Changes in regional gray matter volume in women with chronic pelvic pain: a voxel-based morphometry study

Chronic pelvic pain (CPP) is a highly prevalent pain condition, estimated to affect 15%-20% of women in the United States. Endometriosis is often associated with CPP, however, other factors, such as preexisting or concomitant changes of the central pain system, might contribute to the development of chronic pain. We applied voxel-based morphometry to determine whether women with CPP with and without endometriosis display changes in brain morphology in regions known to be involved in pain processing. Four subgroups of women participated: 17 with endometriosis and CPP, 15 with endometriosis without CPP, 6 with CPP without endometriosis, and 23 healthy controls. All patients with endometriosis and/or CPP were surgically confirmed. Relative to controls, women with endometriosis-associated CPP displayed decreased gray matter volume in brain regions involved in pain perception, including the left thalamus, left cingulate gyrus, right putamen, and right insula. Women with CPP without endometriosis also showed decreases in gray matter volume in the left thalamus. Such decreases were not observed in patients with endometriosis who had no CPP. We conclude that CPP is associated with changes in regional gray matter volume within the central pain system. Although endometriosis may be an important risk factor for the development of CPP, acting as a cyclic source of peripheral nociceptive input, our data support the notion that changes in the central pain system also play an important role in the development of chronic pain, regardless of the presence of endometriosis.