The effect of the levonorgestrel-releasing intrauterine system, Mirena® on mast cell numbers in women with endometriosis undergoing symptomatic treatment.

OBJECTIVES

Mirena® has been shown to improve symptoms in women with minimal to moderate endometriosis. The precise mechanisms for this have not been thoroughly investigated. We investigate here one possible mechanism-alteration in the number of mast cells in the endometriotic tissue.

STUDY DESIGN

Tissues (endometrial, endometriotic and normal peritoneal biopsies) prospectively collected from twenty-eight women with laparoscopically confirmed minimal to moderate endometriosis before and 6 months after treatment with Mirena® were processed for immunohistochemistry for ER and PR expression followed by toluidine blue staining for mast cells. Photographs were obtained and the receptors and mast cells identified and quantified.

RESULTS

The mean (± SEM) age of the twenty-eight women was 31 (±7.2) (range 18-42) years. Eight of the endometrial biopsies were in the proliferative phase and twenty in the secretory phase. Six months after Mirena®, the number of mast cell expressed in the tissues decreased significantly in the eutopic (P=0.0358) and ectopic endometrium (P=0.0220) but not in the normal peritoneum (P>0.05). There were no ERs or PRs found in mast cells.

CONCLUSION

Mirena® causes a reduction in mast cell numbers in ectopic and eutopic endometrium in women undergoing symptomatic treatment of minimal to moderate endometriosis. This reduction could partly explain the efficacy of Mirena® in modulating pain in these women.