Central changes associated with chronic pelvic pain and endometriosis

Abstract

Background: Chronic pelvic pain (CPP) is a significant public health problem with 1 million affected women in the UK. Although many pathologies are associated with CPP, the pain experienced is often disproportionate to the extent of disease identified and frequently no pathology is found (chronic pelvic pain syndrome). The central nervous system (CNS) is central to the experience of pain and chronic pain conditions in general are associated with alterations in both the structure and function of the CNS. This review describes the available evidence for central changes in association with conditions presenting with CPP.

Methods: A detailed literature search was performed to identify relevant papers, however, this is not a systematic review.

Results: CPP is associated with central changes similar to those identified in other pain conditions. Specifically these include, alterations in the behavioural and central response to noxious stimulation, changes in brain structure (both increases and decreases in the volume of specific brain regions), altered activity of both the hypothalamic-pituitary-adrenal axis and the autonomic nervous system (ANS) and psychological distress.

Conclusions: The evidence reviewed in this paper demonstrates that CPP is associated with significant central changes when compared with healthy pain-free women. Moreover, the presence of these changes has the potential to both exacerbate symptoms and to predispose these women to the development of additional chronic conditions. These findings support the use of adjunctive medication targeting the CNS in these women.

Keywords: central nervous system; chronic pelvic pain; endometriosis; neuroimaging.

Figure 1

Reprinted from Neuron, Tracey and Mantyh (2007) with permission from Elsevier. Nociceptive input is processed and modulated by ascending and descending pathways in the central nervous system. Many factors influence how the brain processes pain so the pain experience varies both within and between individuals. However, fMRI studies have shown that certain regions are frequently active in response to acute pain. Alterations in activity in some of these regions have been demonstrated in women with CPP (fMRI, functional magnetic resonance imaging).

Figure 2

Adapted from As-Sanie et al. (2012) with permission. The figure has been reproduced with permission of the International Association for the Study of Pain^® (IASP). The figure may not be reproduced for any other purpose without permission. Regional grey matter changes in women with and without endometriosis and chronic pelvic pain compared with healthy pain-free controls. Red regions represent areas in which grey matter decreased, while yellow regions represent where grey matter increased.

Figure 3

There are many factors that contribute to pain in CPP (circles). These factors might play a role in CPP in women with endometriosis (rectangles). PAG, periaqueductal grey; TRPV1, transient receptor potential cation channel subfamily V member 1; ERC, entorhinal cortex; HPA, hypothalamic pituitary axis.