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Neuromyelitis optica spectrum disorder (NMOSD) is a chronic disease of the central nervous system that primarily affects the optic nerves and spinal cord. Despite similarities with relapsing-remitting multiple sclerosis (MS), NMOSD was recently recognized as a separate disease entity with different pathophysiological mechanisms and prognosis, and its clinical and imaging features are still being described. This project aims to explore brain and cervical spinal cord pathology in NMOSD by employing myelin water imaging, a magnetic resonance imaging method that has seen several applications in MS research. mcDESPOT is a novel technique based on multicomponent relaxometry that yields several quantitative tissue parameters, including the myelin water fraction, an index of myelin content, and T1 and T2 relaxation times, as well as structural volumetric measures. In this work, a mcDESPOT brain protocol was first acquired across three time points in healthy older adults on a single 3 Tesla scanner. Data on the test-retest reliability of mcDESPOT-derived indices are reported. Brain and cord mcDESPOT datasets were used to characterise focal and diffuse pathology in NMOSD in contrast with healthy controls. Results revealed abnormal parameters in several white matter regions, raising questions about the nature of non-lesional damage in the brain. Investigation of the thalamus showed normal volume, preserved microstructural integrity, and a link with a measure of information processing speed. Finally, cross-sectional and longitudinal measures of myelin content and atrophy in the cervical cord showed differences between NMOSD, MS and control groups. This work brings further evidence to address outstanding questions in NMOSD research regarding the nature and extent of brain involvement, the correlates of cognitive impairment, and the existence of subclinical disease progression between clinical relapses, and supports the use of mcDESPOT as an informative technique in the study of this rare disease in particular, and neurological disorders involving white matter in general. |
