CHAPEL HILL -- Women with a very severe form of premenstrual syndrome are more sensitive to pain and are more likely to have lower blood levels of beta-endorphins, the body's natural pain-killing hormones.
The new findings come from a study headed by Susan S. Girdler, Ph.D., assistant professor of psychiatry at the University of North Carolina at Chapel Hill School of Medicine. They apply to women diagnosed with premenstrual dysphoric disorder (PMDD). The research will be presented for the first time at the American Psychosomatic Society Annual Meeting held March 1-4 in Savannah, Georgia.
PMDD affects five to ten percent of women in their childbearing years. Its hallmarks include severe depression, irritability and/or anxiety during the second half of the menstrual cycle. Physical pain is also a major component of this psychiatric disorder.
One preliminary study suggested that women with PMDD have increased pain sensitivity three to seven days before menstruation. It is during this "luteal" phase of the menstrual cycle that the uterus prepares itself for implantation of the egg. Girdler's new study extended previous findings by testing women during both the luteal and earlier "follicular" phase of the cycle, while the egg is in the ovary, a time typically not associated with PMDD symptoms.
"We wanted to see if there are differences in pain sensitivity in PMDD women compared to women without the disorder," said study co-author Patricia A. Straneva, a Ph.D. candidate in psychology at UNC-CH. "We hypothesized that differences in pain sensitivity would be due to altered beta-endorphins. If we found it in both phases of the cycle, it would tie in nicely with earlier work by Dr. Girdler and others who have found abnormal neuroendocrine levels all month long in PMDD women."
In previous studies of women with PMDD, Girdler and her UNC colleagues found abnormalities throughout the monthly cycle in hormones related to stress -- cortisol and norepinephrine.
"We saw evidence that their stress response systems are dysregulated," Girdler said. "Measures of norepinephrine were abnormally elevated in PMDD women, while their cortisol levels were abnormally low. And we saw this regardless of what day of the cycle we looked at."
The new study compared 27 women who met stringent psychiatric criteria for PMDD with 27 age-matched "controls" for pain sensitivity and beta-endorphin levels in both cycle phases. All participants were physically healthy and not taking any psychiatric medication or oral contraceptives. Blood tests during the study confirmed that each woman was ovulating. Beta-endorphin levels were measured by blood samples taken at baseline and during pain testing. A standard blood pressure cuff inflated to 200 mmHg while the subject was asked to open and close her fist induced ischemic arm pain caused by constriction of blood flow. During this pain test, time to pain onset and voluntary tolerance were assessed and subjects were asked to numerically rate the intensity of pain and how unpleasant they found it to be.
In both menstrual phases, results revealed that PMDD women were more sensitive to pain and found the experience more painful compared to the control women. PMDD women had significantly lower pain threshold times and lower tolerance times in both menstrual phases. Moreover, their beta-endorphin levels also were significantly lower during both cycles at rest and during pain testing.
While other studies have documented lower plasma beta-endorphin levels in PMDD, this is the first study to investigate the relationship between beta-endorphins and behavioral indices of pain in PMDD. "Our findings suggest that alterations in the endogenous opioids, specifically beta-endorphins, may contribute to the significant physical distress that PMDD women also experience each month," Girdler said.
"These and earlier findings leads us to re-conceptualize PMDD as a disorder with a biological basis that lasts across the menstrual cycle and not just something that occurs in the very late luteal phase," Straneva said.
Note to media: Contact Patricia Straneva and Dr. Susan Girdler at 919-966-2544; email: stranepa@med.unc.edu UNC School of Medicine Contact: Leslie Lang, 919-843-9687; email: llang@med.unc.edu