Researchers know what causes endometriosis, but how the cysts that are characteristic of the disease maintain themselves and produce severe pain in some women has remained a mystery.
New research led by Florida State University Professor of Neuroscience Karen Berkley indicates that endometrial cysts develop their own nerve supply that could contribute both to the pain symptoms and the body's ability to maintain the disease.
"The new nerves likely sprout from those that supply the blood vessels that grow along with and nourish the cysts," Berkley said. "It has been well known that the cysts need a blood supply to survive. It also has been well known that blood vessels have their own nerve supply. Surprisingly, no one before us had put the two ideas together - that the cysts would be supplied by nerves that grow and extend from those that supply the cyst's blood vessels."
Berkley and colleagues Natalia Dmitrieva and Kathleen Curtis, both of FSU, and Raymond Papka, of Northeastern Ohio Universities College of Medicine, drew the conclusion after studying rats with surgically induced endometriosis. Their findings will be published in the Proceedings of the National Academy of Sciences journal.
The researchers transplanted small pieces of the rats' uteruses into their abdomens to produce cysts similar to those found in women with endometriosis. When the full-grown cysts were later removed, Berkley and her colleagues found that the cysts had become supplied by two main types of nerves, sensory and sympathetic. The sensory nerves are a type that transmits information about inflammation and injury from the cysts to the central nervous system. These nerves could therefore influence the brain's systems that give rise to bodily perceptions such as pain.
The sympathetic nerves send information from the central nervous system to the cysts. These nerves normally control functions such as blood vessel constriction and thus could influence the cysts' blood supply and growth.
"If what we have seen in rats also occurs in women, what may be the case in women with endometriosis is that some of their abnormal growths develop a direct way to communicate with the brain and for the brain to communicate with the growths," she said. "It's a two-way system of communication with the brain."
The variability of the nerve supply of the growths in different individuals may help explain why symptoms and severity of pain vary so greatly in women who have endometriosis, a disease that may affect up to 50 percent of women in their reproductive years, according to Berkley.
"The symptoms and the severity of the disease are not necessarily correlated, so you can have someone with severe disease and no symptoms, or someone with a lot of symptoms but minimal disease," she said. "That's been a puzzle for years. Knowing that some growths may have a sensory and/or sympathetic nerve supply gives us a new way of thinking about how this variability occurs."
Endometriosis occurs when cells from the lining of the uterus escape into the pelvic cavity, perhaps during menstruation, and attach themselves to the outside of the uterus, ovaries or other organs in the abdomen. The cells can develop into growths or cysts that impact fertility and may cause severe menstrual cramps and other pelvic pains.