Classification of Endometriosis

Although recognized as a disease process since the early part of the twentieth century, endometriosis remains an enigmatic disease. Attempts at classification of a disease for which the etiology, pathophysiology, and natural history are still subject to much debate have, not surprisingly, resulted in classification schemes that have shortcomings. Ideally, a classification system should allow for an accurate assessment of a disease state with respect to extent, location, and perhaps nature of disease; this would allow clear communication among those who treat the disease. Moreover, an ideal classification should also be useful in the prediction of outcome based on stages of disease that should behave similarly. Additionally, classification schemes should be such that similar disease stages have similar, predictable outcomes in response to treatment. Therefore, a classification system should not only point to an accurate prognosis but also guide the choice of treatment. There is growing recognition that the current classification system for endometriosis does not fulfill these criteria. There are several sources of potential errors. Our current knowledge of the disease process influences our diagnostic methods and ability to address accurately the basic tenets of a classification scheme. For instance, there is evidence that endometriosis may have many different appearances, 16 , 26 which may increase the potential for observation error. It is also difficult to design a classification system based on stage of disease in which the natural history of the disease is still poorly understood. Additionally, use of a scoring system with arbitrary weights and breakpoints to define clinical stages based on clinical opinion rather than empiric estimates has led to weak relationships between the classification score and measured outcome variables. 20 , 35 , 43 Thus, the ideal classification for endometriosis has not yet been achieved. This article presents the historical evolution of the classification of endometriosis and reviews the limitations of the current revised American Fertility Society classification, with respect to both infertility and pain.