Endometriosis is a gynecologic disease caused by endometrial tissue growing outside the uterus resulting in an inflammatory state in the affected area related to estrogenic stimulus [1,2]. An estimated 10% of women in their childbearing age suffer from the disease [3-4] and, most of them with symptoms that reduce their quality of life (QoL). Pelvic pain, usually associated with menstruation (dysmenorrhea), is the main symptom. However, dysmenorrhea can be triggered or may become worse during sexual intercourse (dyspareunia), regardless of the menstrual cycle. Besides, there is an increased risk of infertility [5-9], and psycho-emotional alterations associated to endometriosis [10-16], that together with dyspareunia, may affects not only women's sexual health but also to their partners [17-18], generating a feeling of guilt and low self-esteem [19,20].

Human sexuality is a complex phenomenon driven by hormonal, psychological and social factors [21] and it´s a major determinant of QoL [22]. The Female Sexual Function Index (FSFI), which has been validated in Spanish [23], can be used to assess sexual health in women. This questionnaire consists of 19 close-ended questions related to desire, arousal, lubrication, orgasm, satisfaction and pain, which are the 6 domains of sexuality [23].

This study aims to analyze the role of endometriosis in women's sexual health using the FSFI questionnaire, comparing scores of a group of patients with endometriosis relative to a control group disease-free. Secondarily, the influence of hormonal endometriosis treatment on the patient's sexual health was evaluated.

This research indicates the impact of endometriosis on women's sex lives by comparing women with endometriosis and healthy women. It also provides information to health professionals about the most appropriate treatment option by comparing patients with endometriosis taking treatment or not taking treatment and comparing two types of treatment (Dienogest and combined treatment). In addition, it is observed which sexual domain is most affected, so that patients can be better addressed. By carrying out this type of study, it is clear that there is a large population suffering from this type of disease and it is a way of giving it greater visibility. This research can serve as a pilot study for future research, as the sample is small.

In order to compare sexual health of women with and without endometriosis, a case-control study was designed. A total of 22 patients with endometriosis (EG) and 22 patients without endometriosis (CG) completed the questionnaire and were included in the study. Patients that did not complete the whole questionnaire were excluded from the study. The inclusion criteria were patients aged between 18 and 45, with an ultrasound diagnosis of endometriosis. The exclusion criteria were patients who received endometriosis surgery, medical treatment for endometriosis lasting less than 6 months, presence of prolapse, psychiatric problems or an ongoing oncologic process.

Patients with suspected endometriosis were referred to the endometriosis clinic of the University Hospital Virgen de la Victoria or to the clinic Centro AIMA, both located in Malaga, Spain. All of them underwent a specific anamnesis, examination and ultrasound, following the protocol described by the IDEA working group [24]. All patients were studied by the same gynecologist specialized in the disease, expert and specifically trained in endometriosis ultrasound. Patients with endometriosis were classified according to whether or not they were taking hormonal treatment for the disease and the kind of drug, distinguishing between Dienogest 2 mg/24 h in a continuous regimen or combined estrogen and Gestagen contraceptives in a cyclic regimen.

All participating patients in both groups received the FSFI questionnaire in order to measure their sexual function. The questionnaire consists of 19 questions on the 6 domains of sexuality (desire, arousal, lubrication, orgasm, satisfaction and pain) during sexual activity, vaginal intercourse and sexual stimulation. The maximum possible score was 36 points (best sexual function), and the minimum was 2 points (poor sexual function).

An analysis of the sample distribution was made using the Kolmogorov-Smirnov test (KS-test). Two methods of analysis were used to make the intragroup and intergroup comparison. The Student's t-test was used for the variables that were parametric in the KS-test. For the non-parametric variables, the Wilcoxon signed-rank test was used.

Data were analyzed from a descriptive point of view. The results were compared using the Statistical Package for the Social Sciences or SPSS (23.0 Windows version, Illinois, USA). The significance level was established for values of p<0.05.

Final FSFI questionnaire mean score was higher in the group of patients without endometriosis (26.409 vs. 23.695), without being statistically significant (P=0.622) (Table 1).

Patients without endometriosis scored higher on average in all sexuality domains, with a statistically significant difference in the desire section (P=0.016) (Table 1).

In terms of treatment, those who did not receive hormonal treatment obtained a higher final FSFI score than those who did (25.015 vs. 21.789), (P=0.012). Although they had higher scores in all the domains of the questionnaire, the differences were especially significant in the lubrication domain (P=0.006) (Table 2). As for the type of treatment, there were no significant differences between Dienogest in a continuous regimen and combined contraceptives in a cyclic regimen (Table 3).

In this study we wanted to find out how endometriosis affects the quality of sexual life of women who suffer from this disease.

Currently, 10% of women of childbearing age suffer from this disease and the symptoms affect their quality of life. More education and an effective treatment protocol are therefore needed.

The study by Yang et al. [25] compared the FSFI questionnaire scores of women with endometriosis and healthy women and obtained better results in patients without endometriosis with significant differences in three domains of sexuality, which were arousal, pain, and satisfaction. In research by Evangelista et al. [26] and Cozzolino et al. [27] also compared the FSFI questionnaire score between patients with deep endometriosis and healthy patients and both obtained no significant differences in the total score. Evangelista et al. [26] report significant differences only in the pain domain. Cozzolino et al. [27] indicate that patients with total or partial infiltration of the rectovaginal septum have a poorer quality of sexual life. Our study agrees with the results obtained in the research by Evangelita et al. [26] and Cozzolino et al.  [27], as our data also indicate that there were no significant differences between the two groups, although it does not coincide with the domain in which significant differences were obtained.

Caruso et al. [28] carried out two studies on whether Dienogest reduced pain caused by endometriosis. In both cases, pain was reduced after taking them for 6 months. These studies have similar conclusions to the data we have obtained, as when comparing patients taking treatment and not taking treatment, better results were obtained in patients taking the treatment, although the difference was not significant. This means that those patients taking treatment, having fewer symptoms, have a better quality of sexual life.

This study has several limitations, which are: (1) The sample size (n = 44) is small due to the fact that the research was conducted in 5 months (from June 2023 to October 2023, both months inclusive) and did not allow time to recruit more patients. In addition, 6 patients were excluded for incorrectly completing the FSFI questionnaire, which also made the sample even smaller. (2) We did not differentiate between types of endometriosis (superficial and deep) because initially this was taken into account, but the number of patients with each type of endometriosis was very unequal, so the statistical data obtained would not be reliable, so we did not take this part into account and only took into account the disease itself. Bearing in mind these two limitations, this research could be used as a pilot study for a more extensive investigation in the future, in which it would be possible to differentiate how superficial and deep endometriosis affect the quality of sexual life of women.

Endometriosis is a highly prevalent, chronic and recurrent disease whose associated symptoms can interfere with women's quality of life.

Scientific interest in this pathology has increased in recent years, allowing the development of drugs and surgical protocols to fight inflammation and pain. However, little is known about the impact of the disease on other aspects that affect the perception of health, including sexuality. Dyspareunia, infertility and associated psychological disorders could affect it negatively.

Sexual penetration can lead to inflammation and pain due to direct stimulation of the endometriotic implants. Furthermore, if pain is recurrent, it can lead to chronification by activation of peripheral and central sensitization processes. This will eventually result in vaginismus, vulvodynia or myofascial syndrome. As a result, there is a greater rejection of sexual intercourse, activating a feedback loop to dyspareunia, chronic pelvic pain, and sexual dysfunction.

In addition, considering the reproductive purpose, fertility problems will also have a negative influence, with feelings of frustration and conflict in the relationship.

In the present study it is observed that endometriosis does indeed play a negative role in sexual desire. Although in the rest of the domains of sexuality there were no significant differences, the scores suggest a tendency towards better sexual health in patients without the disease. A comparison with a larger sample of patients would be interesting.

In terms of treatment, hormonal drugs had a negative influence on sexual health in general, with a particular difference in the lubrication domain scores. There were no differences between the type of hormonal treatment received (Dienogest or combined contraceptives).

It is assumed that in the case of a patient with endometriosis the main effort should be focused on reducing the disease and treating the pain it generates. However, it must be taken into account that it is not only the lesion that is being treated, but the person who suffers from it, and that sexuality represents an important component in the perception of quality of life in women. Therefore, knowing and predicting the influence of endometriosis on female sexual health can be of great help in improving patient care.