Background & Aims
Chronic abdominopelvic pain (CAPP) is common and primarily affects women(1). CAPP is highly heterogenous and can be caused by many pelvic pathologies, including endometriosis, irritable bowel syndrome (IBS), and bladder pain syndrome. It has long been known that chronic pain affects both grey (GM)(2) and white matter (WM)(3). However, while many reviews have summarized the GM and WM abnormalities in other chronic pain conditions, the literature regarding women with CAPP remains unexplored.
Our aim was to synthesize existing literature on structural and microstructural brain differences in women with CAPP. We aimed to identify differences between women with CAPP and pain-free controls. Additionally, we looked for evidence on the association between specific clinical variables (e.g. pain severity) and GM and WM abnormalities.
Methods
We conducted a systematic review, using the PRISMA 2020 guidelines (4). The review was registered with Prospero (https://www.crd.york.ac.uk/prospero/) in March 2022. The following databases were searched for published articles regarding brain structure in women with any CAPP condition: Embase (OvidSP)[1974-present], MEDLINE (OvidSP)[1946-present], PsycINFO (OvidSP)[1806-present], and Science Citation Index (Web of Science Core Collection) [1900-present] and an additional mop-up search performed in Google scholar. Resulting articles were screened by 4 independent authors blinded to each other’s ratings and the quality of included articles was evaluated using the Newcastle–Ottawa scale (5).
Results
The initial search identified 1087 articles. After screening, 30 English language articles were further analysed (21 structural GM, 9 diffusion WM). The most common CAPP conditions were IBS and dysmenorrhea.Comparing patients with controls, GM differences mainly occurred in the pain modulatory system, including lower GM volume in the insula and cingulate cortex in patients. Higher GM volume in patients was also seen, including in the hippocampus, parahippocampus, pre- and post-central gyrus. Findings from diffusion WM studies were inconsistent. However, identifiable abnormalities could be found in several relevant association, projection and commissural WM tracts that connect brain regions of the pain modulatory system. Clinical variables, including pain intensity and duration, were found to correlate with both GM and WM in women with CAPP. However, as these studies explored a wide range of clinical variables, there was significant heterogeneity regarding the method of evaluation.
Conclusions
Structural and microstructural brain abnormalities are found in women with CAPP and are characterized by both higher and lower regional GM volume and altered WM tracts. Many of these findings are within/between known pain modulatory areas. Whilst clinical variables appear to be important, heterogeneity between studies prevents a more detailed understanding of these relationships. Standardizing brain imaging analysis pipelines and tools for assessing clinical variables would enhance the ability to synthesise data in the future. It is notable that many of the conditions associated with CAPP in women were not well represented amongst these studies. For example, endometriosis was particularly underrepresented, with only one GM volumetric study and no diffusion WM studies published. Considering that 1 in 10 women of reproductive age are estimated to have this condition, further research is needed as findings may not necessarily be in line with those found in other chronic pain conditions.
References
(1) Zondervan KT, Yudkin PL, Vessey MP, Dawes MG, Barlow DH, Kennedy SH. Prevalence and incidence of chronic pelvic pain in primary care: evidence from a national general practice database. Br J Obstet Gynaecol. 1999 Nov;106(11):1149-55. doi: 10.1111/j.1471-0528.1999.tb08140.x. PMID: 10549959.
(2) Smallwood RF, Laird AR, Ramage AE, Parkinson AL, Lewis J, Clauw DJ, Williams DA, Schmidt-Wilcke T, Farrell MJ, Eickhoff SB, Robin DA. Structural brain anomalies and chronic pain: a quantitative meta-analysis of gray matter volume. J Pain. 2013 Jul;14(7):663-75. doi: 10.1016/j.jpain.2013.03.001. Epub 2013 May 17. PMID: 23685185; PMCID: PMC4827858
(3) Coppieters I, Meeus M, Kregel J, Caeyenberghs K, De Pauw R, Goubert D, Cagnie B. Relations Between Brain Alterations and Clinical Pain Measures in Chronic Musculoskeletal Pain: A Systematic Review. J Pain. 2016 Sep;17(9):949-62. doi: 10.1016/j.jpain.2016.04.005. Epub 2016 Jun 3. PMID: 27263992.
(4) Moher D, Liberati A, Tetzlaff J, Altman DG; PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Int J Surg. 2010;8(5):336-41. doi: 10.1016/j.ijsu.2010.02.007. Epub 2010 Feb 18. Erratum in: Int J Surg. 2010;8(8):658. PMID: 20171303.
(5) https://www.ohri.ca/programs/clinical_epidemiology/oxford.asp
Presenting Author
Miriam Szabo
Poster Authors
Miriam Szabo
MD
University of Oxford
Lead Author
Ana Kisovar (MD)
Nuffield Department of Women’s & Reproductive Health, University of Oxford
Lead Author
Nia Roberts
Bodleian Health Care Libraries, University of Oxford
Lead Author
Razneen Shah
University of Oxford
Lead Author
Emily Tan
Nuffield Department of Women’s & Reproductive Health, University of Oxford
Lead Author
Gwenaëlle Douaud (Phd
Assoc. Prof.)
Wellcome Centre for Integrated Neuroimaging, Nuffield Department of Clinical Neurosciences, Universi
Lead Author
Katy Vincent DPhil BSc MBBS MRCOG
University of Oxford
Lead Author
Topics
- Gender/Sex Differences