Psychological characteristics and structural brain changes in women with endometriosis and endometriosis-independent chronic pelvic pain.

Abstract

Study question: Are there neurobiological changes induced by endometriosis?

Summary answer: Women with endometriosis demonstrate specific neurobiological changes distinct from those in patients with chronic pelvic pain (CPP) in the absence of endometriosis.

What is known already: Endometriosis is a chronic disease affecting women of reproductive age that presents with pain and infertility often accompanied by comorbid mental disorders. Only one study with a number of limitations has investigated changes in gray matter volumes and functional connectivity in a small group of patients with endometriosis.

Study design, size, duration: This prospective study recruited 53 women undergoing a laparoscopy due to suspicion of symptomatic endometriosis and 25 healthy, pain-free women. Clinical and psychological characteristics, thermal pain perception, and voxel- and surface-based morphology were assessed in all study participants. Thereafter, the patients underwent a laparoscopy, where endometriosis was either histologically confirmed and removed, or ruled out. Correspondingly, patients were assigned into the group with endometriosis (n = 27) or with endometriosis-independent CPP (n = 26) and compared to the pain-free controls.

Participants/materials, setting, methods: The study groups were generally representative for the population of women with endometriosis. Sociodemographic, medical, clinical, and psychological characteristics were collected using various questionnaires and a structured clinical interview. Thermal pain perception and voxel- and surface-based morphometry were assessed using thermode and MRI, respectively.

Main results and the role of chance: Despite comparable pain intensity and burden of mental disorders, both patient groups demonstrated distinct neurobiological patterns. Women with endometriosis exhibited increased gray matter volume (GMV) in the left cerebellum, lingual gyrus and calcarine gyrus, compared to those with endometriosis-independent CPP. Patients with CPP had decreased GMV in the right cerebellum as compared to controls. Dysmenorrhoea severity correlated positively with GMV in the left inferior parietal lobule, whereas depressive symptoms were associated with decreased GMV in the right superior medial gyrus across patient groups. Dyspareunia correlated negatively with cortical thickness in the left inferior temporal gyrus and left middle temporal gyrus.

Limitations, reasons for caution: The study groups differed in a few baseline-characteristics, including educational levels, smoking and BMI. While measuring pain perception thresholds, we did not attempt to mimic CPP by placement of the thermode on the abdominal wall.

Wider implications of the findings: Changes in gray matter volume associated with endometriosis differ from those observed in women with endometriosis-independent CPP. Our results underline an involvement of the cerebellum in pain perception and the pathogenesis of pain associated with endometriosis.

Study funding/competing interest(s): This work was funded by the START Program of the Faculty of Medicine, RWTH Aachen, Germany, and supported by the International Research Training Group (IRTG 2150) of the German Research Foundation (DFG)-269953372/GRK2150, Germany. S.T. was supported by postdoctoral fellowship of the Faculty of Medicine, RWTH Aachen, Germany. There are no conflicts of interest.

Trial registration number: DRKS00021236.