Although it has been more than 100 years since endometriosis was first described in the literature, deciphering the mechanisms that cause pain in women with this enigmatic disease is an ongoing pursuit.
Pain is the most debilitating symptom of endometriosis.1,2 In many cases, it has a profoundly negative impact on a patient’s quality of life, and contributes significantly to disease burden, as well as to personal and societal costs from lost productivity.3,4 Women with endometriosis often experience chronic pelvic pain, deep dyspareunia, dysmenorrhea, and subfertility.5 The majority of women with the disease also have one or more comorbidities, including adenomyosis, adhesive disease, and other pelvic pain conditions such as interstitial cystitis, irritable bowel disease, inflammatory bowel disease, and pelvic floor myalgia.6-8
Recent studies have yielded new insights into the development of endometriosis-associated pelvic pain. The role of peritoneal inflammation, de novo innervation of endometriosis implants, and changes in the central nervous system are becoming increasingly clear.5,9,10 These discoveries have important treatment implications.
In this article, Andrea J. Rapkin, MD, Professor of Obstetrics and Gynecology at the University of California, Los Angeles, and Founder and Director of the UCLA Pelvic Pain Center, offers her expert opinion on the findings of key studies and their clinical implications, including the importance of a multidisciplinary treatment approach that focuses on the whole patient.
Q What mechanisms underlie the chronic pain that many women with endometriosis feel?
Although pain is the primary symptom experienced by women with endometriosis, the disease burden and symptom severity do not often correlate.11,12 “This was the first conundrum presented to clinicians,” noted Dr. Rapkin. “In fact, we do not know the true prevalence of endometriosis because women with endometriosis only come to diagnosis either based on pain or infertility. When infertility is the problem, very often we are surprised by how much disease is present in an individual with either no pain or minimal pain. Conversely, in other individuals with very severe pain, upon laparoscopic surgery, have minimal or mild endometriosis.”
Efforts to solve this clinical puzzle began decades ago. “Dr. Michael Vernon discovered that the small, red, endometriosis implants that looked like petechial hemorrhages produced more prostaglandin E2 (PGE2) in vitro than the older black-brown lesions. PGE2 is a pain-producing (algesic) chemical produced after cytokines stimulation,” said Dr. Rapkin. “This was the first evidence that, yes, there is a reason for pain in many individuals with lower-stage disease.”
“Prostaglandins are known to be a major cause of dysmenorrhea. Prostaglandins induce uterine cramping, sensitize nerve endings, and promote other inflammatory factors responsible for attracting monocytes that become macrophages, further contributing to inflammation,” Dr. Rapkin continued. “PGE2 also stimulates the enzyme aromatase, which allows androgens to be converted to estrogen, which promotes growth of endometriotic lesions. This is a self-feeding aspect of endometriosis.”
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