The postulated mechanisms for the generation of pain from pelvic structures in primary dysmenorrhea are summarized in Figure 4. The increased uterine production and release of prostaglandins at menstruation give rise to increased abnormal uterine activity, which then causes uterine hypoxia and pain. Increased uterine activity and uterine ischemia or hypoxia are two major factors in the causation of the pain. Prostaglandins, such as prostaglandin E2, and cyclic endoperoxides hypersensitize pain fibers in the pelvis and uterus to the action of pain-inducing substances or factors. This understanding of the pathophysiology of primary dysmenorrhea has enabled the rational use of nonsteroidal antiinflammatory drugs for the relief of primary dysmenorrhea rather than pharmacotherapy, which merely inhibits uterine contractions, such as with betamimetic agents.
Fig. 4. Mechanism of pain generation from the pelvic structure in primary dysmenorrhea.(Dawood MY: Hormones, prostaglandins, and dysmenorrhea. In Dawood MY [ed]: Dysmenorrhea, p 21. Baltimore: Williams & Wilkins, 1981.)