Understanding functional cognitive disorder phenotypes in the differential diagnosis of neurodegenerative disease

Increasing numbers of people seek medical help for worrying cognitive symptoms. However, many patients attending services designed to detect neurodegenerative disease (such as memory clinics) do not have evidence of neurodegenerative disease, nor do their symptoms progress as such. In some, alternative causes are identified, such as medication or systemic illness. Others have been described as ‘worried well’, as having symptoms driven by anxiety and depression, or else reassured that they have no disease. These patients, many of whom have functional cognitive disorders, have been poorly served by research and as a result there is little evidence to guide effective treatment. Functional cognitive disorders are an important group of overlapping conditions in which cognitive symptoms are experienced as the result of reversible and inconsistent disturbances of attention and abnormal metacognitive interpretation. They have been neglected in functional disorder research and in neurodegenerative disease research, where they are an important differential diagnosis. The aims of this PhD were to build a firm definition of functional cognitive disorders, and to justify and explain how this definition might relate to previous and current diagnostic terminologies; to examine prevalence; to understand clinical associations; and to develop clinical methods to support accurate clinical diagnosis. This thesis investigates the terminologies and theoretical models that have previously been used to describe and explain functional cognitive disorders; systematically reviews prevalence and clinical features; describes comparative studies of healthy adults and simulators, and systematically reviews diagnostic performance of traditional psychometric tests of inconsistency (validity tests) in order to develop understanding of functional cognitive disorder mechanism and potential diagnostic methods. Finally, the thesis includes a clinical study of adults with cognitive symptoms, describing novel diagnostic techniques with wide potential utility