The purpose of this study is to evaluate the efficacy of an internet-based cognitive behavioral therapy in reducing the impairment caused by endometriosis.

Endometriosis is a chronic disease in which endometrium-like (uterine lining-like) cells settle outside the uterus in the abdomen (Dunselman et al., 2014). The Endometriose Vereinigung Deutschland reports that between eight and 15 percent of all women during reproductive age are affected and that there are 40,000 new cases annually in Germany (Endometriose Vereinigung Deutschland e.V., 2020). Thus, endometriosis is the second most common gynecological disease. Despite the high prevalence, the etiology and pathogenesis of many factors remains unclear. Misdiagnoses are common and to reach the correct diagnosis it takes an average of 5 to 8.9 years (Chaman-Ara, Bahrami & Bahrami, 2017). So far there is no curative treatment option and the primarily medical treatment options are sometimes associated with serious side effects (Moradi, Parker, Sneddon, Lopez & Ellwood, 2014). Endometriosis is characterized by a multitude of physical as well as considerable psychological symptoms that significantly reduce the quality of life of those affected (Gao et al., 2006). For example, endometriosis is associated with higher levels of depression and anxiety disorders (Pope, Sharma, Sharma & Mazmanian, 2015). A psychotherapeutic supplement to the primary medical treatment to promote disease coping and expansion of coping strategies therefore appears sensible.

In the planned study, a CBT program specifically for endometriosis sufferers will therefore be developed and evaluated.

Previous intervention studies aimed at improving the quality of life of endometriosis sufferers examined mind-body interventions such as yoga (Gonçalves, Barros & Bahamondes, 2017), relaxation training (Zhao et al., 2012) and acupuncture in combination with conversational psychotherapy (Meissner et al., 2016). Hansen et al. (2017) were able to show in an uncontrolled pilot study (N = 10) that mindfulness-based psychotherapy significantly reduces the burden of endometriosis. Overall, the number of psychological intervention studies on endometriosis is very low and their quality often requires a critical classification due to methodological limitations (for an overview see Evans, Fernandez, Olive, Payne & Mikocka-Walus, 2019; Van Niekerk, Weaver-Pirie & Matthewson, 2019). Numerous evidence of effectiveness from the area of chronic pain disorders (Williams, Fisher, Hearn & Eccleston, 2020) as well as disorders in the area of women's health such as premenstrual dysphoric disorder (PMDD, Weise et al., 2019) undermine a possible effectiveness of CBT in endometriosis. To the best of our knowledge, however, there is no study to date that has tested the effectiveness of CBT for improving the quality of life of endometriosis sufferers.

The treatment program developed as part of the planned study is to be implemented as an internet-based intervention. A large number of studies confirm the effectiveness of internet-based CBT (iCBT) in various mental (Loughnan, Joubert, Grierson, Andrews & Newby, 2019), psychosomatic (Andersson, Cuijpers, Carlbring, Riper & Hedman, 2014) and somatopsychic diseases (Bernardy, Füber, Köllner & Häuser, 2010). The iCBT has now established itself as being as effective as face-to-face therapy (Carlbring, Andersson, Cuijpers, Riper & Hedman-Lagerlöf, 2018; Andersson, Carlbring & Rozental, 2019)

The internet-based implementation in the present study has various advantages: On the one hand, the effectiveness of the iCBT can be checked efficiently and in a resource-saving manner (Hedman, Andersson, Ljoeétsson, Axelsson & Lekander, 2016). On the other hand, endometriosis sufferers can be addressed throughout the German-speaking area, which ensures that a sufficient sample size can be achieved. Ultimately, those affected that would otherwise not receive any treatment due to the lack of regional availability of interventions, also have access to treatment. In addition, issues such as the desire to have children and endometriosis often lead to shame. An intervention offered online and anonymously can encourage the use of assistance here.

The aim of the study is to examine the effectiveness of iCBT in reducing the stress and impairment caused by endometriosis and in increasing the health-related quality of life.

Inclusion Criteria:

• People with female-assigned reproductive systems aged 18 to 45 years
• Medically confirmed endometriosis diagnosis
• Impairment of quality of life due to endometriosis defined as a value of ≥ 15 points across all scales in the Endometriosis Health Profile 30 + 23 (EHP-30 + 23, (Jones, Kennedy, Barnard, Wong & Jenkinson, 2001a)
• Adequate German language skills
• Access to a personal computer (PC) / laptop and adequate internet connection

Exclusion Criteria:

• Serious mental disorder: unipolar severe depression (Beck Depression Inventory II: raw value ≥ 29), presuicidal syndrome, bipolar affective disorder, unipolar mania, psychotic disorder, alcohol or substance dependence
• Psychotherapeutic treatment: currently or within the last two years
• Use of benzodiazepines (prevents learning processes that are important for psychotherapy)
• Changes in the intake or use (e.g. start / change of dose / discontinuation) of antidepressants and hormonal contraceptives within the last three months
• Current or planned intrauterine insemination (IUI), in-vitro-fertilisation (IVF) or intracytoplasmic sperm injection (ICSI) treatment with hormonal stimulation within the next eight months
• Suffering from one of the following diseases: malignant tumor, in particular breast, cervical or ovarian cancer, ulcerative colitis, Crohn's disease, a known bacterial or viral infection (e.g. tuberculosis (TBC), hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV)
• Current pregnancy or birth of a child within the last six months, breastfeeding within the last six months

Depends on the sample size. Patient data are highly sensible and anonymization might be threatened if the sample size is too small.