Neuroimaging of chronic pain

• Main Author: Khusnullina, Aygul A.
• Other Authors: Mullins, Paul
• Published: Bangor University 2016
• Subjects: 616
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.701827

Chronic pain is a debilitating symptom of a wide range of conditions. These conditions are both highly prevalent and create adverse consequences for individuals and society. Whilst understanding of chronic pain conditions has improved, in a number of cases the mechanisms of chronic pain are not fully understood and no cure is available. It is appreciated that chronic pain is not only unpleasant in itself, but can also lead to a reorganisation of the nervous system resulting in further suffering. These factors present a justification for further investigation into the mechanisms and effects of chronic pain to enable progress towards more effective treatments. Neuroimaging techniques have helped our understanding the mechanisms and effects of chronic pain. Techniques have been developed to examine the structure, chemistry and activity of the brain. This thesis describes investigations that used neuroimaging to examine the effects of chronic pain on the human brain. A distinction has been drawn between chronic widespread pain (CWP) and chronic localised pain (CLP). Historically, the latter was seen as a condition of the peripheral components of the pain system. More recently, however, an understanding has been gained that central mechanisms may also be a factor in these conditions. The purpose of my investigations was to examine differences and similarities in the effects of two CWP and CLP conditions on the human brain. Fibromyalgia (FM) and Knee Osteoarthritis (OA) were chosen as representatives of these classes of condition. The effects on neurochemistry, brain structure and coordinated brain activity in these conditions were compared using magnetic resonance spectroscopy (MRS), voxel-based morphometry (VBM) and resting state functional connectivity (rs-FC). Using MRS I observed a reduction in N-Acetylaspartic acid (NAA) in the thalamus of OA patients when compared to FM. Using VBM I observed that grey matter volume (GMV) was reduced in the left brainstem and posterior cingulate cortex in FM patients when compared to OA. GMV was reduced in the left precentral, middle frontal and supramarginal gyri in OA when compared to FM. Using rs-FC I observed an increase in functional connectivity in the default mode network of FM patients when compared to OA. I observed increased functional connectivity within the default mode network (DMN) in both pain conditions compared to healthy controls. I also observed increased functional connectivity between the precuneus and regions in both the DMN and executive attention networks. Consideration is given to these findings in the context of previous relevant research. The implications of the results are related the patients’ own experience of their condition and links to clinical measures are also discussed. The findings provide further evidence for the neural basis of elements of patients’ experience of their condition and further understanding of the differences between the wider presentations of these conditions. The findings are drawn together to demonstrate where the effects of CWP and CLP overlap and where their effects contrast. Consideration is given to the mechanisms at work in these conditions that suggest differing effects on the components of the pain system and also to demonstrate where prolonged abnormal peripheral input may be a factor driving adaptation in CLP.