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Type: Theses
Title: Cognitive functioning in chronic fatigue syndrome
Author: Cockshell, Susan Jayne
Issue Date: 2016
School/Discipline: School of Psychology
Abstract: Chronic fatigue syndrome (CFS) involves long-standing and disabling fatigue of unknown aetiology that has a profound effect on a persons’ ability to function in daily life. However, little is understood of the condition and many of the research findings are conflicting, making the treatment and identification of causes problematic. Aside from fatigue, problems with memory and concentration are reported to be amongst the most disabling symptoms; however cognitive testing has revealed ambiguous results, with numerous studies finding deficits and others not. Few studies have investigated how these problems impact on daily functioning. In the absence of a recognised cause for CFS, cognitive problems have been attributed to a range of factors – including psychiatric problems, reduced effort, fatigue and poor sleep - but the contribution of each of these variables to cognitive impairment is unknown. This thesis was designed to clarify the type and magnitude of cognitive problems in CFS by undertaking a meta-analysis to examine the literature on cognitive testing (Chapter 3), which has previously only been summarised in narrative reviews. This was used to select the cognitive tests for a subsequent empirical study that investigated cognitive functioning in CFS, and explored factors that may influence impaired cognitive performance, specifically test effort (Chapter 4); motor slowing, psychological problems, fatigue and poor sleep, and also investigated factors that may be impacted by cognitive dysfunction, including everyday functioning, employment and mental fatigue (Chapter 5). Self-reported memory and attention problems form part of the CFS diagnostic criteria, consequently their relationship with memory and attention test results were also studied (Chapter 6). The results of these investigations have been published in four journal articles (Cockshell & Mathias, 2010, 2012, 2013, 2014). The meta-analysis analysed data from fifty studies that had assessed cognitive performance in adults who had been diagnosed with CFS (using published criteria) and in healthy controls (Chapter 3; Cockshell & Mathias, 2010). Compared to their healthy peers, persons with CFS showed large deficits on tests of reaction time and moderate deficits on tests of attention, memory and motor functioning. Smaller deficits were found on tests of visuospatial ability, cognitive reasoning and flexibility, indicating subtle problems in these areas. Global functioning and verbal abilities were unaffected. These findings indicated that people with CFS have moderate to large impairments in simple and complex information processing speed, and on tasks that required the sustained use of working memory. Tests that assessed these impairments were then selected for use in an empirical study, as were tests on which the CFS group was not impaired, to enable the differentiation of specific impairments from global deficits due to fatigue and/or lack of effort. The empirical study assessed 54 people with CFS and 54 age-, gender- and education- matched healthy controls on tests of reaction time, attention, memory, motor functioning, verbal and visuospatial abilities. All participants were additionally assessed for factors that may be related to cognitive impairment, which included a test of effort, a psychiatric interview (to screen for drug and alcohol abuse, and diagnose depressive and anxiety disorders), and questionnaire measures of psychological status (levels of depression and anxiety), CFS symptom severity, fatigue (prior, during and after the testing session), sleep quality, everyday functioning and self-reported problems with attention and memory. The initial analysis focussed on test effort which was assessed using the Validity Indicator Profile (VIP), to determine the extent to which people with CFS were performing to the best of their ability to ensure that their cognitive test results could be validly interpreted (Chapter 4; Cockshell & Mathias, 2012). The VIP identifies effort (high or low) and intention to perform well (or not) by analysing the pattern of responses, providing potential causes of poor performance. Four people in each group demonstrated an intention to perform well, but with reduced effort, possibly due to fatigue. Fifty people in each group demonstrated good effort, and only the results of this group were further analysed. The cognitive performance of the CFS and controls was then examined, and those measures on which the CFS group performed poorly were correlated with psychological status, CFS symptomatology and everyday functioning (Chapter 5; Cockshell & Mathias, 2013). People with CFS were found to be impaired on tests of simple and choice reaction time. Further analyses revealed that slowed choice reaction time was primarily the consequence of slower simple reaction times, and that neither were the consequence of impaired motor speed. The deficits in reaction time were not related to psychiatric status or severity of CFS symptoms. Similarly, the cognitive deficits were not related to everyday functioning, indicating that level of impairment could not be used to directly predict functional ability. Lastly, self-reported attention and memory problems were compared to attention and memory test results, and the impact of the testing session on fatigue was examined (Chapter 6; Cockshell & Mathias, 2014). Subjective and objective measures of attention and memory were not related in people with CFS or healthy controls, suggesting they may be measuring different constructs. However, people with CFS reported greater fatigue following cognitive testing and took several days longer than their peers to return to pre-testing fatigue levels. Overall, the findings from this thesis suggest that people with CFS are impaired in a number of cognitive domains, including memory and attention; consistent with the problems they frequently report. Many deficits are only minor and very specific, such as sustained working memory. The greatest impairment for people with CFS, however, was information processing speed; which was not explained by poor test effort, psychological problems or the severity of CFS symptoms (fatigue or poor sleep). People with CFS report experiencing cognitive problems and, although they are not directly related to their performance on cognitive tests, this research suggests that cognitive exertion can cause disabling fatigue for many days afterwards.
Advisor: Mathias, Jane Leanne
Krieg, Mark
Dissertation Note: Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Psychology, 2016.
Keywords: chronic fatigue syndrome
cognitive performance
cognitive tests
meta-analysis
effort
depression
anxiety
symptoms
self-report
Research by Publication
Provenance: Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.
This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals
DOI: 10.4225/55/58dc8dc6dc266
Appears in Collections:Research Theses

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