Objectives: Approximately 17–44% of women diagnosed with endometriosis have ovarian endometriomas (cysts). Although ovarian endometriomas may adversely affect quality of life and work performance, the associations among patient characteristics, cyst size, and pain in women with endometriosis have not yet been reported. Thus, the objective of this study was to assess the association among age, cyst size, and pain in women with ovarian endometriomas. Design: This was a retrospective secondary analysis of pooled data from six randomized clinical trials on the use of low-dose estrogen/progestogen drugs for endometriosis. Participants/Materials, Setting, and Methods: Data on 491 patients enrolled in four randomized and two nonrandomized trials between 2003 and 2017 were pooled. None of the participants had undergone surgical treatment before trial participation. We examined differences in dysmenorrhea score, menstrual pain score, analgesic score, and pelvic pain, as measured using a visual analog scale (VAS), by age and endometrioma size. Results: The mean dysmenorrhea, menstrual pain, and analgesic scores were 4.2, 2.2, and 2.0, respectively. The mean VAS for pelvic pain was 55, which decreased significantly with an increase in age. Age was not associated with endometrioma size, including volume and maximum diameter, or dysmenorrhea score. Additionally, endometrioma volume and maximum diameter were not associated with menstrual pain, analgesic score, or pelvic pain. Limitations: The details of past treatment history were not available; therefore, these could not be considered in the analysis. Additionally, the assessment of pain is heavily influenced by psychological factors, making it difficult to assess the true extent of pain. Conclusions: Endometrioma size was not associated with dysmenorrhea or pelvic pain measured using the VAS.

Journal Section:
Research Article
Keywords:
Dysmenorrhea, Endometriosis, Estrogen/progestogen combined therapy, Ovarian endometrioma, Visual analog scale

Endometriosis is a common gynecological disorder in women of reproductive age that recurs frequently and is characterized by infertility and pain. Endometriosis adversely affects women’s well-being and causes menstrual disorders. In general outpatient settings, quantifying the association between pain and endometriosis may assist with diagnosis and selecting patients who require further imaging.

Ovarian chocolate-like cysts or endometriomas are a major pathological manifestation of endometriosis, occurring in approximately 17–44% of women diagnosed with endometriosis [1]. While ovarian endometriomas may adversely affect quality of life and work performance, to the best of our knowledge, the association between cyst size and the pain in women with ovarian endometriomas has not been elucidated [2]. Therefore, in this retrospective study, we assessed the association between clinical epidemiological background and ovarian endometriomas, focusing on the association among age, ovarian endometrioma size, and pain, using data from patients enrolled in six prospective clinical studies [3‒5].

Data were collected from patients with ovarian endometriomas who participated in studies conducted by Nobelpharma Co., Ltd. to evaluate the efficacy of low-dose estrogen/progestogen combination drugs for endometriosis and its associated symptoms. Results of a literature search were complemented by information provided by the pharmaceutical company. For this study, the data of 952 patients were extracted from four randomized and two nonrandomized trials conducted between 2003 and 2017. Among these, the data of 491 patients with ovarian endometriomas, who had not undergone surgical treatment before participating in the trials, were included in the analysis (shown in Fig. 1).

Fig. 1.
Study flowchart. In this study, 952 patients were pooled from four randomized and two nonrandomized trials. Of these, 491 patients with ovarian endometrioma who had not undergone surgical treatment before participating in the trials were included in the analysis.
View largeDownload slide

Study flowchart. In this study, 952 patients were pooled from four randomized and two nonrandomized trials. Of these, 491 patients with ovarian endometrioma who had not undergone surgical treatment before participating in the trials were included in the analysis.

Fig. 1.
Study flowchart. In this study, 952 patients were pooled from four randomized and two nonrandomized trials. Of these, 491 patients with ovarian endometrioma who had not undergone surgical treatment before participating in the trials were included in the analysis.
View largeDownload slide

Study flowchart. In this study, 952 patients were pooled from four randomized and two nonrandomized trials. Of these, 491 patients with ovarian endometrioma who had not undergone surgical treatment before participating in the trials were included in the analysis.

Close modal

We examined differences by age for the following four items at baseline: dysmenorrhea score, menstrual pain score, analgesic score, and pelvic pain score, as measured using a visual analog scale (VAS). Moreover, we analyzed the correlation among the diameter or volume of ovarian endometriomas and these four items. The size of ovarian endometriomas was classified as greater than or less than or equal to 7.0 cm.

The size (longest diameter and volume) of ovarian endometriomas was examined over time in patients receiving low-dose estrogen/progestogen drugs in four 4-cycle and two 13-cycle trials. In the 4-cycle studies, the second and third cycles of drug administration were considered the intermediate observation period, and the fourth and fifth cycles were considered the final observation period (shown in Fig. 2). The size of ovarian endometriomas during the intermediate and final observation periods was compared with that at baseline. In the 13-cycle studies, the size of endometriomas after 4, 9, 12, and 16 cycles was compared with that at baseline.

Fig. 2.
Schedules and visit timing in the six studies. The dosing schedules and timing of visits for each study are shown. Four studies used 4-cycle regimens and two studies used 13-cycle regimens.
View largeDownload slide

Schedules and visit timing in the six studies. The dosing schedules and timing of visits for each study are shown. Four studies used 4-cycle regimens and two studies used 13-cycle regimens.

Fig. 2.
Schedules and visit timing in the six studies. The dosing schedules and timing of visits for each study are shown. Four studies used 4-cycle regimens and two studies used 13-cycle regimens.
View largeDownload slide

Schedules and visit timing in the six studies. The dosing schedules and timing of visits for each study are shown. Four studies used 4-cycle regimens and two studies used 13-cycle regimens.

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Pearson’s correlation coefficient was used to summarize the correlation between each score and endometrioma size. Differences in endometrioma size and each score (dysmenorrhea, menstrual pain, analgesic, and pelvic pain scores) among the different age groups were evaluated using a one-way analysis of variance. Independent sample t tests were used to further assess differences between age groups.

Paired t tests were used to compare the size of endometriomas at baseline and at each time point. Data are expressed as means ± standard deviations, medians and interquartile ranges, or frequencies and percentages, as appropriate. Data were analyzed using Prism 7.0 (GraphPad Software, San Diego, CA, USA) and R version 3.6.2 for Windows (R Foundation, Vienna, Austria). p values <0.05 were considered significant.

Patient characteristics are shown in Table 1. The median age (range) was 32 (18–49) years, and the median body weight (range) was 52.0 (38.2–89.7) kg. Of the patients, 405 (97.6%) had received previous drug therapy, and 106 (25.5%) had received hormone therapy. The median systolic and diastolic blood pressures were 107 and 65 mm Hg, respectively. The mean dysmenorrhea, menstrual pain, and analgesic scores at baseline were 4.2, 2.2, and 2.0, respectively. The mean VAS score (range) for pelvic pain was 55 (2–100). The analgesic and pelvic pain scores decreased significantly with increasing age (p < 0.01) (shown in Fig. 3a–d).

Table 1.

Patient characteristics

ParameterResponsen = 491
Age, years  32 (18–49) 
Weight, kg  52.0 (38.2–89.7) 
Age at first menstruation, years  12 (8–16) 
Pregnancies, n  0 (0–4) 
Deliveries, n  0 (0–3) 
Past medical history, n (%)  150 (30.5) 
Previous hormone therapy Yes 106 
No 309 
Unknown 76 
Previous medical therapy Yes 405 
No 10 
Unknown 76 
Systolic blood pressure, mm Hg  107 (80–154) 
Diastolic blood pressure, mm Hg  65 (46–93) 
Dysmenorrhea scorea  4.2 (3–6) 
Menstrual pain scorea  2.2 (0–3) 
Analgesic scorea  2.0 (0–3) 
Pelvic pain score (VAS score)a  55.0 (2–100) 
Endometrioma volume, mm3  8.1 (0.2–387.7) 
Endometrioma major axis, mm  28.0 (4–85.4) 
ParameterResponsen = 491
Age, years  32 (18–49) 
Weight, kg  52.0 (38.2–89.7) 
Age at first menstruation, years  12 (8–16) 
Pregnancies, n  0 (0–4) 
Deliveries, n  0 (0–3) 
Past medical history, n (%)  150 (30.5) 
Previous hormone therapy Yes 106 
No 309 
Unknown 76 
Previous medical therapy Yes 405 
No 10 
Unknown 76 
Systolic blood pressure, mm Hg  107 (80–154) 
Diastolic blood pressure, mm Hg  65 (46–93) 
Dysmenorrhea scorea  4.2 (3–6) 
Menstrual pain scorea  2.2 (0–3) 
Analgesic scorea  2.0 (0–3) 
Pelvic pain score (VAS score)a  55.0 (2–100) 
Endometrioma volume, mm3  8.1 (0.2–387.7) 
Endometrioma major axis, mm  28.0 (4–85.4) 

VAS, visual analog scale.

aMean; the other values are presented as the median and interquartile range.

View Large
Fig. 3.
Association between pain scores and endometrioma size at different baseline ages of patients. a Dysmenorrhea score. b Menstrual pain score. c Analgesic score. d Pelvic pain score. The mean dysmenorrhea score was 4.2, the mean menstrual pain score was 2.2, and the mean analgesic score was 2.0. The mean VAS score for pelvic pain was 55. The analgesic and pelvic pain scores decreased significantly with increasing age. e Endometrioma volume. f Endometrioma major axis. Patient age was not correlated with the volume or length of the major axis of the endometrioma at baseline. *p < 0.01.
View largeDownload slide

Association between pain scores and endometrioma size at different baseline ages of patients. a Dysmenorrhea score. b Menstrual pain score. c Analgesic score. d Pelvic pain score. The mean dysmenorrhea score was 4.2, the mean menstrual pain score was 2.2, and the mean analgesic score was 2.0. The mean VAS score for pelvic pain was 55. The analgesic and pelvic pain scores decreased significantly with increasing age. e Endometrioma volume. f Endometrioma major axis. Patient age was not correlated with the volume or length of the major axis of the endometrioma at baseline. *p < 0.01.

Fig. 3.
Association between pain scores and endometrioma size at different baseline ages of patients. a Dysmenorrhea score. b Menstrual pain score. c Analgesic score. d Pelvic pain score. The mean dysmenorrhea score was 4.2, the mean menstrual pain score was 2.2, and the mean analgesic score was 2.0. The mean VAS score for pelvic pain was 55. The analgesic and pelvic pain scores decreased significantly with increasing age. e Endometrioma volume. f Endometrioma major axis. Patient age was not correlated with the volume or length of the major axis of the endometrioma at baseline. *p < 0.01.
View largeDownload slide

Association between pain scores and endometrioma size at different baseline ages of patients. a Dysmenorrhea score. b Menstrual pain score. c Analgesic score. d Pelvic pain score. The mean dysmenorrhea score was 4.2, the mean menstrual pain score was 2.2, and the mean analgesic score was 2.0. The mean VAS score for pelvic pain was 55. The analgesic and pelvic pain scores decreased significantly with increasing age. e Endometrioma volume. f Endometrioma major axis. Patient age was not correlated with the volume or length of the major axis of the endometrioma at baseline. *p < 0.01.

Close modal

The median volume (range) of the ovarian endometrioma measured using ultrasonography or pelvic magnetic resonance imaging was 8.1 (0.2–387.7) mm3, and the median maximum diameter (range) was 28.0 (4–85.4) mm. There was no correlation between patient age and endometrioma size at baseline (shown in Fig. 3e, f).

Dysmenorrhea score was not correlated with endometrioma volume or major axis in any age group (shown in online suppl. Fig. 1; for all online suppl. material, see https://doi.org/10.1159/000534666). Similarly, neither menstrual pain nor analgesic score was correlated with endometrioma volume or major axis (shown in online suppl. Figs. 2, 3). Pelvic pain was not correlated with endometrioma volume or major axis (shown in online suppl. Fig. 4). The major axes and volumes of the ovarian endometriomas in the 4- and 13-cycle studies were reduced following oral drug administration; however, this reduction was not seen in the placebo group (shown in Figs. 4-7).

Fig. 4.
Major axis of ovarian endometrioma according to the drug cycle. Changes in the long diameter of ovarian endometriomas during the four cycles of drug administration. The size of cysts reduced with oral administration of drugs (IKH01-02_G1, IKH01-02_G2, IKH01-04_G3, and NPC-0101_G8). The placebo group (NPC-0102_G10) showed no shrinkage. *p < 0.01; **p < 0.001; ****p < 0.00001.
View largeDownload slide

Major axis of ovarian endometrioma according to the drug cycle. Changes in the long diameter of ovarian endometriomas during the four cycles of drug administration. The size of cysts reduced with oral administration of drugs (IKH01-02_G1, IKH01-02_G2, IKH01-04_G3, and NPC-0101_G8). The placebo group (NPC-0102_G10) showed no shrinkage. *p < 0.01; **p < 0.001; ****p < 0.00001.

Fig. 4.
Major axis of ovarian endometrioma according to the drug cycle. Changes in the long diameter of ovarian endometriomas during the four cycles of drug administration. The size of cysts reduced with oral administration of drugs (IKH01-02_G1, IKH01-02_G2, IKH01-04_G3, and NPC-0101_G8). The placebo group (NPC-0102_G10) showed no shrinkage. *p < 0.01; **p < 0.001; ****p < 0.00001.
View largeDownload slide

Major axis of ovarian endometrioma according to the drug cycle. Changes in the long diameter of ovarian endometriomas during the four cycles of drug administration. The size of cysts reduced with oral administration of drugs (IKH01-02_G1, IKH01-02_G2, IKH01-04_G3, and NPC-0101_G8). The placebo group (NPC-0102_G10) showed no shrinkage. *p < 0.01; **p < 0.001; ****p < 0.00001.

Close modal
Fig. 5.
Volume of ovarian endometrioma according to the drug cycle. Changes in the volume of ovarian endometriomas over the four cycles of drug administration. The size of cysts reduced in the oral administration groups (IKH01-02_G1, IKH01-02_G2, IKH01-04_G3, and NPC-0101_G8). The placebo group (NPC-0102_G10) showed no shrinkage. *p < 0.01; **p < 0.001; ****p < 0.00001.
View largeDownload slide

Volume of ovarian endometrioma according to the drug cycle. Changes in the volume of ovarian endometriomas over the four cycles of drug administration. The size of cysts reduced in the oral administration groups (IKH01-02_G1, IKH01-02_G2, IKH01-04_G3, and NPC-0101_G8). The placebo group (NPC-0102_G10) showed no shrinkage. *p < 0.01; **p < 0.001; ****p < 0.00001.

Fig. 5.
Volume of ovarian endometrioma according to the drug cycle. Changes in the volume of ovarian endometriomas over the four cycles of drug administration. The size of cysts reduced in the oral administration groups (IKH01-02_G1, IKH01-02_G2, IKH01-04_G3, and NPC-0101_G8). The placebo group (NPC-0102_G10) showed no shrinkage. *p < 0.01; **p < 0.001; ****p < 0.00001.
View largeDownload slide

Volume of ovarian endometrioma according to the drug cycle. Changes in the volume of ovarian endometriomas over the four cycles of drug administration. The size of cysts reduced in the oral administration groups (IKH01-02_G1, IKH01-02_G2, IKH01-04_G3, and NPC-0101_G8). The placebo group (NPC-0102_G10) showed no shrinkage. *p < 0.01; **p < 0.001; ****p < 0.00001.

Close modal
Fig. 6.
Major axis of ovarian endometrioma over the 13 cycles of drug administration. Changes in the long diameter of ovarian endometriomas during the 13 cycles of drug administration. The long diameter of ovarian endometriomas decreased in the hormone therapy group, but not in the placebo group. *p < 0.01; **p < 0.001; ***p < 0.0001; ****p < 0.00001.
View largeDownload slide

Major axis of ovarian endometrioma over the 13 cycles of drug administration. Changes in the long diameter of ovarian endometriomas during the 13 cycles of drug administration. The long diameter of ovarian endometriomas decreased in the hormone therapy group, but not in the placebo group. *p < 0.01; **p < 0.001; ***p < 0.0001; ****p < 0.00001.

Fig. 6.
Major axis of ovarian endometrioma over the 13 cycles of drug administration. Changes in the long diameter of ovarian endometriomas during the 13 cycles of drug administration. The long diameter of ovarian endometriomas decreased in the hormone therapy group, but not in the placebo group. *p < 0.01; **p < 0.001; ***p < 0.0001; ****p < 0.00001.
View largeDownload slide

Major axis of ovarian endometrioma over the 13 cycles of drug administration. Changes in the long diameter of ovarian endometriomas during the 13 cycles of drug administration. The long diameter of ovarian endometriomas decreased in the hormone therapy group, but not in the placebo group. *p < 0.01; **p < 0.001; ***p < 0.0001; ****p < 0.00001.

Close modal
Fig. 7.
Volume of ovarian endometrioma over the 13 cycles of drug administration. Changes in the volume of ovarian endometriomas over the 13 cycles of drug administration. The volume of ovarian endometriomas decreased in the hormone therapy group, but not in the placebo group. *p < 0.01; **p < 0.001; ***p < 0.0001; ****p < 0.00001.
View largeDownload slide

Volume of ovarian endometrioma over the 13 cycles of drug administration. Changes in the volume of ovarian endometriomas over the 13 cycles of drug administration. The volume of ovarian endometriomas decreased in the hormone therapy group, but not in the placebo group. *p < 0.01; **p < 0.001; ***p < 0.0001; ****p < 0.00001.

Fig. 7.
Volume of ovarian endometrioma over the 13 cycles of drug administration. Changes in the volume of ovarian endometriomas over the 13 cycles of drug administration. The volume of ovarian endometriomas decreased in the hormone therapy group, but not in the placebo group. *p < 0.01; **p < 0.001; ***p < 0.0001; ****p < 0.00001.
View largeDownload slide

Volume of ovarian endometrioma over the 13 cycles of drug administration. Changes in the volume of ovarian endometriomas over the 13 cycles of drug administration. The volume of ovarian endometriomas decreased in the hormone therapy group, but not in the placebo group. *p < 0.01; **p < 0.001; ***p < 0.0001; ****p < 0.00001.

Close modal

In this study, we examined whether the size of ovarian endometriomas was associated with various pain scores using data extracted from four randomized and two nonrandomized trials. To our knowledge, this is the largest study to date to investigate the association between endometrioma size and pain. Endometrioma size was not associated with dysmenorrhea or pelvic pain VAS scores. The administration of estrogen and progestin agents reduced the size of ovarian endometriomas. Although some studies have found a relationship between pain and endometrioma size, we found no association between them.

As seen in other chronic diseases, endometriosis pain is often associated with psychological distress and fatigue, which may exacerbate pain. Pain threshold has also been reported to increase with age [6], especially the threshold for heat-induced pain, suggesting that pain sensitivity decreases with age [7]. Adolescent women may experience persistent pain; in these cases, we recommend that they be examined for endometriosis and menstruation suppression, until they wish to become pregnant, at which time counseling should be provided [8]. In our study, older women (40–50 years) had significantly lower analgesic and pelvic pain scores than did younger women (20–30 years). Since psychological factors play an important role in pain and reported pain management, it is likely that our results may have been influenced by the psychosocial backgrounds of the patients [9]. Although pain scores decreased with age, we did not observe an association between age and endometrioma size. Moreover, Benagiano and Guo [10] reported that the presentation of endometriosis differs with age, suggesting that the pathophysiology of endometriosis may vary with age and may have an impact on pain.

Few studies have reported on the association between cyst size and pain in patients with ovarian endometriomas. Chmaj-Wierzchowska et al. [11] reported that patients with ovarian endometriomas experience more severe pain than that experienced by patients with teratomas; however, pain was not associated with lesion size but was associated with endometrial tissue components. Their study also revealed that patients with ovarian endometriomas had higher levels of pelvic pain but lower levels of pain-related stress [11]. Furthermore, chemokines and leptin play an important role in causing pain in patients with ovarian endometriomas, and these should be used as therapeutic targets for pain management [12].

Although we did not compare ovarian endometriomas with other tumors or investigate chemokine levels, we did not find an association between pain and endometrioma volume or long diameter, suggesting that ovarian endometriomas do not induce direct pain. Most probably, the pain associated with endometriosis is caused by chemicals generated by ectopic endometrial tissue or adhesions caused by endometriosis. More detailed studies are needed to elucidate these possibilities.

The role of estrogen and progestin agents in reducing the size of ovarian endometriomas remains unclear. However, they may suppress active endometriosis foci and cause size reduction through the absorption of pooled blood. Further research is needed to investigate the efficacy of hormone treatment as it seems to be less effective when treating deep endometriosis and appears to only have a local effect [13].

A strength of our study is the accumulation of accurate data from large clinical trials. Moreover, our study included a large number of cases, which was suitable for statistical analysis. However, there are some limitations. The details of past treatment history were not available, and comorbidities could not be included in this analysis. Additionally, the assessment of pain is heavily influenced by psychological aspects, making it difficult to assess the true extent of pain. Furthermore, we did not analyze revised-American Society for Reproductive Medicine (r-ASRM) scores obtained from surgical findings, as we did not include any patients who had undergone surgery to treat endometriosis. Including r-ASRM scores would have shed light on the mixed effects of adhesions, deep endometriosis, and other causes of pain and should be investigated in the future.

This study used data from six clinical trials to analyze the correlation between endometrioma size and pain. Although pain decreased with an increase in age, there was no clear correlation between endometrioma size and pain. This finding suggests that pelvic pain due to dysmenorrhea is caused by other factors, possibly including psychosocial factors. Estrogen and progestin agents may be effective in reducing the size of ovarian endometriomas.

We would like to express our sincere gratitude to Editage for providing assistance in language correction and writing and for their proofreading services for this manuscript.

This study protocol was reviewed and approved by Tottori University Hospital Research Ethics Committee (approval number 20A119). Written informed consent was obtained from participants to participate in the respective studies.

The authors have no conflicts of interest to declare.

This study was supported by Nobelpharma Co., Ltd., Tokyo, Japan.

H.K., H.N., H.S., and T.H. analyzed and interpreted the patient data. H.K. was a major contributor in writing the manuscript. Y.E. and F.T. reviewed the manuscript to improve this study and provided support for the research. All authors read and approved the final manuscript.

The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.

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