Evaluating Subtypes of Endometriosis in Rhesus Macaques (Macaca mulatta) Using Clinical Findings and...

Endometriosis is defined as endometrial tissue outside of the uterus. It is a debilitating, complex, and underdiagnosed condition, impacting approximately 10%-15% of reproductive-aged women worldwide. Endometriosis is associated with chronic pain, infertility, diminished well-being from invasive and delayed diagnostics, and limited treatment options. It is reported to cause approximately 23,000 hospitalizations and cost approximately $9 billion annually due to reduced quality of life and productivity. Endometriosis also occurs spontaneously in rhesus macaques (Macaca mulatta), and similar negative impacts are seen in research colonies. Despite extensive research in both species, much remains unknown about its etiopathogenesis, especially regarding uncommon presentations. This retrospective observational cohort study evaluated clinical findings from 68 rhesus macaques diagnosed with endometriosis at the Emory National Primate Research Center and characteristics associated with their endometriosis lesions. Animals were categorized into 4 endometriosis subtypes: pelvic, abdominal, extra-abdominal, and invasive. Prevalence and descriptive statistics were calculated for reproductive history, physical exam findings, and other observations related to an endometriosis diagnosis. In addition, immunohistochemical analysis was performed on lesions from a subset of 27 macaques and 6 controls to evaluate variation in mean staining intensity and distribution (±SEM) for estrogen receptor α (ERα), progesterone receptor (PR), and CD10 antibodies. Clinical data corroborated established literature by demonstrating common findings associated with endometriosis. It provided novel information by examining the relationship and patterns of these findings in uncommon presentations of endometriosis. Analysis of mean staining intensities (±SEM) revealed significant differential expression of ERα and PR in abdominal endometriosis compared with extra-abdominal and invasive subtypes, as well as autologous eutopic uterine tissue. This study provides important data that may begin to unravel some of the underlying mechanisms by which endometriosis behaves in varied ways.