Cortical representation in complex regional pain syndrome

Abstract

Complex regional pain syndrome (CRPS) is a debilitating and persistent disorder characterised by pain and multiple system dysfunction. The sensory and motor features in particular have led to research into reorganisation in cortical function often termed maladaptive neuroplasticity . The overarching aim of this thesis was to examine the evidence for maladaptive cortical function in CRPS.

This thesis comprises 7 chapters. Following the Introduction (Chapter 1), Chapter 2 documents a systematic review and meta-analysis of the neuroimaging evidence concerning the function of the primary somatosensory cortex (S1) in CRPS. Chapter 3 is a systematic review and meta-analysis of the neuroimaging literature investigating the function of the primary motor cortex in CRPS. Chapter 4 reports the results of a functional MRI investigation into S1 hand representation size in patients with upper-limb CRPS and in healthy controls. Chapter 5 reports on a Rasch analysis, evaluating the measurement properties of the Pain Self-Efficacy Questionnaire (PSEQ). Chapter 6 explores the association between somatosensory representation (i.e. the results of Chapter 4) and clinical information on hand function in CRPS patients.

Chapters 2 and 3 revealed surprisingly limited evidence underpinning the assumptions of cortical reorganisation in CRPS and highlighted important methodological considerations that informed Chapters 4 and 6. Chapter 5 validated the use of the PSEQ in the CRPS patients recruited for Chapters 4 and 6. Chapter 4 provided the first evidence of a larger somatosensory representation of the healthy hand in CRPS, rather than a smaller representation of the affected hand, and that the effect cannot be explained by pain intensity or symptom duration. The lack of relationship between hand function and cortical representation in CRPS, as demonstrated in Chapter 6, raises new and important questions about mechanisms of neuroplasticity in CRPS.

S1 shrinkage and its pathological contribution to CRPS has long been accepted; indeed the only debate around the issue concerns whether the shrinkage in somatosensory representation contributes to, or is simply a result of, CRPS. This thesis identified gaps in the evidence base, then undertook a controlled, rigorous fMRI study, the findings of which prompt a re-conceptualisation of cortical reorganisation in people with CRPS.