CPP is not currently an approved US Food and Drug Administration (FDA) indication for SNM. There is emerging data showing that SNM is effective in the treatment of CPP with multifactorial etiology (2, 3, 11). There are only a few studies showing good short-term results of SNM in the treatment of endometriosis related CPP (8–10), but long-term data is lacking. This Finnish national study is the first to show promising long-term results in the difficult to treat group of endometriosis patients with CPP after surgery.
The long-term efficacy of SNM in our study is reflected by the fact that 71% of the patients that received the IPG had a functioning device by the end of the follow-up and this is better than the reported SNM long-term outcomes with different etiologies (12). It is also illustrated by the decrease of the pain related NRS value from a median of 7.4 (3.6–10) before SNM to 2.25 (0-6.5) by the time of follow-up.
The complication rates are comparable with those reported in earlier studies (2, 13). The overall implantation rate of 88% in our study is better than the implantation rate of 64.3% reported by a recent meta-analysis and systematic review of SNM in CPP, with a quite diverse etiology of pain (2). The implantation rate is also better than the one of 54,8% reported by another meta-analysis and systematic review of SNM in CPP (3).
CPP affects women’s quality of life deeply. CPP is often associated with migraine and headache, regardless if CPP is related or not to endometriosis (14). Endometriosis and CPP was reported to negatively impact all domains of life including physical, psychological, social, sexual, education and employment (15). A large multi-center study across Europe, UK and the USA found that the total cost per woman with endometriosis per year was €9579 with the bulk of costs (€6298) being due to absence from work (16). It has been shown that as little as a 10% reduction on a pain scale is needed to improve productivity (17).
All the patients in our study underwent standard medical therapy and at least one surgery for endometriosis before SNM. According to literature, surgery does not reduce pain in 20–28% of patients (18). Post-surgical hormonal therapy has been advocated to improve the effectiveness of surgery and prevent recurrences, but it has been proven to be of limited or no benefit for endometriosis in general and for deep peritoneal endometriosis in particular (19). Given the amount of non-responders to surgery and the recurrence of pain, even though there is no evident recurrence of endometriosis in 23%, there is a need for evidence-based approaches that do not require surgery or taking hormones (15). Diet, exercise, physiotherapy, acupuncture, psychotherapy could be considered (15) and this is the area where SNM might play a role. It was suggested that a major contributing factor for endometriosis-associated pain are not the ectopic growths themselves, but rather the activity from nerves that have emerged from nearby tissues to innervate the growths, which affects the activity of neurons in the spinal cord and brain (20). This could explain why SNM is effective. Our study encourages the use of SNM in endometriosis patients with CPP post-surgery, regardless of the type of endometriosis or the extent of surgery performed.
This study has a few limitations. This is a retrospective study. The total number of the patients is relatively small, but on the other hand this is a comprehensive national study including all the patients that underwent SNM therapy for endometriosis-associated CPP between 2004 and 2017. More studies are definitely needed in order to standardize the role of SNM in the treatment of endometriosis patients with persisting CPP after surgery.