P177 Investigating the neural differences in individuals with chronic widespread pain or fibromyalgia and the effect of sleep: a cross-sectional study using data from UK Biobank
Authors: Silva Naiduwa W. I. L , Soni Anushka , Wanigasekera Vishvarani , Zhang Suyi , Wall Amanda J. W , Tracey Irene 
Published: April 2022

Abstract

Background/Aims
Sleep problems are common in fibromyalgia (FM) and chronic widespread pain (CWP), and may result in similar structural brain changes as those seen in chronic pain. However, the exact neural mechanisms are not fully understood. Studies to date are relatively small and yield conflicting results. The aim of this study is to investigate structural differences in brain regions of interest (ROI) in participants with FM or CWP from UK Biobank, a large-scale biomedical database, compared with healthy controls. We also explore the potential interaction of sleep on the volume of these ROIs, with the hypothesis that low sleep duration with chronic pain amplifies the atrophy seen.

Methods
Using T1 structural brain imaging data from UK Biobank, we defined cases as those experiencing CWP for 3+ months at the imaging visit or with a diagnosis of FM. Age- and sex-matched controls did not report any pain or chronic pain diagnoses at the imaging visit. Low sleep duration was defined as less than 7 hours of sleep in a 24-hour period in line with the recommended sleep duration of 7-9 hours. 22 brain ROIs were selected based on the existing literature. Pre-processed image-derived phenotype data for grey matter volumes were compared in brain ROIs using 2-way independent ANOVAs in SPSS.

Results
429 cases and 429 controls were included: (n = 664/858 [77.4%] female; mean [SD] age 62.0 ± 7.4). The volume of the grey matter in the bilateral insular cortices and anterior parahippocampal gyri, and the volume of the right pallidum, were all significantly smaller in cases compared to controls, p &lt; 0.05. In addition to the significant difference between the controls and cases in the right anterior parahippocampal gyrus, the interaction effect of sleep duration on pain was also significant, p &lt; 0.05. Even though there were no significant differences between the controls and cases in the grey matter volumes of the left posterior division of the cingulate gyrus, bilateral superior frontal gyri, right middle frontal gyrus, left posterior division of the parahippocampal gyrus, right precuneus cortex and left inferior frontal gyrus, pars opercularis, and the volume of the right thalamus, there was a significant interaction effect of sleep duration and pain status on their volumes, p &lt; 0.05.

Conclusion
This large-scale study confirms differences in grey matter volumes in key brain ROIs in those with chronic pain, highlighting neural changes in individuals suffering from CWP or FM, and a novel interaction of sleep on these areas. Perhaps these changes are due to neurotoxic effects of low sleep duration. Alternatively, low sleep duration and chronic pain may be caused by these structural differences. Evidently, further research is still needed to identify the directionality of these changes and their functional implications through longitudinal functional brain imaging studies, to identify the underlying cause of these structural differences.

Disclosure
N.W.I.L. Silva: None. A. Soni: None. V. Wanigasekera: None. S. Zhang: None. A.J.W. Wall: None. I. Tracey: None.