Neuroimaging in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic disabling autoimmune disorder of the central nervous system histopathologically characterized by inflammation, multifocal demyelination, axonal damage and neuronal loss. Focal intensive demyelination and white matter infiltration by lymphocytes and mononuclear cells are pathological hallmarks of the disease (Ferguson et al., 1997; Lucchinetti et al., 2000). Complementary to the clinical evaluation, conventional magnetic resonance imaging (cMRI) plays a prominent role for diagnosis and assessment of patients with multiple sclerosis. It provides reliable detection and quantitative estimation of focal white matter lesions in vivo. Modern criteria involve MRI parameters for the diagnosis of MS and for predicting conversion to clinically definite MS in patients who present with a first clinical episode (eg, unilateral optic neuritis) suggestive of disease onset. A diagnosis of multiple sclerosis is based on showing disease dissemination in space and time and excluding other neurological disorders that can clinically and radiologically mimic multiple sclerosis. However, neurological impairment of patients with MS is poorly associated with the lesion load observed on conventional MRI scans. The discrepancy between clinical and conventional MRI findings in MS is explained, at least partially, by the low sensitivity of conventional MRI in the detection of grey-matter involvement and diffuse damage in white matter. In order to overcome these limitations new uses of conventional MRI methods have evolved and nonconventional MRI techniques have been developed. These advances are expected to help in understanding the underlying disease processes and the accumulation of irreversible disability and therefore are promising tools in studies of disease evolution and clinical trials. Optical coherence tomography (OCT) -a new, sensitive and non-invasive transpupillary imaging methodis able to provide accurate and quantitative measurements of axonal loss in retina and therefore holds promise as a biomarker for neurodegeneration in MS. This chapter reviews the use of cMRI techniques to diagnosis and follow-up of patients with MS. It also summarizes the evolving non-conventional MRI and non-invasive optical techniques, which are sensitive to different aspects of MS pathology and are promising to further increase our understanding of disease pathophysiology and the mechanisms accounting for the accumulation of irreversible disability.