL or condition-specific questionnaires has an impact on the outcome of treatment. Therefore, it would be necessary to standardize monitoring of the efficacy of MS treatment for UUI, which would allow direct comparison between studies and define the appropriate time frame for monitoring therapy efficacy (Q5).

Single-arm clinical studies by Doğanay et al. have shown that the effects of MS continued for about a year post-treatment, but efficacy progressively diminished and came close to baseline at the 2nd and 3rd year after treatment [19]. The only RCT included in our review has no follow-up, which makes the long-term efficacy of MS for UI questionable [20].

In reviewing the studies, we found considerable variability in patient characteristics and data collected. The SR of these studies shows that it is necessary to standardize the entry criteria (Q3) and the diagnosis of UUI (Q3).

Further adding to our quandary are the poorly standardized MS protocols. To clarify the impact on the extent of amelioration after therapy with MS, the stimulation parameters should be unified with regard to time frame, impulse intensity, and follow-up tracking. A specific therapy program for different types of UI is usually suggested by producers and based on previous experience. To date, the optimal frequency and pulse duration have not yet been established, although a higher dose of 50 Hz has been reported to be the dose required to achieve good pelvic floor contraction for the treatment of SUI, and a lower dose of 10–20 Hz is required for UUI [5, 11, 13]. Moreover, the number of treatment sessions and session frequency have not been established either, which might be potential confounders contributing to the heterogeneity in studies.

In evaluating the safety of MS, most patients generally tolerated treatment well. However, this safety profile should be interpreted with caution owing to the small sample sizes of the studies included and possible under-reporting of adverse events.

This review has several strengths and weaknesses. No meta-analysis was really performed because the studies were clinically diverse, and therefore a meta-analysis may give biased results and genuine differences in effects may be obscured. A particularly important type of diversity is in the comparisons being made by the primary studies. Furthermore, the lack of a control group can limit the validity of the meta-analysis, and, as mentioned above, only one study (by Yamanishi et al.) was an RCT. For this reason, the results are presented as a narrative review with clinical outcomes. With a comprehensive search strategy, using two main repositories, we ensured that no article on our topic was neglected. We have attempted to systematically and clearly display all outcomes analyzed; however, we did not include studies that analyze the entire spectrum of OAB because we wanted to focus exclusively on UUI. Our SR was designed as a single-arm study, and so we could not compare MS therapy with other therapeutic methods.

We are aware that, considering the lack of studies of consistent RCT data for MS in UUI, further trials are warranted, and a longer follow-up period will provide more evidence to validate the effects of MS treatment. However, taking into account the limitations of our SR, the main results from the studies analyzed confirmed that MS is effective in the treatment of UUI. Another potential limitation of our SR could be that only articles published in English were included.

According to the conclusions in the studies reviewed, MS is a simple form of treatment that can help many UUI patients from the medical, social, and also financial perspective. Because it is non-invasive, it could be used as a treatment approach at the primary level of urogynecological treatment and would thus reduce the number of unnecessary invasive treatments. When adherence to “healthy habits for a healthy bladder” (behavioral therapy) proves ineffective, MS could be the next step in UUI treatment. According to the literature, the MS treatment method does not cause the patient stress because this type of treatment is comfortable, safe, and relatively painless [7, 20].