The role of neuropsychological changes in the manifestation and treatment of chronic pain

: (Alternative Format Thesis)

Abstract

Chronic pain is a disease of the central nervous system. Neuropsychological symptoms present in some conditions suggest changes in brain function similar to those typically seen in people with brain lesions. One striking example is Complex Regional Pain Syndrome (CRPS), which presents as sensory, motor, and autonomic dysfunctions in the affected body part. People with CRPS can also show distortions in body representation, spatial cognition, and other cognitive functions. These neuropsychological symptoms appear to contribute to the clinical manifestations of CRPS. The role of spatial attention biases was initially suggested by the apparent efficacy of a neurocognitive treatment that targets changes in spatial cognition, called prism adaptation. However, its effects on clinical symptoms of CRPS were only tested in small, uncontrolled studies, and the direct evidence of spatial biases in CRPS is often inconsistent. Thus, our current understanding of the nature and clinical relevance of the neuropsychological symptoms is limited, as is the evidence of the effectiveness of neurocognitive treatments for CRPS. This thesis investigates (1) how neuropsychological functions are altered in CRPS, (2) whether neuropsychological symptoms contribute to the clinical manifestations of CPRS, and (3) whether prism adaptation treatment can reduce pain and other symptoms of CRPS. First, I present a critical literature review, concluding that people with CRPS can present with distorted representation of the affected limb, lateralised biases in spatial cognition, and non-spatially-lateralised cognitive deficits. I further discuss the potential mechanisms of such neuropsychological changes. The experimental studies I present in the following chapters primarily concern the spatial biases. They call into question some of the previous findings about neuropsychological changes in CRPS and their clinical relevance by showing that (a) when a significant spatial bias is observed at individual level, it is not necessarily stable over time, even when pain and body representation are, and (b) when I conducted robust assessments on a large sample, there was no evidence of spatial biases at group level, or of their relationship with clinical symptoms. Finally, I present a randomised controlled trial of prism adaptation treatment for CRPS, which showed no therapeutic effects on pain or CRPS severity beyond those of a control treatment, while overall CRPS severity decreased over time. These results suggest that the previously reported apparent benefits of prism adaptation could be attributed to movement of the affected limb or placebo effect. Overall, this thesis highlights the heterogeneity of neuropsychological symptoms in CRPS, and that previously reported changes in spatial cognition and their clinical relevance might have been overstated. Instead, my findings support the conclusion that motor function and body representation might be associated with clinical manifestation of CRPS and its progression over time. The major contribution of this thesis is providing a detailed and systematic evaluation of neuropsychological changes - especially spatial biases - in CRPS, and a robust test of prism adaptation treatment. The conclusions offer a balanced perspective on the role of neuropsychological functions in the manifestation of CRPS and suggest directions for improved treatments.

Date of Award	24 Jun 2020
Original language	English
Awarding Institution	University of Bath
Supervisor	Janet Bultitude (Supervisor) & Michael Proulx (Supervisor)