Pathophysiology of endometriosis-associated pain: A review of pelvic and central nervous system mechanisms.

Although pain is one of the main symptoms women with endometriosis present with, there is poor correlation between symptom severity and disease burden and the underlying biological mechanisms by which pain arises are still only poorly understood. We briefly review the neurobiology of pain before considering mechanisms that may be specifically relevant in the context of endometriosis. The role of pelvic factors such as new nerve fibre growth, peritoneal fluid and inflammation is explored with a particular focus on studies where these factors have been associated with pain symptoms rather than just being compared between women with endometriosis and disease-free controls. We then consider the role of the central nervous system and associated systems, including the stress axis and psychological factors, in the modulation of pain. The potential for changes in these systems to be a cause and/or a consequence of the pain and how they might explain some of the known associations between endometriosis and other somatic symptoms is discussed. The chapter concludes by considering the implications of these mechanisms on treatment strategies for these women.