Biases in the endometriosis literature: Illustrated by 20 years of endometriosis research in Leuven

Abstract

Aim: To review the Leuven data on endometriosis to demonstrate the shifts that occurred over the years in diagnosis of endometriosis, classification of women with endometriosis and thus in interpretation of results. Results: The contributions to the LUF syndrome, to non-pigmented endometriosis, to cystic ovarian endometriosis, to deep endometriosis, to endometriosis as an immunologic disease and to the development of an animal model of endometriosis, illustrate the persistent interest in endometriosis over 20 years. Using these data it can be shown how progressively the recognition of endometriosis caused important shifts from women who in the beginning of this period were classified as normal, to women who later became classified as having minimal or mild endometriosis. This was caused initially by the active search for small typical lesions and later by the recognition of non-pigmented lesions as endometriosis. The second important shift was caused by the recognition that deep endometriosis is not only a frequent disease, but that these women are predominantly classified as having mild to moderate endometriosis and even as women without endometriosis. The third shift is still ongoing, since the deep lesions reported become progressively smaller, by the “enthusiasm” of the surgeons, and by the introduction of a menstrual clinical exam. A fourth bias in the literature concerns the diagnosis and treatment of cystic ovarian endometriosis. Together with these shifts in recognition and treatment of endometriosis, our understanding of the physiopathology of endometriosis has changed. This is illustrated by the new concepts which have emerged over this period. These are, the focal treatment of cystic ovarian endometriosis, the concept that mild endometriosis could be a normal physiological condition and the endometriotic disease theory. Conclusion: To interpret the data of the literature we should be aware of the shifts that have occurred in the classification of endometriosis over the past 20 years, and which still can hamper the comparison of results between research groups.