What causes a menstrual cramp?

see our new publication: 10.1016/j.ajog.2018.01.035

Am J Obstet Gynecol. 2018 Feb 2. pii: S0002-9378(18)30084-X. doi: 10.1016/j.ajog.2018.01.035. [Epub ahead of print]

Cine MRI during spontaneous cramps in women with menstrual pain.

Hellman KM1, Kuhn CS2, Tu FF3, Dillane KE4, Shlobin NA3, Senapati S3, Zhou X3, Li W5, Prasad PV6.

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Abstract

BACKGROUND:

The lack of noninvasive methods to study dysmenorrhea has resulted in poor understanding of the mechanisms underlying pain, insufficient diagnostic tests, and limited treatment options. To address this knowledge gap, we have developed a magnetic resonance imaging-based strategy for continuously monitoring the uterus in relationship to participants' spontaneous pain perception.

OBJECTIVE:

The study objective was to evaluate whether magnetic resonance imaging can detect real-time changes in myometrial activity during cramping episodes in women with dysmenorrhea, with a handheld squeeze bulb for pain reporting.

STUDY DESIGN:

Sixteen women with dysmenorrhea and 10 healthy control women both on and off their menses were evaluated with magnetic resonance imaging while not taking analgesic medication. Continuous magnetic resonance imaging was acquired using half-Fourier acquisition single-shot turbo spin echo sequence along with simultaneous reporting of pain severity with a squeeze bulb. Pearson's coefficient was used to compare results between reviewers. Proportional differences between women with dysmenorrhea and controls on/off menses were evaluated with a Fisher exact test. The temporal relationships between signal changes were evaluated with Monte Carlo simulations.

RESULTS:

Spontaneous progressive decreases in myometrial signal intensity were more frequently observed in women on their menses than in the absence of pain in the same women off their menses or participants without dysmenorrhea (P < .01). Women without reductions in myometrial signal intensity on their menses either had a history of endometriosis or were not in pain. Observations of myometrial events were consistently reported between 2 raters blinded to menstrual pain or day status (r = 0.97, P < .001). Episodes of cramping occurred either immediately before or 32-70 seconds after myometrial signal change onset (P < .05).

CONCLUSION:

Transient decreases in myometrial uterine T2-weighted signal intensity can be reliably measured in women with menstrual pain. The directionality of signal change and temporal relationship to pain onset suggest that cramping pain may be caused by a combination of uterine pressure and hemodynamic dysfunction.

Copyright © 2018 Elsevier Inc. All rights reserved.

KEYWORDS:

dysmenorrhea; endometriosis; magnetic resonance imaging; pain; uterus