Endometriosis patients with thyroid dysfunction may have increased risk of more intense chronic pain and increased disease severity, a study suggests.

The underlying disease mechanism of endometriosis is still unclear.

Autoimmune thyroid disorders are associated with endometriosis, but the mechanism by which the two diseases are linked is unknown.

Each cell in the body carries protein markers called antigens that allow a cell to be identified as “self” or “non-self” by the immune system. In autoimmune thyroid disorders, the body’s own immune system attacks and damages the thyroid gland. These diseases are characterized by the production of autoantibodies against thyroid-specific antigens, including the thyroid itself and the thyroid-stimulating hormone receptor.

Now, researchers at the Université Paris Descartes looked at the relationship between endometriosis and autoimmune thyroid disorders, specifically at how thyroid disorders affect the progression of endometriosis.

They first found that both the levels of RNA and proteins involved in thyroid metabolism were altered in the biopsied endometrium of patients with endometriosis compared to healthy people. RNA molecules act as templates to make proteins, which perform key functions in the cell.

Moreover, in endometriotic cells, the amount of thyroid hormones was altered compared to that of control cells. The thyroid hormone T4 (thyroxine) is converted into T3 (triiodothyronine), which is much more active than T4. In the endometriotic cells, T4 production was increased while that of T3 was reduced.

The thyroid-stimulating hormone regulates the production of T3 and T4. In vitro (lab) studies using cells from the endometrium of endometriotic patients and healthy controls showed that thyroid-stimulating hormone increased cells’ proliferation. But the researchers saw no differences in the increase of proliferation rate between endometriotic cells and control cells.

Mouse studies confirmed the data gained in vitro since endometriotic implants were found to be bigger when thyroid hormones increased. A retrospective analysis of endometriosis patients with or without a thyroid disorder revealed an increased chronic pelvic pain and disease score in endometriotic patients with a thyroid disorder.

The study, “Role of thyroid dysimmunity and thyroid hormones in endometriosis” was published in the journal PNAS

Read more: https://www.pnas.org/content/116/24/11894