The main finding of this study was that the finger-guided transvaginal repeated PNIs provided a significant decrease in VAS scores for both short and long-term periods (two-year follow-up). However, this decrease in VAS scores lost its strength significantly in the 24th month. Another important finding was that the therapeutic PNI was more effective, especially in cases of clinically suspected entrapments of the pudendal nerve between sacrospinous and sacrotuberous ligaments or below (Level-2) when compared with the entrapments in the endopelvic part of the pudendal nerve (Level-1).
PNI is commonly used as a therapeutic procedure in patients with refractory PN when the first-line conservative treatment is failed [6, 15, 19, 28]. According to our study, more than 50% pain reduction was observed in at least half of the patients at each time point. Furthermore, our results showed more than 30% improvement in pain intensity in 91.5% of patients at the 1st month, 82.1% at the 3rd month, 76.8% at the 6th month, 73.2% at the 12th month, and 66.1% at the 24th month. More than 30% pain reduction means a notable improvement for patients who have been suffering from PN for a long time. From our point of view, a series of two PNIs at three-week intervals seems to be highly successful, and significant pain relief or even cure is possible.
In the literature, there are considerable discussions ongoing among researchers concerning the long-term benefits of the PNI. Results from other studies evaluating the effectiveness of pudendal block therapy over time are quite variable, ranging from 6.8 to 89% at 12-month follow-up visits [17, 26, 29]. Fanucci et al.  reported the clinical efficacy of CT-guided repeated PNI in 92% of patients at 12 months. On the contrary, Mamlouk et al.  reported that long-term pain relief was observed in only 2 of the 31 patients (6.6%). They observed that 14 patients' symptoms were improved temporarily after the PNI and benefited from surgical nerve release . Another randomized trial reported that a single dose of PNI was effective for more than 30% in only 14.3% of patients at three months and suggested that anesthetic blockade was necessary to refer patients to surgery . Similarly, in a recent systematic review, Tricard et al.  advocated that the PNI provides short-term benefits; at the same time, nerve decompression surgery, irreversible thermal approaches, sacral nerve, and spinal cord neuromodulation have been suggested to achieve medium as well as long-lasting pain relief. In our opinion, surgery should not be the first option to treat PN because of its invasiveness, and it might leave fibrosis behind, which is another reason for chronic pelvic pain. According to our experiences, pudendal nerve release should be considered a last option of the treatment when minimally invasive therapeutic options (repetitive dose PNI, neuromodulation, and radiofrequency treatment) are exhausted.
Another non-negligible result emerged from this study: despite the significant decrease of VAS pain scores at each time point when compared with the pre-block VAS scores, the effectiveness of the pudendal nerve block significantly declined over time. As expected, the failure rate gradually increased over time (8.5, 17.9, 23.2, 26.8, and 33.9% at one month, three months, six months, one year, and two years, respectively). Accordingly, we thought that the fluctuation of the success rate of the pudendal block therapy might be related to the fact that pain sensation is a subjective phenomenon, resulting in a shift in the patients' pain perceptions among success, relative improvement, and failure over time.
Good knowledge of the endopelvic and extrapelvic course of the pudendal nerve anatomy and adequate surgical experiences is essential to treat PN. While recently published studies focused on the laparoscopic surgical treatment of pudendal pain caused by endopelvic nerve pathologies, on the contrary, our study suggested that PNI might be beneficial in some of the patients who were suspected of having endopelvic pudendal nerve pathology [31, 32]. In the present study, we reported that PNI was more effective when the pathology was between sacrospinous and sacrotuberous ligaments or below compared with the endopelvic pelvic part. Although the success rate of PNI regarding anatomical level in both groups decreased over time, more than 50% pain reduction continued in five patients with pathology at Level-1 and in 24 patients with pathology at Level-2. We should also emphasize that those five patients treated without the need for surgery should not be underestimated. As we reported previously, patients might benefit from surgical decompression of the nerve when there is no adequate response to both conservative therapy and block treatment in patients with persistent PN accompanied by sciatica [12, 33–35]. Laparoscopic exploration of the pelvic nerves allows the clinician to confirm suspected diagnoses, such as deep infiltrating endometriosis, fibrosis of the retroperitoneal space, and entrapment of the pudendal nerve by atypical pudendal vessels or piriformis muscle [11, 36]. However, it is inappropriate to refer all patients to surgery with suspected endopelvic pathology of the pudendal nerve. In our clinical practice, we prefer to perform therapeutic PNIs before deciding a surgery, in case a positive response to a diagnostic block, whether endopelvic or extrapelvic pudendal nerve pathologies are suspected. Patients with endopelvic pathology, who were successfully treated by PNIs, might have double entrapment involving both the endopelvic portion and the distal part of the pudendal nerve. Another explanation for the improvement of VAS scores in patients with pudendal nerve entrapment in the endopelvic part was the choice of injection technique (between sacrospinous and sacrotuberous ligaments). Single site injection between the interligamentous plane seems acceptable, as the sacrospinous ligament level is the most common site of entrapment, and a large volume of injections fills the interligamentous space by spreading the agents to the caudal and cranial.
The main weakness of this study was the absence of a control group, and another limitation was the subjectivity of pain scores and that it could not be standardized. Hence, while the primary outcome of this study was the pain intensity, individual differences were a challenging clinical problem. Thus, we can recommend researchers use the quality-of-life assessment to monitor the improvement of the clinical condition in their further studies to verify our results with control subjects. In addition, it is not possible to determine the exact anatomical level of pudendal nerve insult without surgery. However, based on our experience, physical examination findings can guide clinicians in classifying whether the pudendal nerve injury is endopelvic or extrapelvic. Furthermore, we think that giving patients clear information about the PNI treatment's expected effectiveness might increase the patients' dependence on treatment and follow-up period.
The strengths of our study were the well-established standardization of the patients and long-term post-block follow-up by a senior experienced neuropelveologist. According to these data, the therapeutic pudendal nerve block option should be performed even in patients with suspected endopelvic pudendal nerve pathology before the referral to surgery.
In conclusion, our results suggested that repeated PNIs could provide a significant decrease in VAS scores for both short and long-term periods. However, the efficacy of the pudendal nerve blocks declined over two years. Additionally, the effectiveness of PNIs could also be affected by the anatomical level of the nerve injury. The pudendal nerve entrapment cases between sacrospinous and sacrotuberous ligaments or below benefited more than the cases of pudendal nerve entrapment in the endopelvic part. Therapeutic pudendal nerve injection is recommended even in patients with suspected endopelvic pudendal nerve pathology before the referral to surgery.