Ultrasound and magnetic resonance imaging–based investigation of the role of perfusion and oxygen availability in menstrual pain

Abstract

BackgroundThe mechanisms responsible for menstrual pain are poorly understood. However, dynamic noninvasive pelvic imaging of menstrual pain sufferers could aid in identifying therapeutic targets and in testing novel treatments. ObjectiveTo study the mechanisms responsible for menstrual pain, we analyzed ultrasonographic and complementary functional Magnetic Resonance Imaging (fMRI) parameters in dysmenorrhea sufferers and pain-free controls under multiple conditions. Study DesignWe performed fMRI on participants with and without dysmenorrhea during menses and non-menses. To clarify whether regional changes in oxygen availability and perfusion occur, fMRI R2* measurements were made of the endometrium and myometrium. R2* measurements are calculated nuclear magnetic resonance relaxation rates sensitive to the paramagnetic properties of oxygenated and deoxygenated hemoglobin. We also compared parameters before and after an analgesic dose of naproxen sodium. In addition, we performed similar measurements with Doppler ultrasonography to identify whether changes in uterine arterial velocity occurred during menstrual cramping in real time. Mixed model statistics were performed to account for within-subject effects across conditions. Corrections for multiple comparisons were made with a false discovery rate adjustment. ResultsDuring menstruation, a notable increase in R2* values, indicative of tissue ischemia, was observed in both the myometrium (beta ± standard error of the mean: 15.74 ± 2.29 s-1, p = 0.001, q = 0.002) and the endometrium (26.37 ± 9.33 s-1, p = 0.005, q = 0.008) among participants experiencing dysmenorrhea. A similar increase was noted in the myometrium (28.89 ± 2.85 s-1, p = 0.001, q = 0.002) and endometrium (75.50 ± 2.57 s-1, p = 0.001, q = 0.003) among pain-free controls. Post-hoc analyses revealed that R2* values during menstruation were significantly higher than those in participants with dysmenorrhea (Myometrium: p = 0.008, Endometrium: p = 0.043). Whereas naproxen sodium increased endometrial R2* in participants with dysmenorrhea (48.29 ± 15.78 s-1,p = 0.005, q = 0.008), it decreased myometrial R2*in pain-free controls. Doppler findings were consistent with fMRI (-8.62 ± 3.25 s-1, p = 0.008, q = 0.011). The pulsatility index (-0.42 ± 0.14, p = 0.004, q = 0.004) and resistance index (-0.042 ± 0.012, p = 0.001, q = 0.001) decreased during menses compared with non-menses, and effects were significantly reversed by naproxen sodium. Naproxen sodium had the opposite effect in pain-free controls. There were no significant real-time changes in the pulsatility index, resistance index, peak systolic velocity, or minimum diastolic velocity during episodes of symptomatic menstrual cramping. ConclusionsfMRI and Doppler metrics suggest participants with dysmenorrhea have better perfusion and oxygen availability than pain-free controls. Naproxen sodium's therapeutic mechanism is associated with relative reductions in uterine perfusion and oxygen availability. An opposite pharmacological effect was observed in pain-free controls. During menstrual cramping, there is insufficient evidence of episodic impaired uterine perfusion. Thus, prostaglandins may have protective vasoconstrictive effects in pain-free controls and opposite effects among participants with dysmenorrhea.