Normal pressure hydrocephalus (NPH) is characterised by a build-up of cerebrospinal fluid (CSF) in the brain despite apparently normal CSF pressure at lumbar puncture. In addition to movement and urinary symptoms, patients commonly display cognitive decline and apathy. NPH is recognised as an important cause of cognitive decline as it is thought be reversible with surgical CSF diversion (e.g. shunt surgery). However, this remains controversial and the neuropsychology of NPH is relatively poorly understood. Further, despite being the most commonly reported neuropsychiatric symptom in NPH, the significance of the symptom of apathy has not yet been elucidated. This thesis aims to expand on the neuropsychological and neuropsychiatric research in NPH, with the main objectives being to investigate neuropsychological outcome, and the significance of the symptom of apathy in NPH.
In order to investigate neuropsychological outcome following shunt surgery in NPH, a systematic review and meta-analysis was conducted (Chapter 2). The findings from studies which used a battery of neuropsychological tests to assess cognitive outcome in NPH were combined. Meta-analyses were conducted on pre-operative and difference scores for the most commonly used neuropsychological tests. These were seven tests which spanned global cognitive function, learning and memory, executive function and psychomotor speed. Results for all tests were significant in the direction of improvement. However, the significance of the results for two measures of executive function were deemed not to be robust. This is discussed in line with previous research which suggests that executive function may be less likely to improve following shunt surgery than other neuropsychological domains.
Next, the thesis focuses on the symptom of apathy. Chapter 3 investigated whether apathy in NPH relates to cognitive outcome and to a measure of ventricular enlargement. A reduction in apathetic symptoms following treatment was associated with better performance in a measure of global cognitive function. Further, larger ventricles (which may indicate greater disease severity/ brain damage) was associated with more severe apathy. A structural MRI study was then conducted to expand on these findings and to define brain structural correlates of apathy in NPH (Chapter 4). Results from this study suggested a potential role of the caudate nuclei in apathetic symptoms in NPH.
Finally, consideration is given to the assessment of apathy in NPH. Since apathy is rarely investigated in patients with NPH it is unclear which assessment method is most appropriate for this patient group. Chapter 5 presents findings from a feasibility study of a novel reward learning task to determine whether it might be useful as an objective measure of motivation and apathy in NPH
