Zusammenfassung

BACKGROUND: Dysmenorrhea is a pervasive pain condition that affects 20–50% of reproductive-aged women. Distension of a visceral organ, such as the uterus, could elicit a viscero-motor reflex resulting in involuntary skeletal muscle activity and referred pain. Although referred abdominal pain mechanisms can contribute to visceral pain, the role of abdominal muscle activity has not yet been investigated within the context of menstrual pain. OBJECTIVE: The goal of this study is to determine if involuntary abdominal muscle activity precedes spontaneous episodes of menstrual cramping pain in dysmenorrheic women and if naproxen administration affects abdominal muscle activity. STUDY DESIGN: Abdominal electromyography activity was recorded from women with severe dysmenorrheic (n=38) and healthy controls (n=10) during menses. Simultaneously, pain was measured in real-time using a squeeze-bulb or visual analog rheostat. Ninety minutes after naproxen administration, abdominal electromyography activity and menstrual pain were re-assessed. As an additional control, women were also recorded off-menses and data were analyzed in relation to random bulb squeezes. Since it is unknown whether mechanisms of menstrual cramps are different in primary or secondary dysmenorrhea/chronic pelvic pain, the relationship between medical history and abdominal muscle activity was examined. To further examine differences in nociceptive mechanisms, pressure pain thresholds were also measured to evaluate changes in widespread pain sensitivity. RESULTS: Abdominal muscle activity related to random-bulb squeezing was rarely observed in healthy controls on menses (0.9 ±0.6 episodes / hour) and in dysmenorrhea participants off menses (2.3 ± 0.6 episodes / hour). In dysmenorrheic participants during menses, abdominal muscle activity was frequently associated with bulb-squeezing indicative of menstrual cramping pain (10.8 ± 3.0 episodes / hour; p <0.004). Whereas 45% (17/38) of the women with dysmenorrhea had episodes of abdominal muscle activity ...