Spontaneous Evolution Endometriosis appears to be a progressive disease in a significant proportion (30% to 60%) of patients. During serial observations, deterioration (47%), improvement (30%), or elimination (23%) was documented over a 6-month period (265,266). In another study, endometriosis progressed in 64%, improved in 27%, and remained unchanged in 9% of patients over 12 months (267). A third study of 24 women reported 29% with disease progression, 29% with disease regression, and 42% with no change over 12 months. Follow-up studies in both baboons and women with spontaneous endometriosis over 24 months demonstrated disease progression in all baboons and in 6 of 7 women (268–270). Several studies reported that subtle lesions and typical implants may represent younger and older types of endometriosis, respectively. In a cross-sectional study, the incidence of subtle lesions decreased with age (271). This finding was confirmed by a 3-year prospective study that reported that the incidence, overall pelvic area involved, and volume of subtle lesions decreased with age, but in typical lesions, these parameters and the depth of infiltration increased with age (6). Remodeling of endometriotic lesions (transition between typical and subtle subtypes) is reported to occur in women and in baboons, indicating that endometriosis is a dynamic condition (272,273). Several studies in women, cynomolgus monkeys, and rodents showed that endometriosis is ameliorated after pregnancy (273–276).
Figure 17.6 Histologic appearance of endometriosis: endometrial glandular epithelium, surrounded by stroma in typical lesion and clear vesicle.
The characteristics of endometriosis are variable during pregnancy, and lesions tend to enlarge during the first trimester but regress thereafter (277). Studies in baboons revealed no change in the number or surface area of endometriosis lesions during the first two trimesters of pregnancy (278). These results do not exclude a beneficial effect that may occur during the third trimester or in the immediate postpartum period. Establishment of a “pseudopregnant state” with exogenously administered estrogen and progestins is based on the belief that symptomatic improvement may result from decidualization of endometrial implants during pregnancy (279). This hypothesis is not substantiated, and it is possible that amenorrhea can explain the beneficial effect of pregnancy and lactation on endometriosis-associated pain symptoms.
Prevention No strategies to prevent endometriosis are uniformly successful. A reduced incidence of endometriosis was reported in women who engaged in aerobic activity from an early age, but the possible protective effect of exercise was not investigated thoroughly (45). There is insufficient evidence that oral contraceptive use offers protection against the development of endometriosis. One report showed an increased risk for endometriosis in a select population of women taking oral contraceptives, possibly explained by the observation that dysmenorrhea as a reason to initiate estroprogestins is significantly more common in women with endometriosis than in women without the disease (280,281). Oral contraceptives (OCs) inhibit ovulation, substantially reduce the volume of menstrual ﬂow, and may interfere with implantation of reﬂuxed endometrial cells, but the hypothesis of recommending OCs for primary prevention of endometriosis is not sufficiently substantiated (282). Although the risk of endometriosis appears reduced during OC use, it is possible that this effect results from postponement of surgical evaluation caused by temporary suppression of pain symptoms (283). Confounding by selection and indication biases may explain the trend toward an increase in risk of endometriosis observed after discontinuation, but further clarification is needed (283).